Aurélie Pénaud
email: aurelie.penaud@univ-brest.fr.

Frédérique Eynaud

María-Fernanda Sánchez-Goñi

B Malaize

Jean-Louis Turon

L Rossignol

Contrasting sea-surface responses between the western Mediterranean Sea and eastern subtropical latitudes of the North Atlantic during abrupt climatic events of MIS 3

Keywords: Dinocysts, SST and SSS quantification, Dansgaard-Oeschger, Greenland and Heinrich stadials, Alboran Sea, Iberian margin

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Introduction

The climate of the last glacial was characterised by a distinctive oscillatory mode, the so-called Dansgaard-Oeschger (D-O) cycles, originally described and defined in Greenland ice cores [START_REF] Johnsen | Irregular glacial interstadial recorded in a new Greenland ice core[END_REF][START_REF] Dansgaard | Evidence for general instability of past climate from a 250-kyr ice-core record[END_REF][START_REF] Grootes | Comparison of oxygen isotope records from the GISP2 and GRIP Greenland ice cores[END_REF] and paced by an empirical 1470-year factor, the nature of which being presently not known [START_REF] Schulz | Amplitude variations of 1470year climate oscillations during the last 100,000 years linked to fluctuations of continental ice mass[END_REF][START_REF] Moreno | Links between marine and atmospheric processes oscillating on a millennial timescale. A multiproxy study of the last 50,000 yr from the Alboran Sea (Western Mediterranean Sea)[END_REF][START_REF] Voelker | Mediterranean outflow strengthening during northern hemisphere coolings: A salt source for the glacial Atlantic?[END_REF]. Greenland Interstadials (GI) and Greenland Stadials (GS) including Heinrich Stadials (HS, following [START_REF] Sánchez-Goñi | Millennial-scale climate variability and vegetation changes during the Last Glacial: Concepts and terminology[END_REF], have previously been observed in marine climate records worldwide (e.g. [START_REF] Voelker | Global distribution of centennial-scale records for Marine Isotope Stage (MIS) 3: A database[END_REF]Hemming, 2004;[START_REF] Clement | Mechanisms of abrupt climate change of the last glacial period[END_REF]. The impacts of HS, which primarily correspond to large ice-sheet collapses, are now fairly well characterised in the NE Atlantic and Mediterranean areas. Their occurrence is associated with enhanced aridity in the adjacent borderlands [START_REF] Combourieu-Nebout | Enhanced aridity and atmospheric high-pressure stability over the western Mediterranean during the North Atlantic cold events of the past 50 k.y[END_REF][START_REF] Sánchez-Goñi | Synchronicity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the Mediterranean region[END_REF], increases in northward Saharan dust transport [START_REF] Moreno | Saharan dust transport and high-latitude glacial climatic variability: The Alboran Sea record[END_REF][START_REF] Bout-Roumazeilles | Connection between South Mediterranean climate and North African atmospheric circulation during the last 50,000 yr BP North Atlantic cold events[END_REF] and sea-surface temperature coolings in the western Mediterranean Sea (e.g. [START_REF] Cacho | Dansgaard-Oeschger and Heinrich event imprints in Alboran Sea paleotemperatures[END_REF] and on the Portuguese margin (e.g. [START_REF] Cayre | Paleoceanographic reconstructions from planktonic foraminifera off the Iberian Margin: Temperature, salinity, and Heinrich events[END_REF]Pailler and Bard, 2002;[START_REF] De Abreu | Millennial-scale oceanic climate variability off the western Iberian margin during the last two glacial periods[END_REF]. However, the forcing mechanisms behind the initiation of HS and the inferred reorganisation of Meridional Overturning Circulation within the last glacial period are still a matter of debate [START_REF] Kageyama | Glacial climate sensitivity to different states of the Atlantic Meridional Overturning Circulation: results from the IPSL model[END_REF]. Furthermore, a full understanding of this rapid transmission of millennial-scale climatic variability from boreal to subtropical latitudes, involving both atmospheric and oceanic processes, remains elusive. It has been demonstrated that convection in the western Mediterranean, and thus export of Mediterranean Outflow Water (MOW), was strengthened during GS of the last 50 ka [START_REF] Cacho | and percentages of the Mediterranean forest[END_REF][START_REF] Cacho | and percentages of the Mediterranean forest[END_REF][START_REF] Sierro | Impact of iceberg melting on Mediterranean thermohaline circulation during Heinrich events[END_REF][START_REF] Voelker | Mediterranean outflow strengthening during northern hemisphere coolings: A salt source for the glacial Atlantic?[END_REF][START_REF] Toucanne | Contourites of the Gulf of Cadiz: A high-resolution record of the paleocirculation of the Mediterranean outflow water during the last 50,000 years[END_REF][START_REF] Frigola | Evidence of abrupt changes in Western Mediterranean Deep Water circulation during the last 50 kyr: A high-resolution marine record from the Balearic Sea[END_REF]. Consequently, it has been suggested that the Mediterranean could act as a major trigger for the Meridional Overturning Circulation to switch from stadial to interstadial mode through the influence of MOW, providing saline water to the North Atlantic at times when the Meridional Overturning Circulation was partially interrupted [START_REF] Johnson | Ice age initiation by an ocean-atmospheric circulation change in the Labrador Sea[END_REF][START_REF] Bigg | Millennial-scale variability in the oceans: an ocean modelling view[END_REF][START_REF] Rogerson | Promotion of meridional overturning by Mediterranean-derived salt during the last deglaciation[END_REF][START_REF] Voelker | Mediterranean outflow strengthening during northern hemisphere coolings: A salt source for the glacial Atlantic?[END_REF]. The production of MOW is mainly controlled by the salinity budget of the Mediterranean Sea which depends on the climate characteristics over the region and therefore on dominant modes of climatic variability, notably the North Atlantic Oscillation (NAO). At present, the NAO pattern, oscillating at decadal and centennial scales, has a strong influence on climate over a large part of Europe during winter, by affecting the storm tracks and the associated relative moisture over the Mediterranean and northern Europe (e.g. [START_REF] Hurrell | Decadal trends in the North Atlantic Oscillation: Regional temperatures and precipitation[END_REF][START_REF] Serreze | Icelandic low cyclone activity: Climatological features, linkages with the NAO, and relationships with recent changes in the Northern Hemisphere circulation[END_REF][START_REF] Osborn | Evaluation of the North Atlantic Oscillation as simulated by a coupled climate model[END_REF]. Over the eastern Atlantic subtropical sector, it has been argued that this oscillation also has an imprint at centennial or millennial timescales, and has been implicated in abrupt climatic events of the last glacial (Sánchez-Goñi et al., 2002;[START_REF] Moreno | Links between marine and atmospheric processes oscillating on a millennial timescale. A multiproxy study of the last 50,000 yr from the Alboran Sea (Western Mediterranean Sea)[END_REF][START_REF] Bout-Roumazeilles | Connection between South Mediterranean climate and North African atmospheric circulation during the last 50,000 yr BP North Atlantic cold events[END_REF][START_REF] Daniau | Dansgaard-Oeschger climatic variability revealed by fire emissions in south-western Iberia[END_REF]Naughton et al., 2009). Consequently, a change between two periods, each of them characterised by sustained frequencies of a particular atmospheric configuration over several centuries, may have caused significant variations of hydrological exchanges through time between the Atlantic and the Mediterranean Sea [START_REF] Moreno | Links between marine and atmospheric processes oscillating on a millennial timescale. A multiproxy study of the last 50,000 yr from the Alboran Sea (Western Mediterranean Sea)[END_REF].

Previous high resolution palynological analysis of dinoflagellate cysts (dinocysts) and pollen on core MD95-2042, collected off Portugal, indicate abrupt changes in sea surface and atmospheric conditions, respectively, in response to D-O cycles [START_REF] Eynaud | Kystes de Dinoflagellés et Evolution paléoclimatique et paléohydrologique de l'Atlantique Nord au cours du Dernier Cycle Climatique du Quaternaire[END_REF][START_REF] Sánchez-Goñi | European climatic response to millennial-scale changes in the atmosphere-ocean system during the Last Glacial Period[END_REF].

Additionally, a climatic contrast has been observed with respect to precipitation between the SW Iberian margin and the Alboran region, with dryer conditions in southeastern Iberia than in its southwestern part [START_REF] Sánchez-Goñi | Synchronicity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the Mediterranean region[END_REF]. However, these studies do not quantify either changes in SST and SSS, or discuss the possible impact of the observed precipitation gradient on the hydrological conditions of both sides of the Strait of Gibraltar between 25 and 50 ka BP. To fill this gap, we have analyzed dinocyst assemblages from core MD95-2043, located in the Alboran Sea, and applied transfer functions. Furthermore, we have tested, for subtropical latitudes, the robustness of quantitative paleotemperature and paleosalinity reconstructions inferred from dinocysts against other proxy reconstructions (i.e. dinocyst-versus foraminiferaversus alkenone-derived SST, and dinocyst-derived SSS versus SSS estimates calculated on the basis of the δ 18 O of Globigerina bulloides associated with foraminiferal SST).

Core locations and present-day environmental settings

Calypso cores MD95-2043 (36°8.6'N; 2°37.3'W; 1841 m water depth; 36 m long) and MD95-2042 (37°48'N; 10°10'W; 3146 m water depth; 39.56 m long) were retrieved from the central Alboran Sea and the SW Iberian margin, respectively (Fig. 1), and were both collected by the oceanographic R/V Marion Dufresne during the 1995 International Marine Global Change Studies I (IMAGES I) cruise [START_REF] Bassinot | IMAGES MD 101, a coring cruise of the R/V Marion Dufresne in the North Atlantic and Norwegian Sea[END_REF].

The Mediterranean Sea is located between the path of the mid-latitude westerlies which dominate northern and central Europe, and the Azores High. At present, this basin experiences a typical seasonal cycle marked by cool-wet winters, and warm-dry summers. The resulting Mediterranean water budget is marked by a strong freshwater deficit due to a net excess evaporation [START_REF] Béthoux | Budgets of the Mediterranean Sea. Their dependence on the local climate and on the characteristics of the Atlantic waters[END_REF][START_REF] Béthoux | Paléo-hydrologie de la Mer Mediterranee au cours des derniers 20 000 ans[END_REF]. During winter and spring, intense cold and dry continental air outbursts induce strong evaporation and cooling in the northern Mediterranean Sea, and thus an increased density of surface water masses. As a result, surface waters sink in several specific Mediterranean regions, flow westward, and finally form the Mediterranean Outflow Water (MOW). The outflow current is exported at depth towards the Atlantic Ocean, through the narrow Strait of Gibraltar (main sill depth of 280 m) and is split into two stability levels: an upper core centred between 500 m and 800 m, and a more saline and dense lower core found between 1000 and 1400 m [START_REF] Ambar | Physical, chemical and sedimentological aspects of the Mediterranean outflow off Iberia[END_REF]. The MOW can be traced in the North Atlantic as a salinity and temperature maximum at about 1 km depth (e.g. Hill and Mitchelson-Jacob, 1993;Iorga and Lorzier, 1999;[START_REF] O'neill-Baringer | A review of the physical oceanography of the Mediterranean outflow[END_REF], and mixes progressively with North Atlantic Intermediate Waters (NAIW; [START_REF] Mauritzen | Production of dense overflow waters feeding the North Atlantic across the Greenland-Scotland Ridge. Part 1: Evidence for a revised circulation scheme[END_REF]. In the opposite direction, a North-Atlantic low-salinity surface current penetrates the Alboran Sea and mixes with Levantine Intermediate Waters (which resurface in the westernmost part of the Alboran Sea), forming the so-called Modified Atlantic Waters (MAW). The strong flow of MAW along the coast of Spain initiates the formation of two anticyclonic gyres, the Western and Eastern Alboran Gyres (WAG and EAG; Fig. 1) whose position and intensity fluctuate at a seasonal scale. The degree of development of the EAG, under which core MD95-2043 is located (Fig. 1), controls the position and intensity of the permanent Almeria-Oran Front (AOF; Fig. 1) [START_REF] Tintoré | A study of an intense density front in the eastern Alboran Sea: The Almeria-Oran front[END_REF][START_REF] Rohling | Abrupt hydrographic change in the Alboran Sea (western Mediterranean) around 8000 yrs BP[END_REF][START_REF] Rohling | The Mediterranean Sea: Present and Past[END_REF][START_REF] Viúdez | Time and space variability in the eastern Alboran Sea from March to May 1990[END_REF]. Upwelling cells occur along the AOF, this front marking the deflection of MAW along the Algerian margin, forming the Algerian Current (AC; Fig. 1).

The main modern hydrological structures and currents of the western Iberian margin form part of the North Atlantic Eastern Boundary Current (Fig. 1; [START_REF] Peliz | Winter upper ocean circulation in the Western Iberian Basin-Fronts, eddies and poleward flows: An overview[END_REF][START_REF] Relvas | Western Iberia Upwelling Ecosystem: An oceanographic overview[END_REF]. They are driven by the North Atlantic subtropical gyre intensity in relation to the seasonal displacement of the Azores High (e.g. [START_REF] Fiúza | Hidrologia e dinâmica das águas costeiras de Portugal[END_REF][START_REF] Fiúza | Water masses and their circulation off western Iberia during May 1993[END_REF]. Core MD95-2042 is located in the seasonal coastal upwelling band of the Portugal-Canary eastern boundary upwelling system that is active mainly from April to October [START_REF] Aristegui | Chapter 23 : oceanography and fisheries of the Canary current/Iberian region of the eastern North Atlantic (18a,E)[END_REF][START_REF] Peliz | Winter upper ocean circulation in the Western Iberian Basin-Fronts, eddies and poleward flows: An overview[END_REF]. The upwelling predominantly receives North Atlantic Central Waters (NACW) and, in part, also MOW [START_REF] Sánchez | Spring-summer climatological circulation in the upper layer in the region of Cape St.Vincent, southwest Portugal[END_REF]. Occasionally, during winter months, a warm northward-flowing surface current known as the Iberian Poleward Current or Portugal Coastal Counter Current is formed by coastal convergence along the western Iberian margin. This phenomenon occurs when weak northerlies are interspersed with strong south-southwesterly winds (e.g. [START_REF] Fiúza | Water masses and their circulation off western Iberia during May 1993[END_REF][START_REF] Peliz | Winter upper ocean circulation in the Western Iberian Basin-Fronts, eddies and poleward flows: An overview[END_REF]. This current can be traced as far as the Bay of Biscay where it is known as the "Navidad Current". Winter warming in the southern Bay of Biscay during Navidad years has been correlated with low values of the NAO index and this current was found to extend from Portugal to Norway in exceptional Navidad years [START_REF] Garcia-Soto | Navidad development in the southern Bay of Biscay: Climate change and swoddy structure from remote sensing and in situ measurements[END_REF].

Modern sea-surface conditions of the SW Iberian margin and Alboran Sea are characterised respectively by mean annual salinities of 36.5 and 37.1 psu (world dataset atlas compiled by [START_REF] Schmidt | Error analysis of paleosalinity calculations[END_REF]Bigg andRohling, 2000, http://data.giss.nasa.gov/o18data: Craig and Gordon dataset for the Iberian margin and C. Pierre dataset for the Alboran Sea), February SSTs are around 15.2 and 14.7°C, respectively, and August SSTs are around 20 and 23.7°C (WOA 2001).

Methodology

Chronostratigraphy

Cores MD95-2043 (central Alboran Sea) and MD95-2042 (SW Iberian margin), characterised by high sedimentation rates, are composed mainly of calcareous hemipelagic clays and have yielded high resolution paleoceanographic records (e.g. [START_REF] Cacho | Dansgaard-Oeschger and Heinrich event imprints in Alboran Sea paleotemperatures[END_REF]Shackleton et al., 2000, respectively).

The age model of core MD95-2042 is derived from 16 AMS 14 C dates and, for the period beyond AMS 14 C range, by graphical tuning of the MD95-2042 planktonic δ 18 O record with Greenland ice core δ 18 O records. The GISP 2 chronology (Bard et al., 2004) was used between 26 and 47 ka, and the GRIPSS09sea chronology [START_REF] Shackleton | Absolute calibration of the Greenland time scale: implications for Antarctic time scales and for d14C[END_REF] was applied between 47 and 77 ka.

Further details of the age models are given in [START_REF] Daniau | Dansgaard-Oeschger climatic variability revealed by fire emissions in south-western Iberia[END_REF] and [START_REF] Sánchez-Goñi | Contrasting impacts of Dansgaard-Oeschger events over a western European latitudinal transect modulated by orbital parameters[END_REF].

The age model of core MD95-2043 is based on 21 AMS 14 C dates and graphical tuning of the MD95-2043 alkenone SST record to GISP2 δ 18 O [START_REF] Cacho | Dansgaard-Oeschger and Heinrich event imprints in Alboran Sea paleotemperatures[END_REF]. Due to the recent improvement of the chronology of the SW Iberian margin core, some discrepancies in the two age models appear in the dates of the climatic events at around 40 ka BP. In these cases, we have slightly modified the chronology of the Alboran Sea record for the time interval between 40 and 50 ka, according to [START_REF] Sánchez-Goñi | Contrasting intrainterstadial climatic evolution between high and middle North Atlantic latitudes: A close-up of Greenland Interstadials 8 and 12[END_REF], in order to align the latter sedimentary sequence with that of the SW Iberian margin.

Dinoflagellate analysis

Dinoflagellates are flagellate protists that occur in both marine and freshwater environments, and which thrive in the depth range of 18-100 m in oceanic domains [START_REF] Dodge | The distribution of planktonic dinoflagellates and their cysts in the eastern and north-eastern Atlantic Ocean[END_REF][START_REF] Raine | The summer distribution of net plankton dinoflagellates and their relation to water movements in the NE Atlantic Ocean, west of Ireland[END_REF] and 0-10 m at the coastline. Water turbulence is greater in the neritic zone and represents a limiting factor for light penetration and thus the maximum depth of dinoflagellate habitats. Dinoflagellates reproduce primarily through fission, but sexual reproduction also occurs resulting in a resting cyst which is preserved in sediments [START_REF] Dodge | The distribution of planktonic dinoflagellates and their cysts in the eastern and north-eastern Atlantic Ocean[END_REF]Head, 1996).

The distribution of dinoflagellate cysts (dinocysts) reflects physico-chemical parameters of the overlying water masses (temperature, salinity, sea-ice cover, seasonality and nutrient availability) (e.g. [START_REF] Turon | Le palynoplancton dans l'environnement actuel de l'Atlantique Nord-oriental. Evolution climatique et hydrologique depuis le dernier maximum glaciaire[END_REF][START_REF] Mudie | Circum-Arctic Quaternary and Neogene marine palynofloras: paleoecology and statistical analysis[END_REF][START_REF] Matthiessen | Distribution patterns of dinoflagellate cysts and other organic-walled microfossils in recent Norwegian-Greenland Sea sediments[END_REF][START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF][START_REF] Devillers | Distribution of dinoflagellate cysts in surface sediments of the northern North Atlantic in relation to nutrient content and productivity in surface waters[END_REF][START_REF] Zonneveld | Geographical distributions of organic-walled dinoflagellate cysts in surficial sediments of the Benguela upwelling region and their relationship to upper ocean conditions[END_REF][START_REF] Marret | Atlas of modern organic-walled dinoflagellate cyst distribution[END_REF][START_REF] De Vernal | Organic-walled dinoflagellates : tracers of sea-surface conditions[END_REF].

Dinocyst analysis is therefore an essential tool for reconstructing Quaternary paleoenvironments (e.g. [START_REF] Turon | Le palynoplancton dans l'environnement actuel de l'Atlantique Nord-oriental. Evolution climatique et hydrologique depuis le dernier maximum glaciaire[END_REF][START_REF] Turon | Les asssemblages de kystes de dinoflagellés en Méditerranée occidentale (Mer d'Alboran): mise en evidence de l'évolution des paléoenvironnement depuis le dernier maximum glaciaire[END_REF][START_REF] Eynaud | Dinoflagellate cyst evidence of "Heinrich-like events" off Portugal during the marine isotopic stage 5[END_REF][START_REF] Eynaud | Comparison of the Holocene and Eemian palaeoenvironments in the South-Icelandic basin: dinoflagellate cysts as proxies for the North Atlantic surface circulation[END_REF][START_REF] Eynaud | Position of the Polar Front along the western Iberian margin during key cold episodes of the last 45 ka[END_REF][START_REF] De Vernal | Organic-walled dinoflagellate cysts: palynological tracers of sea-surface conditions in middle to high latitude marine environments[END_REF][START_REF] De Vernal | Dinoflagellate cyst assemblages as tracers of sea-surface conditions in the Northern North Atlantic, Arctic and sub-Arctic seas: The new 'n = 677' data base and its application for quantitative palaeoceanographic reconstruction[END_REF][START_REF] De Vernal | Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere during the last glacial maximum (LGM) based on dinoflagellate cyst assemblages[END_REF][START_REF] Mudie | Dinoflagellate cysts, freshwater algae and fungal spores as salinity indicators in Late Quaternary cores from Marmara and Black seas[END_REF][START_REF] Mudie | Late glacial, Holocene and modern dinoflagellate cyst assemblages in the Aegean-Marmara-Black Sea corridor: statistical analysis and re-interpretation of the early Holocene Noah's Flood hypothesis[END_REF][START_REF] Grøsfjeld | Last Interglacial marine environments in the White Sea region, north-western Russia[END_REF][START_REF] Penaud | Interglacial variability (MIS 5 and MIS 7) and dinoflagellate cyst assemblages in the Bay of Biscay (North Atlantic)[END_REF][START_REF] Penaud | What forced the collapse of European ice sheets during the last two glacial periods (150 ka B.P. and 18 ka cal B.P.)? Palynological evidence[END_REF][START_REF] Penaud | Contrasting Heinrich Events 1, 2, and LGM conditions off Morocco: Paleoceanographical evidences of warmer LGM and colder HE 1[END_REF].

Dinocyst assemblages were characterised at the species level on the sediment fraction smaller than 150 µm on 61 palynological slides for core MD95-2043 (this study) and on 71 slides for core MD95-2042 [START_REF] Eynaud | Kystes de Dinoflagellés et Evolution paléoclimatique et paléohydrologique de l'Atlantique Nord au cours du Dernier Cycle Climatique du Quaternaire[END_REF][START_REF] Sánchez-Goñi | European climatic response to millennial-scale changes in the atmosphere-ocean system during the Last Glacial Period[END_REF]. The preparation technique followed the protocol described by [START_REF] De Vernal | Technique de préparation et d'analyse en micropaléontologie[END_REF] and [START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF], slightly modified at the EPOC laboratory (Castera and Turon, http://www.epoc.ubordeaux.fr/index.php?lang=fr&page=eq_paleo26). Each subsample of 8 cm 3 was weighed, dried overnight and then weighed again to obtain dry weight. Subsamples were then washed through a 150 µm sieve and the fraction smaller than 150 µm was used for palynological analysis. After chemical and physical treatments (cold HCl, cold HF and sieving through single-use 10 µm nylon mesh screens), the final residue was mounted between slide and coverslip with glycerine jelly coloured with fuschin. Identifications and counts were performed using a Leica DM 6000 microscope at 400 × magnification, and counts aimed to reach 300 specimens wherever possible for each sample (cf. Appendix A). Taxonomic identifications are consistent with those of [START_REF] Fensome | DINOFLAJ[END_REF] and [START_REF] Fensome | The Lentin and Williams index of fossil dinoflagellates, 2004 edition[END_REF]. Brigantedinium cysts are grouped together and include all spherical brown cysts, since it is rarely possible to identify them at the species level due to their crumbled aspect which masks the archeopyle.

Dinocyst assemblages were described by the percentages of each species calculated on the basis of the total dinocyst sum including the few unidentified taxa and excluding pre-Quaternary cysts.

Palynomorph concentrations were calculated using the marker grain method [START_REF] De Vernal | Technique de préparation et d'analyse en micropaléontologie[END_REF]. Aliquot volumes of Lycopodium spores were added to each sample before chemical treatments in order to obtain palynomorph concentrations.

Quantitative reconstructions of sea-surface parameters

Dinocyst SST and SSS reconstructions

We used a transfer function based on the Modern Analogue Technique (MAT) to reconstruct seasurface hydrological parameters from dinocysts. The MAT principally uses the statistical distance between fossil (paleoceanographic record) and current (modern database) assemblages. The calculation of past hydrological parameters relies on a weighted average of the SST values of the best modern analogues found (minimum and maximum number of analogues imposed in the transfer functions are 5; cf. Appendix B for the list of analogues found for each sample). The maximum weight is given for the closest analogue in terms of statistical distance. The reader is referred to [START_REF] Guiot | Transfer functions: methods for quantitative paleoceanography based on microfossils[END_REF] for a review of theory of transfer functions and to de [START_REF] De Vernal | Dinoflagellate cyst assemblages as tracers of sea-surface conditions in the Northern North Atlantic, Arctic and sub-Arctic seas: The new 'n = 677' data base and its application for quantitative palaeoceanographic reconstruction[END_REF][START_REF] De Vernal | Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere during the last glacial maximum (LGM) based on dinoflagellate cyst assemblages[END_REF] for a step by step description of the application of transfer functions to dinocysts, including discussion about the degree of accuracy of the method.

The dinocyst transfer function used in this work (cf. [START_REF] De Vernal | Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere during the last glacial maximum (LGM) based on dinoflagellate cyst assemblages[END_REF]; GEOTOP website: http://www.unites.uqam.ca/geotop/monographie_n940/eng/index.shtml) is derived from a modern database comprising 60 dinocyst species and 940 stations from the North Atlantic, Arctic and North Pacific oceans and their adjacent seas, including the Mediterranean Sea (84 stations including station "M1039", cf. Fig. 1; [START_REF] Mangin | Distribution actuelle des kystes de dinoflagellés en Méditerranée occidentale et application aux fonctions de transfert[END_REF], as well as epicontinental environments such as the Estuary and Gulf of St. Lawrence, the Bering Sea and the Hudson Bay. The transfer function (n=940) is run under the "3Pbase" software [START_REF] Guiot | PPPbase, a software for statistical analysis of paleoecological data[END_REF]. This software was originally developed for pollen-based quantitative climate reconstruction (http://www.imepcnrs.com/pages/3pbase.htm) and was subsequently applied to dinocyst assemblages (e.g. de [START_REF] De Vernal | Dinoflagellate cyst assemblages as tracers of sea-surface conditions in the Northern North Atlantic, Arctic and sub-Arctic seas: The new 'n = 677' data base and its application for quantitative palaeoceanographic reconstruction[END_REF][START_REF] De Vernal | Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere during the last glacial maximum (LGM) based on dinoflagellate cyst assemblages[END_REF]). An index "Dmin", provided by the software "3PBase", allows testing the reliability of the reconstructions (cf. [START_REF] De Vernal | Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere during the last glacial maximum (LGM) based on dinoflagellate cyst assemblages[END_REF]. This index describes, for each sample analyzed, the distance between the closest analogue found by the transfer function and the fossil assemblage. A threshold value is calculated from the calibration of the database for the identification of non-similar or very bad analogues. This threshold value provided by the software "3PBase" is 71.72 and, below this value, the similarity between the modern data and the fossil record is considered significant (cf. Appendix B for the Dmin values calculated for each sample). The authors caution that the full reference set has been used for the calculations of hydrological parameters without any regional selection of samples within the modern database. In this study, we present February and August mean sea-surface temperatures (SST, with prediction errors of ±1.2°C and ±1.8°C respectively), and February and August mean sea-surface salinities (SSS, with prediction errors of ±1.7 for both).

Foraminiferal SST and SSS reconstructions

In the same way, we used a transfer function based on the MAT to reconstruct foraminiferal SST from the foraminiferal assemblages of cores MD95-2042 [START_REF] Cayre | Paleoceanographic reconstructions from planktonic foraminifera off the Iberian Margin: Temperature, salinity, and Heinrich events[END_REF] and MD95-2043[START_REF] Pérez-Folgado | Western Mediterranean planktonic foraminifera events and millennial climatic variability during the last 70 kyr[END_REF]. Calculation of past hydrological parameters relies on a weighted average of the SST values of the best 5 modern analogues found systematically. This transfer function has been developed at EPOC laboratory ("Environnements et Paléoenvironnements OCéaniques", Bordeaux1 University, France). The MAT (e.g. [START_REF] Kucera | Planktonic foraminifera as tracers of past oceanic environments[END_REF] is run under the "R" software using a script first developed for dinocyst transfer functions (http://www.cerege.fr/IMG/pdf/ECCOR_StatRAvr08.pdf). The modern database relies on a modern database of 1007 modern assemblages and is derived from the ones developed separately for the North Atlantic and the Mediterranean seas during the MARGO project [START_REF] Kucera | Reconstruction of sea-surface temperatures from assemblages of planktonic foraminifera: Multi-technique approach based on geographically constrained calibration data sets and its application to glacial Atlantic and Pacific Oceans[END_REF][START_REF] Kucera | Reconstruction of sea-surface temperatures from assemblages of planktonic foraminifera: Multi-technique approach based on geographically constrained calibration data sets and its application to glacial Atlantic and Pacific Oceans[END_REF]. These databases were merged together to offer a larger set of analogues for subtropical reconstructions over the last glacial period notably [START_REF] Eynaud | Position of the Polar Front along the western Iberian margin during key cold episodes of the last 45 ka[END_REF]Matsuzaki et al., in press). Modern hydrological parameters were requested from the WOA 2008 database using the tool developed during the MARGO project (http://www.geo.unibremen.de/geomod/staff/csn/woasample.html). This method allows the reconstruction of annual and seasonal (winter, spring, summer and fall) SST. In this paper, we present winter and summer mean SST with a prediction error of ± 1.2°C and ± 1.3°C respectively, and annual SST with a prediction error of ± 1.1°C [START_REF] Eynaud | Position of the Polar Front along the western Iberian margin during key cold episodes of the last 45 ka[END_REF]Matsuzaki et al., in press).

SSS estimates have been derived using the approach summarised in [START_REF] Malaizé | Sea surface salinity reconstructions as seen with foraminifera shells: Methods and cases studies[END_REF] for calibration of the salinity-water isotope relationship. [START_REF] Craig | Stable isotopes in Oceanographic Studies and Paleotemperatures[END_REF] established the first salinity-water isotope relationship as follows:

δ 18 Osw = 0.66 Since this pioneer work, many measurements have been performed and many different relationships, with different slopes, have been derived for different oceans (Ostlund et al., 1987[START_REF] Schmidt | Error analysis of paleosalinity calculations[END_REF][START_REF] Legrande | Global gridded data set of the oxygen isotopic composition in seawater[END_REF]. Discrepancies in slope and in intercept values are due to local characteristics, on spatial and temporal scales. For the Atlantic Ocean, an important dataset, established from several decades of oceanographic measurements, allows revision of the [START_REF] Craig | Stable isotopes in Oceanographic Studies and Paleotemperatures[END_REF] calibration and the determination of a new relationship, with a mean slope component of 0.558.

In order to estimate past changes in oceanic δ 18 Osw, [START_REF] Epstein | Revised carbonate-water isotopic temperature scale[END_REF] established a paleotemperature equation which links temperature with the isotopic composition of calcite (δ 18 Oc) in calcareous shells (e.g. foraminifera) and the ambient waters (δ 18 Osw). [START_REF] Shackleton | Oxygen isotope and palaeomagnetic stratigraphy of equatorial Pacific core V28-238: oxygen isotope temperatures and ice volumes on a 10 5 and 10 6 year scale[END_REF] have adapted the equation of [START_REF] Epstein | Revised carbonate-water isotopic temperature scale[END_REF] as follows: T = 16.9 -4.38 (δ 18 Oc -δ 18 Osw) + 0.13 (δ 18 Oc -δ 18 Osw) 2

Stable isotope δ 18 Oc measurements in cores MD95-2042 [START_REF] Cayre | Paleoceanographic reconstructions from planktonic foraminifera off the Iberian Margin: Temperature, salinity, and Heinrich events[END_REF][START_REF] Shackleton | Phase relationships between millennial-scale events 64,000-24,000 years ago[END_REF] and MD95-2043 [START_REF] Cacho | Dansgaard-Oeschger and Heinrich event imprints in Alboran Sea paleotemperatures[END_REF] were carried out on G. bulloides monospecific samples. Following the pioneer study of [START_REF] Duplessy | Surface salinity reconstruction of the North Atlantic Ocean during the last glacial maximum[END_REF], we corrected the summer temperature by 1°C for G. bulloides species. By solving the [START_REF] Shackleton | Oxygen isotope and palaeomagnetic stratigraphy of equatorial Pacific core V28-238: oxygen isotope temperatures and ice volumes on a 10 5 and 10 6 year scale[END_REF] equation, we obtain δ 18 Osw variations, which integrate the signal of both local and global variations. To remove the global influence of continental ice volume, we used estimations of past global δ 18 Osw changes based on benthic isotopic records and coral terrace growth [START_REF] Waelbroeck | Sea-level and deep water temperature changes derived from benthic foraminifera isotopic records[END_REF], and used the modern δ 18 Osw values (1.2 ‰ for the Alboran Sea and 0.97 ‰ for the Iberian margin) extracted from the world dataset atlas compiled by [START_REF] Schmidt | Error analysis of paleosalinity calculations[END_REF] and [START_REF] Bigg | An oxygen isotope dataset for marine waters[END_REF] (C. Pierre dataset for the Alboran Sea, and Craig and Gordon dataset for the Iberian margin, from http://data.giss.nasa.gov/o18data). The residual δ 18 Osw "ice-corrected" signal is then converted into quantitative SSS values for both cores, using a mean slope of 0.558. SSS uncertainties of around 1 psu derive from the prediction error of the foraminiferal SST reconstructions (1.8°C uncertainty linked with August SST reconstructions corresponds to a 0.45 ‰ uncertainty on a δ scale), as well as on uncertainties in the global δ 18 Osw changes linked to sea level changes (0.15 ‰).

Dinocyst assemblages through time

Concerning the species of the genus Brigantedinium spp., round brown cysts formed by heterotrophic dinoflagellates, it is important to take into account the fact that high occurrences of Brigantedinium spp. can be linked to better preservation under hypoxic or anoxic bottom conditions [START_REF] Combourieu-Nebout | A high resolution record of the last deglaciation in the central Mediterranean Sea : palaeovegetation and palaeohydrological evolution[END_REF][START_REF] Zonneveld | Geographical distributions of organic-walled dinoflagellate cysts in surficial sediments of the Benguela upwelling region and their relationship to upper ocean conditions[END_REF][START_REF] Kodrans-Nsiah | A natural exposure experiment on short-term species-selective aerobic degradation of dinoflagellate cysts[END_REF].

We can not exclude that Brigantedinium spp. may have been subjected to dissolution since deep ventilation in the western Mediterranean Sea (and thus oxidation processes) during GS was stronger than during GI of the last glacial (cf. benthic δ 13 C in Fig. 4; [START_REF] Cacho | Glacial rapid variability in deep-water temperature and δ18O from the Western Mediterranean Sea[END_REF].

However, Brigantedinium spp. are present throughout the Alboran core without any clear trend between few percentages during GS and high percentages during GI. We can thus expect to reconstruct dinocyst assemblages without significant preservational problems.

When comparing both cores (Fig. 2), we note extremely high relative abundances of Brigantedinium spp. (30-89%) on the SW Iberian margin (Fig. 2b). This may reflect the high productivity induced by permanent or intensified upwelling cells along the Portuguese margin during the last glacial (e.g. [START_REF] Abrantes | 200 000 yr diatom records from Atlantic upwelling sites reveal maximum productivity during LGM and a shift in phytoplankton community structure at 185 000 yr[END_REF][START_REF] Lebreiro | Productivity and paleoceanographic implications on the Tore Seamount (Iberian Margin) during the last 225 kyr: Foraminiferal evidence[END_REF]; this zone today is characterised by a seasonal upwelling system [START_REF] Peliz | Winter upper ocean circulation in the Western Iberian Basin-Fronts, eddies and poleward flows: An overview[END_REF] and Brigantedinium spp. percentages only reach a maximum of 2-5% in the modern database. Percentages of these cysts fluctuate more in the Alboran Sea, with pronounced oscillations (average of 19% and peaks reaching 30 to 45%) (Fig. 2a).

Dinocysts occurring during Greenland Stadials

Dinocysts which feature prominently during GS include Bitectatodinium tepikiense, Spiniferites lazus, Spiniferites elongatus, Impagidinium aculeatum, and Operculodinium centrocarpum in the Alboran Sea (Fig. 2a), and B. tepikiense, S. elongatus, cysts of Pentapharsodinium dalei, Lingulodinium machaerophorum and Nematosphaeropsis labyrinthus on the SW Iberian margin (Fig. 2b). It is also interesting to note that maximal dinocyst concentrations occur during GS off Portugal (most notably during HS 4; Fig. 2b) contrarily to what we observe in the Alboran record (Fig. 2a).

In the Alboran Sea, B. tepikiense increases during HS events, especially HS 3 and HS 4 (Fig. 2a), whereas it occurs during each GS on the SW Iberian margin, where it consistently makes up almost 10% of the total dinocyst assemblage (Fig. 2b). Today, B. tepikiense is mainly distributed between 40°N and 60°N in temperate to sub-arctic environments of the North Atlantic, with the highest abundances found south of the Gulf of St. Lawrence in coastal environments of Nova Scotia and the Gulf of Maine [START_REF] Wall | The environment and climatic distribution of dinoflagellate cysts in modern marine sediments from regions in the north and south Atlantic oceans and adjacent seas[END_REF][START_REF] Mudie | Circum-Arctic Quaternary and Neogene marine palynofloras: paleoecology and statistical analysis[END_REF]. This species is characteristic of areas marked by strong seasonal contrasts, with freezing winter SSTs and up to 16°C summer SST [START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF][START_REF] De Vernal | Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere during the last glacial maximum (LGM) based on dinoflagellate cyst assemblages[END_REF], and enhanced surface water stratification [START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF][START_REF] Marret | Atlas of modern organic-walled dinoflagellate cyst distribution[END_REF]. Previous results from the North Atlantic [START_REF] Zaragosi | Initiation of European deglaciation as recorded in the north-western Bay of Biscay slope environments (Meriadzek Terrace and Trevelyan Escarpment): a multi-proxy approach[END_REF][START_REF] Penaud | What forced the collapse of European ice sheets during the last two glacial periods (150 ka B.P. and 18 ka cal B.P.)? Palynological evidence[END_REF], the SW Iberian margin [START_REF] Sánchez-Goñi | European climatic response to millennial-scale changes in the atmosphere-ocean system during the Last Glacial Period[END_REF][START_REF] Turon | Land-sea correlations for the last glaciation inferred from a pollen and dinocyst record from the Portuguese margin[END_REF], and the western Mediterranean Sea [START_REF] Turon | Les asssemblages de kystes de dinoflagellés en Méditerranée occidentale (Mer d'Alboran): mise en evidence de l'évolution des paléoenvironnement depuis le dernier maximum glaciaire[END_REF][START_REF] Combourieu-Nebout | Enhanced aridity and atmospheric high-pressure stability over the western Mediterranean during the North Atlantic cold events of the past 50 k.y[END_REF] have shown increased abundances of B. tepikiense during HS.

S. elongatus develops during each GS with low percentages reaching 2-5% in the Alboran Sea (Fig. 2a) and 1-2% on the western Iberian margin (Fig. 2b). Maximum present-day occurrences of this species are observed in the Baffin Bay and Barents Sea, and this taxon is generally related to cool to temperate conditions [START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF]. The significant occurrence of B. tepikiense and S. elongatus is attributed to strong seasonality characterised by winter sea-surface temperatures probably less than 5°C [START_REF] Marret | Distribution of dinoflagellate cyst assemblages in surface sediments from the northern and western shelf of Iceland[END_REF].

Cysts of P. dalei occur sporadically in the Alboran Sea core (Fig. 2a) but mark clearly the cold events in core MD95-2042, most notably HS 2 and HS 4 (Fig. 2b). Cysts of P. dalei are well represented in modern sediments from polar to subpolar environments that experience summer sea-surface temperatures higher than 4°C [START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF][START_REF] Matthiessen | Distribution patterns of dinoflagellate cysts and other organic-walled microfossils in recent Norwegian-Greenland Sea sediments[END_REF][START_REF] Marret | Distribution of dinoflagellate cyst assemblages in surface sediments from the northern and western shelf of Iceland[END_REF][START_REF] De Vernal | Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere during the last glacial maximum (LGM) based on dinoflagellate cyst assemblages[END_REF]. They are particularly prevalent as part of the spring bloom within North Atlantic fjord systems [START_REF] Dale | New observations on Peridinium faeroense Paulsen (1905), and classification of small orthoperidinoid dinoflagellates[END_REF]Harland et al., 2004a,b).

In the Alboran Sea, we show that S. lazus is associated with cold HS and especially HS 5 (Fig. 2a). Today, the distribution of S. lazus is restricted to coastal regions of western Europe, always with low abundances (less than 2% of the dinocyst assemblages) [START_REF] Reid | Gonyaulacacean dinoflagellate cysts from the British Isles[END_REF]. This species can be regarded as a neritic temperate species of regions characterised by oligotrophic to eutrophic surface water conditions [START_REF] Reid | Gonyaulacacean dinoflagellate cysts from the British Isles[END_REF][START_REF] Harland | Distribution maps of Recent dinoflagellate cysts in bottom sediments from the North Atlantic Ocean and adjacent seas[END_REF].

Finally, the most striking feature visible in the dinocyst distribution during the D-O cycles is the systematic occurrence of Impagidinium aculeatum during GS in the Alboran Sea, with low percentages reaching a maximum of 5% (Fig. 2a). On the western Iberian margin, this species peaks during GI, although a local maximum is also observed during HS 5 (Fig. 2b). At present, this taxon is associated with warm water dinocyst assemblages; high relative abundances are found in tropical/subtropical oligotrophic open oceanic sites [START_REF] Turon | Le palynoplancton dans l'environnement actuel de l'Atlantique Nord-oriental. Evolution climatique et hydrologique depuis le dernier maximum glaciaire[END_REF]. In SW Iberian and western Mediterranean paleoclimate records, this species is characteristic of the Holocene with percentages close to 20% [START_REF] Combourieu-Nebout | A high resolution record of the last deglaciation in the central Mediterranean Sea : palaeovegetation and palaeohydrological evolution[END_REF][START_REF] Turon | Land-sea correlations for the last glaciation inferred from a pollen and dinocyst record from the Portuguese margin[END_REF][START_REF] Rouis-Zargouni | Environmental and climatic changes in the central Mediterranean Sea (Siculo-Tunisian Strait) during the last 30 ka based on dinoflagellate cyst and planktonic foraminifera assemblages[END_REF]. However, percentages close to 5% were also previously observed during cold stadials (HS 1 and HS 2) in a core from the Sicilian-Tunisian Strait [START_REF] Rouis-Zargouni | Environmental and climatic changes in the central Mediterranean Sea (Siculo-Tunisian Strait) during the last 30 ka based on dinoflagellate cyst and planktonic foraminifera assemblages[END_REF].

Dinocysts occurring during Greenland Interstadials

Dinocysts which feature prominently during GI in the Alboran Sea include Spiniferites mirabilis, Impagidinium patulum, L. machaerophorum, N. labyrinthus as well as some heterotrophic species (Protoperidinioids, Selenopemphix nephroides and Selenopemphix quanta, but excluding Brigantedinium spp. whose ecology is rather complex) (Fig. 2a). On the SW Iberian margin they include Impagidinium species (I. aculeatum and I. patulum), S. mirabilis, O. centrocarpum and S. nephroides (Fig. 2b). Unlike the SW Iberian margin (Fig. 2b), maximal dinocyst concentrations occur during GI in the Alboran Sea (especially during GI 8 and GI 12; Fig. 2a).

In the Alboran Sea, GI are characterised by the species S. mirabilis (Fig. 2a) with percentages on average four times higher than on the SW Iberian margin (Fig. 2b). The highest relative abundances of S. mirabilis are recorded during GI 7 and GI 8. Today, S. mirabilis is mainly distributed between 35°N and 50°N in warm temperate to temperate environments of the North Atlantic with highest occurrences found off the coast of Portugal and in the Bay of Biscay [START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF]. This species extends as far south as 10°N and is generally absent from areas with summer SST below 12°C and salinity below 28.5, and thrives optimally when winter SSTs are between 10°C and 15°C and summer SSTs are above 15°C.

On the SW Iberian margin, GI are characterised by I. patulum (Fig. 2b) with abundances four times higher than in the Alboran Sea (Fig. 2a). Most Impagidinium species occur today with maximum frequencies in tropical to warm temperate waters between 20°N and 35°N and are representative of full-oceanic conditions [START_REF] Harland | Distribution maps of Recent dinoflagellate cysts in bottom sediments from the North Atlantic Ocean and adjacent seas[END_REF][START_REF] Turon | Le palynoplancton dans l'environnement actuel de l'Atlantique Nord-oriental. Evolution climatique et hydrologique depuis le dernier maximum glaciaire[END_REF][START_REF] Bouimetarhan | Dinoflagellate cyst distribution in marine surface sediments off West Africa (6-17°N) in relation to sea-surface conditions, freshwater input and seasonal coastal upwelling[END_REF].

Spiniferites delicatus is common on the SW Iberian margin and is mainly linked with interstadial conditions (Fig. 2b), while it is rare in the Alboran Sea (Fig. 2a). S. delicatus is a temperate species adapted to warm and neritic conditions [START_REF] Wall | The environment and climatic distribution of dinoflagellate cysts in modern marine sediments from regions in the north and south Atlantic oceans and adjacent seas[END_REF][START_REF] Harland | Distribution maps of Recent dinoflagellate cysts in bottom sediments from the North Atlantic Ocean and adjacent seas[END_REF][START_REF] Marret | Distribution of dinoflagellate cysts in recent marine sediments from the east Equatorial Atlantic (Gulf of Guinea)[END_REF].

S. quanta, S. nephroides and some Protoperidinioids show a distribution pattern closely linked to GI in the Alboran Sea (Fig. 2a). This association also holds for S. nephroides on the SW Iberian margin, but is less obvious for S. quanta and Protoperidinioids as they also increase during GS (Fig. 2b). These latter taxa, represented by low relative abundances in the modern database and a scattered distribution in the North Atlantic [START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF], are derived from heterotrophic dinoflagellates and are mainly related to high food resources. Their heterotrophic strategy of nutrition probably links them to the presence of higher concentrations of nutrients in surface waters. S. quanta has previously been linked to the dynamics of upwelling cells off NW Africa [START_REF] Dodge | The distribution of planktonic dinoflagellates and their cysts in the eastern and north-eastern Atlantic Ocean[END_REF][START_REF] Penaud | Contrasting Heinrich Events 1, 2, and LGM conditions off Morocco: Paleoceanographical evidences of warmer LGM and colder HE 1[END_REF].

Opposite dinocyst patterns between Iberian and Alboran environments over D-O cycles

Other dinocyst species not described above, L. machaerophorum, N. labyrinthus, and O. centrocarpum, are an important component of the dinocyst assemblages and show opposite patterns in both cores N. labyrinthus shows very high percentages in the Alboran Sea (average 24%), where it occurs generally within GI (Fig. 2a). Peaks of this species systematically exceed 40% and can reach 60 to 70% of the total dinocyst assemblage. On the SW Iberian margin, this taxon is less prevalent (average of 4.5%) with peaks generally reaching 10% during GS (except during HS) (Fig. 2b). At present, N. labyrinthus is a typical open-ocean species found predominantly between 45°N and 65°N in the North Atlantic Ocean [START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF][START_REF] Matthiessen | Distribution patterns of dinoflagellate cysts and other organic-walled microfossils in recent Norwegian-Greenland Sea sediments[END_REF][START_REF] Marret | Distribution of dinoflagellate cyst assemblages in surface sediments from the northern and western shelf of Iceland[END_REF][START_REF] De Vernal | Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere during the last glacial maximum (LGM) based on dinoflagellate cyst assemblages[END_REF]. Maximum abundances of this species are recorded off southern Greenland where cold waters from the East Greenland and Labrador currents mix with warm North Atlantic waters of the Irminger Current [START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF][START_REF] Marret | Distribution of dinoflagellate cyst assemblages in surface sediments from the northern and western shelf of Iceland[END_REF]. This species, in association with B. tepikiense, was previously related to polar water incursions during MIS 5 cold substages off Portugal [START_REF] Sánchez Goñi | High resolution palynological record off the Iberian margin: Direct land-sea correlation for the Last Interglacial complex[END_REF][START_REF] Eynaud | Dinoflagellate cyst evidence of "Heinrich-like events" off Portugal during the marine isotopic stage 5[END_REF], and during the Younger Dryas off Portugal [START_REF] Turon | Land-sea correlations for the last glaciation inferred from a pollen and dinocyst record from the Portuguese margin[END_REF], in the Mediterranean [START_REF] Turon | Les asssemblages de kystes de dinoflagellés en Méditerranée occidentale (Mer d'Alboran): mise en evidence de l'évolution des paléoenvironnement depuis le dernier maximum glaciaire[END_REF][START_REF] Rouis-Zargouni | Environmental and climatic changes in the central Mediterranean Sea (Siculo-Tunisian Strait) during the last 30 ka based on dinoflagellate cyst and planktonic foraminifera assemblages[END_REF] and off NW Morocco [START_REF] Marret | Paleohydrology and paleoclimatology off Northwest Africa during the last glacial-interglacial transition and the Holocene : Palynological evidences[END_REF][START_REF] Penaud | Contrasting Heinrich Events 1, 2, and LGM conditions off Morocco: Paleoceanographical evidences of warmer LGM and colder HE 1[END_REF]. N. labyrinthus has also been positively correlated with nutrient-rich and cool waters [START_REF] Turon | Les asssemblages de kystes de dinoflagellés en Méditerranée occidentale (Mer d'Alboran): mise en evidence de l'évolution des paléoenvironnement depuis le dernier maximum glaciaire[END_REF][START_REF] Devillers | Distribution of dinoflagellate cysts in surface sediments of the northern North Atlantic in relation to nutrient content and productivity in surface waters[END_REF].

L. machaerophorum occurs during GI in the Alboran Sea, particularly GI 8, 9 and 12 (Fig. 2a), while it occurs during GS on the SW Iberian margin (Fig. 2b). L. machaerophorum is today considered to be a temperate to tropical coastal euryhaline species [START_REF] Mertens | Process length variation in cysts of a dinoflagellate, Lingulodinium machaerophorum, in surface sediments: Investigating its potential as salinity proxy[END_REF]. It dominates associations from the northern African and southern European Atlantic shelves, and it is also found in abundance in North African coastal upwelling regions [START_REF] Targarona | Recent dinoflagellate cyst distribution in the North Canary Basin, NW Africa[END_REF][START_REF] Sprangers | Modern organic-walled dinoflagellate cyst distribution offshore NW Iberia; tracing the upwelling system[END_REF] and near the Congo outlet [START_REF] Marret | Distribution of dinoflagellate cysts in recent marine sediments from the east Equatorial Atlantic (Gulf of Guinea)[END_REF]. Extremely high concentrations of these cysts have been found in areas with typical seasonally stratified water columns such as fjords, bays, and estuaries (e.g. [START_REF] Reid | Dinoflagellate cyst distribution around the British Isles[END_REF][START_REF] Bradford | The distribution of Recent organic walled dinoflagellate cysts in the Persian Gulf, Gulf of Oman, and north-western Arabian Sea[END_REF][START_REF] Dale | Dinoflagellate cyst analysis of Upper Quaternary sediments in core GIK 15530-4 from the Skagerrak[END_REF][START_REF] Lewis | Cysts and sediments: Gonyaulax polyedra (Lingulodinium machaerophorum) in Loch Ceran[END_REF][START_REF] Morzadec-Kerfourn | Distribution des kystes de dinoflagellés dans les sédiments Pléistocènes de la marge Guinéenne de l'Afrique (Equamarge I, 1983) = Distribution of dinoflagellate cysts in Pleistocene sediments of the Guinean margin of Africa, Equamarge I[END_REF][START_REF] Dale | Dinoflagellate cysts as indicator of cultural eutrophication in the Oslofjord, Norway[END_REF]. This taxon has often been related to warm and stratified surface waters [START_REF] Marret | Atlas of modern organic-walled dinoflagellate cyst distribution[END_REF], and has also been used as a proxy for fluvial inputs towards the ocean [START_REF] Zaragosi | Initiation of European deglaciation as recorded in the north-western Bay of Biscay slope environments (Meriadzek Terrace and Trevelyan Escarpment): a multi-proxy approach[END_REF][START_REF] Holzwarth | NW African climate variations during the last 47,000 years: Evidence from organic-walled dinoflagellate cysts[END_REF].

O. centrocarpum occurs frequently in the Alboran Sea record with percentages reaching 20 to 40% during almost every GS (Fig. 2a). On the SW Iberian margin, this species shows relatively low percentages, with peaks generally less than 10% during GI and reaching a maximum of 20% during GI 3 (Fig. 2b). This species is considered to be a cosmopolitan, cool to temperate taxon [START_REF] Turon | Le palynoplancton dans l'environnement actuel de l'Atlantique Nord-oriental. Evolution climatique et hydrologique depuis le dernier maximum glaciaire[END_REF][START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF][START_REF] Marret | Atlas of modern organic-walled dinoflagellate cyst distribution[END_REF], and an abundance pattern following the route of the North Atlantic Drift (NAD) has been identified from its present geographical distribution in North Atlantic surface sediments [START_REF] Turon | Le palynoplancton dans l'environnement actuel de l'Atlantique Nord-oriental. Evolution climatique et hydrologique depuis le dernier maximum glaciaire[END_REF][START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF].

This observation was previously used to interpret the presence of an active NAD at times when this species was abundant in the Quaternary North Atlantic sediments [START_REF] Zaragosi | Initiation of European deglaciation as recorded in the north-western Bay of Biscay slope environments (Meriadzek Terrace and Trevelyan Escarpment): a multi-proxy approach[END_REF][START_REF] Eynaud | Comparison of the Holocene and Eemian palaeoenvironments in the South-Icelandic basin: dinoflagellate cysts as proxies for the North Atlantic surface circulation[END_REF][START_REF] Penaud | Interglacial variability (MIS 5 and MIS 7) and dinoflagellate cyst assemblages in the Bay of Biscay (North Atlantic)[END_REF][START_REF] Penaud | What forced the collapse of European ice sheets during the last two glacial periods (150 ka B.P. and 18 ka cal B.P.)? Palynological evidence[END_REF].

Temperature and salinity records: convergences and discrepancies

SST: dinocysts versus planktonic foraminifera

Quantitative reconstructions derived from the two transfer functions (dinocyst and foraminifera) are not directly comparable since the reconstructed parameters are not exactly the same. The dinocyst transfer function 3PBase-940 only provides February and August SST reconstructions while the foraminiferal transfer function R-1007 only provides annual and seasonal-mean (i.e. winter, spring, summer and fall) SST reconstructions. However, February and August foraminiferal SST can be estimated using the MAT transfer function derived from [START_REF] Pflaumann | SIMMAX: a modern analogue technique to deduce Atlantic sea surface temperatures from planktonic foraminifera in deep-sea sediments[END_REF] which relies on a modern database of 692 modern assemblages (only Atlantic stations), improved during the MARGO project [START_REF] Kucera | Reconstruction of sea-surface temperatures from assemblages of planktonic foraminifera: Multi-technique approach based on geographically constrained calibration data sets and its application to glacial Atlantic and Pacific Oceans[END_REF]. It is, however, more appropriate for us to discuss the foraminiferal data from the R-1007 transfer function (Atlantic and Mediterranean modern databases) for the Alboran Sea core which is located at the boundary of the two basins. The comparison of winter versus February SST values on the 664 common stations from the foraminiferal north Atlantic databases (n=1007 versus n=692) generates a mean difference of 0.26°C (with a maximum difference of 1.95°C). For the summer versus August SST values, the mean difference is 0.37°C (with a maximum difference of 1.1°C). These values are within the range of the error bars of the foraminiferal reconstructions and therefore encourage us to consider that monthly and seasonal foraminiferal SST values can be discussed interchangeably.

Concerning dinocysts, the n=940 database also includes Mediterranean stations. It is worth noting that, among the 84 Mediterranean analogues (including 17 stations in the Alboran Sea), the only Mediterranean analogue found by the transfer function is located in the Alboran Sea and named "M1039" (Fig. 1; Appendix B). This is mainly the case during GI conditions (GIs 3,5,7,8,9,11,12 and 13;cf. Appendix B), suggesting that GI conditions in the Alboran Sea between 25 and 50 ka were roughly equivalent to conditions prevailing at the "M1039" site today (Fig. 1).

When comparing SST reconstructions from both micropaleontological proxies on the two cores, one can note that February versus winter SST values obtained with dinocysts (3PBase-940) and foraminifera (R-1007), respectively, are closer than August versus summer ones (Fig. 3).

However, the general good consistency of February versus winter SST is not valid for the SW Iberian margin during HS 5 with about 8°C difference between both micropaleontological reconstructions (dinocyst SST estimates around 13°C and foraminiferal ones close to 5°C; Fig. 3). This offset is unrealistically large given the prediction error for each method (around 1.2°C). This minor SST drop expressed in dinocyst populations may be underestimated, as also revealed by the annual alkenone-derived SST values warmer than the February dinocyst-based SST ones (Fig. 3). One reason may come from the occurrence of the dinocyst species Impagidinium aculeatum during HS 5 (Fig. 2). Indeed, on the western Iberian margin, this species peaks during GI, although a local maximum is observed during HS 5 (percentages slightly higher than 5%).

However, this species is associated with warm water dinocyst assemblages and is found today in tropical/subtropical oligotrophic open oceanic sites [START_REF] Turon | Le palynoplancton dans l'environnement actuel de l'Atlantique Nord-oriental. Evolution climatique et hydrologique depuis le dernier maximum glaciaire[END_REF]. Although the occurrence of this taxon during a cold HS is not understood, it may switch the transfer function towards warmer SST values.

August versus summer SST reconstructions for both cores show similar overall trends but differ more in terms of amplitudes, with dinocyst SSTs being 5 to 10°C higher than foraminiferal SST estimates (Fig. 3). Two hypotheses can be put forward with respect to this observation. Either the August/summer (dinocyst or/and foraminiferal) quantifications are less reliable or the discrepancy reflects an ecological bias. Dinocysts are indeed produced by dinoflagellates that thrive in the photic zone while foraminifera can migrate deeply in the water column with living depths ranging from 0 to 1000 m. Dinoflagellates, being found in shallower water, would thus record warmer SST consistently with a higher stratification during the warmest month, i.e.

August. Various biases between different micropaleontological reconstructions can thus occur in relation to the ecological strategy (depth of habitat and growth seasons) of the different planktonic populations [START_REF] De Vernal | Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere during the last glacial maximum (LGM) based on dinoflagellate cyst assemblages[END_REF]. The following comparison with alkenones will help us to decipher whether the foraminiferal or dinocyst signal is too cold or warm, respectively.

Finally, concerning the Alboran Sea core, one can note that dinocysts and foraminiferal show closer August versus summer SST values between 31 and 38 ka and larger offsets between 38 and 50 ka. This point will be further discussed in section 6.2.3. of this manuscript.

SST: transfer functions versus alkenones

Alkenone-derived SST from cores MD95-2043 [START_REF] Cacho | Dansgaard-Oeschger and Heinrich event imprints in Alboran Sea paleotemperatures[END_REF] and MD95-2042 (Pailler and Bard, 2002) has previously been compared with ice-core records, demonstrating a close linking between SSTs in the western Mediterranean and temperature developments over the wider North Atlantic region, including Greenland. Here, it appears that our dinocyst-based SST reconstructions for both cores match peak to peak with the SSTs derived from alkenones, showing minimum values during GS (Fig. 3). Furthermore, the alkenone-based SST, which records an annual signal of temperature, fluctuates systematically in between the temperature range given by seasonal dinocyst SST reconstructions and is closer to February than August SST (Fig. 3). A co-variation between February dinocyst SST and alkenone-derived SST reconstructions was previously observed off NW Morocco during the last glacial over the last 30 ka [START_REF] Penaud | Contrasting Heinrich Events 1, 2, and LGM conditions off Morocco: Paleoceanographical evidences of warmer LGM and colder HE 1[END_REF]. This would confirm the hypothesis that switches in mean annual temperatures were dominated by, and thus weighted towards, the winter season during the last glacial cycle as suggested by [START_REF] Denton | The role of seasonality in abrupt climate change[END_REF].

The foraminiferal transfer function n=1007 also provides annual SST reconstructions that can directly be compared with the alkenone signal. One can note that annual SST values reconstructed with both proxies are closer during GI than during GS (Fig. 3). Foraminifera routinely provide much colder temperatures during GS, and especially during HS that are characterised by significant SST anomalies between 4 and 7°C (Fig. 3). This shift of annual SST values towards cold SSTs is mainly due to extremely cold summer SSTs reconstructed with foraminifera during GS (Fig. 3). This contrast has parallels to the previous observation on the considerable offsets between dinocyst and foraminiferal August versus summer SST. Since alkenones are synthesised by coccolithophorids which are single-celled algae, protists and phytoplankton such as dinoflagellates, we can assume that they both give a signature of seasurface hydrological changes occurring in the photic zone, while foraminifera may yield a bias towards colder SSTs, especially during GS. However, it will be crucial to understand if this finding reflects a real ecological strategy of foraminifera (different depths of habitat following different seasons) or a problem associated with the transfer function.

SSS: dinocyts versus planktonic foraminifera

Quantifications of salinity are of critical interest as they are fairly rare in paleoclimate studies. A major challenge in paleoceanography is to increase the availability of SSS reconstructions for comparison with climate models (e.g. MARGO project members, 2009). In our records, similar changes, both in amplitude and timing, are revealed through the comparison of February dinocyst-based SSS versus winter foraminiferal derived ones (Fig. 3). Numerical results are always very close or at least within the prediction error of 1-1.8 psu, except during HS 5 and GI 12 at the SW Iberian margin which are marked by differences of 2 to 3 psu between both micropaleontological proxies (Fig. 3). Comparison of the February/winter SSS data is particularly striking because the methods of quantification are different. One method requires MAT calculation of SST based on planktonic foraminifera and δ 18 O analysis (e.g. [START_REF] Malaizé | Sea surface salinity reconstructions as seen with foraminifera shells: Methods and cases studies[END_REF], while the other one is obtained on the basis of MAT transfer function applied to dinocyst assemblages (e.g. [START_REF] De Vernal | Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere during the last glacial maximum (LGM) based on dinoflagellate cyst assemblages[END_REF]. However, correlations between fluctuations in August dinocyst-based SSS and summer foraminiferal derived ones are less evident with fluctuations similar in timing but divergent in terms of amplitudes, especially for the Alboran Sea (Fig. 3).

For the SW Iberian margin, our study shows that major low salinity events are recorded during HS (Fig. 3b). HS 4 displays the maximum drop in February/winter SSS with values reaching 31 psu, corresponding to the largest fluxes of freshwater to the ocean over our study period. Our data for HS 3 (around 31.5-32.5 psu, 4 psu lower than the modern value) also show a major low salinity event and are consistent with previous results acquired further north along the Celtic margin over the last 35 ka BP where this interval was also characterised by a 4 psu depletion in SSS (Eynaud et al., submitted).

For the Alboran Sea, the difference in the resolution of analysis between dinocyst and foraminiferal/isotope reconstructions makes it difficult to compare some sections (Fig. 3a). This is mainly due to the fact that foraminiferal SSS is calculated from both foraminiferal SST and planktonic δ 18 O data and the resolution of the δ 18 O record is lower than the foraminiferal SST record. For the whole Alboran Sea record, February/winter SSS shows changes of similar order of magnitude between each GS, with the strongest signal of freshening recorded during HS 4 reaching 33 psu (4 psu lower than the modern value).

Paleohydrological changes affecting subtropical Atlantic latitudes through D-O cycles

The new contribution of dinocyst assemblages in the Alboran Sea

Warm intervals (GI) in the Alboran Sea

During GI, we observe an expansion of warm temperate to tropical species with a trend of decreasing abundance, and decreasing February and alkenone SST, from immediately prior to a Heinrich Stadial to the next HS (Fig. 4). This pattern is similar to that seen in the Greenland ice core isotope records showing progressively shorter GI and smaller increases in Greenland air temperatures between HS 5 and HS 4 and between HS 4 and HS 3 (Fig. 4, NGRIP GICC05).

This demonstrates a similar trend between Alboran SST and atmospheric temperatures over Greenland, involving a rapid transmission of Northern Atlantic climate changes into the western Mediterranean region.

When comparing the amplitude of warm taxa development during individual D-O warming (Fig. 4), we note less frequent occurrences of thermophilous taxa during the earlier interstadials (GI 12-9) than during the subsequent interstadials . This is consistent with pollen analysis conducted on the same core [START_REF] Fletcher | Orbital-and sub-orbital scale climate impacts on vegetation of the western Mediterranean basin over the last 48,000 yr[END_REF] demonstrating high values for Mediterranean forest during GI 8, 7, 6 and 5 reflecting the maximum in subtropical summer insolation associated with the precession minimum centred around 30-35 ka (Fig. 4). Such a development is also seen in paleo-vegetation records at nearby Alboran site ODP 976 [START_REF] Combourieu-Nebout | Enhanced aridity and atmospheric high-pressure stability over the western Mediterranean during the North Atlantic cold events of the past 50 k.y[END_REF] and on the SW Iberian margin (MD95-2042: Sánchez-Goñi et al., 2000).

The interstadials GI 8 and GI 12, immediately succeeding HS 4 and HS 5, respectively, exhibit particularly long and warm periods. They are both marked by high relative abundances of warm water dinocysts, high SST estimates (especially clear with alkenones; Fig. 4), and by the highest paleoproductivity conditions indicated by heterotrophic taxa in the early interstadials and high dinocyst concentrations in the second half of GI 8 and GI 12 (Fig. 4). In terms of sea-surface paleohydrology, GI 8 and GI 12 are thus very similar with a comparable bipartite structure (Fig. 4). Palynological investigations of GI 8 and GI 12 in the same Alboran Sea core showed that these periods were characterised by the strongest expansions of mixed oak forest between 48 and 15 ka [START_REF] Fletcher | Orbital-and sub-orbital scale climate impacts on vegetation of the western Mediterranean basin over the last 48,000 yr[END_REF]. Furthermore, [START_REF] Fletcher | Orbital-and sub-orbital scale climate impacts on vegetation of the western Mediterranean basin over the last 48,000 yr[END_REF] identified an Atlantic oceanic character during GI 12, in contrast to a markedly Mediterranean character during GI 8, linked to the precession minimum that likely enhanced the Mediterranean climate and caused an enhanced seasonal contrast between dry summers and wet winters [START_REF] Sánchez-Goñi | Contrasting impacts of Dansgaard-Oeschger events over a western European latitudinal transect modulated by orbital parameters[END_REF], 2009;[START_REF] Fletcher | Orbital-and sub-orbital scale climate impacts on vegetation of the western Mediterranean basin over the last 48,000 yr[END_REF]. Our dinocyst data also reveal a strong expansion of the species L. machaerophorum in the second half of GI 8, representing between 20 and 40% of the total dinocyst assemblage (Fig. 4). This species has sometimes been used to trace fluvial inputs [START_REF] Zaragosi | Initiation of European deglaciation as recorded in the north-western Bay of Biscay slope environments (Meriadzek Terrace and Trevelyan Escarpment): a multi-proxy approach[END_REF][START_REF] Holzwarth | NW African climate variations during the last 47,000 years: Evidence from organic-walled dinoflagellate cysts[END_REF] and could reflect higher river run-off to the Alboran Sea, providing further evidence for increased winter precipitations during this interval.

Throughout our record, heterotrophic dinocyst species (S. nephroides, S. quanta, and Protoperidinioids cysts) occur during each GI in the Alboran Sea (Fig. 4). Their occurrences suggest sea-surface conditions characterised by increased productivity [START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF], as also indicated by increased total dinocyst concentrations (Fig. 4). This general pattern of higher productivity during GI relative to GS has previously been discussed based on geochemical evidence (calcium carbonate, barium excess, and total organic carbon) from the same core [START_REF] Moreno | Millennial-scale variability in the productivity signal from the Alboran Sea record, Western Mediterranean Sea[END_REF]. Today, the two semi-permanent anticyclonic gyres found in the Alboran Sea represent energetic mesoscale features and the main forcing maintaining these gyres is the Atlantic jet which enters through the Strait of Gibraltar [START_REF] Bormans | A simple criterion for gyre formation by the surface outflow from a strait, with application to the Alboran Sea[END_REF][START_REF] Benzohra | Characteristics and circulation of the surface and intermediate water masses off Algeria[END_REF][START_REF] Garcia-Lafuente | Evolution of the Alboran Sea hydrographic structures during July 1993[END_REF][START_REF] Macias | Meteorologicallyinduced mesoscale variability of the North-western Alboran Sea (southern Spain) and related biological patterns[END_REF]. The intensity of the jet is typically modulated by atmospheric pressure variations over the western Mediterranean. Indeed, when atmospheric pressures are lower than average, configuration close to a NAO negative mode, westerlies prevail above the Mediterranean, the Atlantic jet flows northward near the Spanish coast and the western Alboran gyre is well developed in the entire western Alboran Sea.

The opposite (NAO positive mode) occurs when easterly winds prevail, the inflow of Atlantic waters is lower and the Atlantic jet is directed southward, reducing the western Alboran gyre extent [START_REF] Candela | Meteorologically forced subinertial flows through the Strait of Gibraltar[END_REF][START_REF] Garcia-Lafuente | Low frequency variability of the exchanged flows through the Strait of Gibraltar during CANIGO[END_REF][START_REF] Macias | Meteorologicallyinduced mesoscale variability of the North-western Alboran Sea (southern Spain) and related biological patterns[END_REF]. At an annual scale, on the basis of satellite imagery analysis (e.g. [START_REF] Garcia-Gorriz | The climatological annual cycle of satellite-derived phytoplankton pigments in the Alboran Sea[END_REF][START_REF] Baldacci | A study of the Alboran sea mesoscale system by means of empirical orthogonal function decomposition of satellite data[END_REF][START_REF] Macias | Phytoplankton distribution in the north-western Alboran Sea and meteorological forcing: a remote sensing study[END_REF][START_REF] Macias | Meteorologicallyinduced mesoscale variability of the North-western Alboran Sea (southern Spain) and related biological patterns[END_REF] maximum surface chlorophyll concentrations were usually found in winter and minimum values were observed in summer (July and August). Biological patterns are thus also tightly coupled to atmospheric pressure above the Mediterranean Basin with westerlies being shifted southward during winter. At the millennial-scale resolution of our study and in agreement with [START_REF] Moreno | Millennial-scale variability in the productivity signal from the Alboran Sea record, Western Mediterranean Sea[END_REF], our data suggest that GI conditions would exhibit a prolonged southward shift of the westerly wind belt, inducing a more intense Atlantic surface jet that favoured gyre-induced upwelling in the Alboran Sea.

Cold intervals (GS) recorded in the Alboran Sea

The association B. tepikiense -S. elongatus represents an indicator for the incursion of subpolar water masses at the Alboran site that is highly evident during HS (Fig. 4). This latter pattern is similar to that of the subpolar foraminifera Neogloboquadrina pachyderma s. recorded in the same core [START_REF] Cacho | Dansgaard-Oeschger and Heinrich event imprints in Alboran Sea paleotemperatures[END_REF]) that shows higher percentages during HS (Fig. 4). This foraminifer displays the highest percentages during HS 4, then HS 3 and finally HS 5, while B. tepikiense shows higher percentages during HS 3 compared to HS 4 (cf. Figs. 2 and4). B. tepikiense is absent from the Mediterranean Sea today, and highest abundances of this species occur in areas characterised by high-amplitude (10°C) seasonal temperature shifts [START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF]. Therefore, its occurrence during HS in Alboran Sea surface waters implies enhanced seasonal temperature contrast (15°C; cf. Fig. 5) compared to the present-day one (i.e. 10°C; 23.5°C in summer and 14.5°C in winter; cf. Fig. 5), caused by a strong decrease of winter SST (Fig. 4). Our February dinocyst SST reconstructions reinforce this hypothesis by showing low SST with values around 5.5°C and 6.5°C during HS 4 and HS 3, respectively, i.e. 9°C less than at present (Fig. 4). It is thus important to note that, in contrast to N. pachyderma s., B. tepikiense does not mark systematically colder intervals but intervals with larger seasonal contrasts. Our results are also in agreement with other observations made at ODP Site 976 (Alboran Sea) that reflect coeval increases of B. tepikiense with N. pachyderma s. percentages during HS, over the last 50 ka BP [START_REF] Turon | Les asssemblages de kystes de dinoflagellés en Méditerranée occidentale (Mer d'Alboran): mise en evidence de l'évolution des paléoenvironnement depuis le dernier maximum glaciaire[END_REF][START_REF] Combourieu-Nebout | Enhanced aridity and atmospheric high-pressure stability over the western Mediterranean during the North Atlantic cold events of the past 50 k.y[END_REF]. Our data thus confirm that sea-surface cooling in the Alboran Sea was mainly linked to the advection of cold Atlantic water to the western Mediterranean [START_REF] Cacho | Dansgaard-Oeschger and Heinrich event imprints in Alboran Sea paleotemperatures[END_REF]. Such cold-water advection occurred synchronously with regional cooling related to atmospheric conditions over the western Mediterranean [START_REF] Combourieu-Nebout | Enhanced aridity and atmospheric high-pressure stability over the western Mediterranean during the North Atlantic cold events of the past 50 k.y[END_REF][START_REF] Sánchez-Goñi | Synchronicity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the Mediterranean region[END_REF]. Indeed, on the adjacent continent, the Mediterranean forest (i.e. temperate taxa) collapsed (Fig. 4) and estimated winter atmospheric conditions indicate a 10°C lowering and a decrease of 400 mm in precipitation [START_REF] Sánchez-Goñi | Synchronicity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the Mediterranean region[END_REF].

The HS configuration contrasts with the other GS. In the Alboran Sea, before or during each GS (especially those not associated with HS conditions) we note pronounced peaks of O. centrocarpum (Fig. 4). The occurrence of O. centrocarpum in the Alboran Sea, whose presentday distribution directly mirrors the flow path of the NAD, may result from the influx of cool North Atlantic waters entering into the Mediterranean; temperatures of these waters, while presumably low, remained above those of the subpolar waters that entered the Mediterranean during HS. GS events of the last glacial have been demonstrated to coincide with intensification of the deep circulation in the Mediterranean [START_REF] Cacho | Evidence for enhanced Mediterranean thermohaline circulation during rapid climatic coolings[END_REF][START_REF] Cacho | Glacial rapid variability in deep-water temperature and δ18O from the Western Mediterranean Sea[END_REF][START_REF] Sierro | Impact of iceberg melting on Mediterranean thermohaline circulation during Heinrich events[END_REF][START_REF] Frigola | Evidence of abrupt changes in Western Mediterranean Deep Water circulation during the last 50 kyr: A high-resolution marine record from the Balearic Sea[END_REF]. Our data suggest that the intensification of deep ventilation in the Alboran Sea, reflected in benthic δ 13 C data (Fig. 4; [START_REF] Cacho | Glacial rapid variability in deep-water temperature and δ18O from the Western Mediterranean Sea[END_REF], was synchronous with the advection of North Atlantic waters to the Mediterranean, as reflected by highest relative abundances of coolwater dinocyst taxa (Fig. 4).

We demonstrate two different patterns during GS: those associated with HS are marked by increased abundances of cold water species associated with subpolar waters, and those not associated with HS are marked by an expansion of cool North Atlantic species. Interestingly, it has been demonstrated that the densest Western Mediterranean Deep Water was formed during GS not associated with HS [START_REF] Cacho | Glacial rapid variability in deep-water temperature and δ18O from the Western Mediterranean Sea[END_REF][START_REF] Frigola | Evidence of abrupt changes in Western Mediterranean Deep Water circulation during the last 50 kyr: A high-resolution marine record from the Balearic Sea[END_REF]. More precisely, it has been suggested that a strong mode of overturning prevailed during GS not associated with HS, an intermediate mode of overturning during HS and a weak mode of overturning during GI [START_REF] Sierro | Impact of iceberg melting on Mediterranean thermohaline circulation during Heinrich events[END_REF][START_REF] Frigola | Evidence of abrupt changes in Western Mediterranean Deep Water circulation during the last 50 kyr: A high-resolution marine record from the Balearic Sea[END_REF]. Strong overturning was expected during HS since strong and cold northern continental winds prevailed over the Mediterranean resulting in dry-cold conditions on land (Fig. 4; [START_REF] Combourieu-Nebout | Enhanced aridity and atmospheric high-pressure stability over the western Mediterranean during the North Atlantic cold events of the past 50 k.y[END_REF][START_REF] Sánchez-Goñi | Synchronicity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the Mediterranean region[END_REF]. However, the HS intermediate mode has been linked with a strong influence of subpolar waters that lowered seasurface salinity thus reducing deep water formation and favouring water column stratification [START_REF] Sierro | Impact of iceberg melting on Mediterranean thermohaline circulation during Heinrich events[END_REF]. The observation of subpolar species (N. pachyderma s. and B. tepikiense) during HS (especially HS 3 and HS 4), as well as the low winter and summer salinities reconstructed from dinocysts, lowered by around 0.5 to 1.5 psu compared to the other GS in both seasonal configurations (Fig. 3), within low precipitation phases, reinforce the idea of sustained cold conditions with subpolar water masses advection towards the Mediterranean Sea and decreased deep water formation.

Alboran Sea versus SW Iberian margin between 50 and 25 ka

SST reconstructions and paleoenvironmental signatures

In both cores, lowest SST estimates are observed during HS 4 which represents the most pronounced cold event between 25 and 50 ka, with February/winter SST of about 5.5°C and 4°C recorded in the Alboran Sea and the SW Iberian margin, respectively (Fig. 3). Previously, the coldest deep water temperatures in the Alboran Sea [START_REF] Cacho | Glacial rapid variability in deep-water temperature and δ18O from the Western Mediterranean Sea[END_REF], maximum concentrations of IRD off the Portuguese margin [START_REF] Thouveny | Rock magnetic detection of distal ice-rafted debris: Clue for the identification of Heinrich layers on the Portuguese margin[END_REF], and a significant increase in the transport of Saharan dust [START_REF] Moreno | Saharan dust transport and high-latitude glacial climatic variability: The Alboran Sea record[END_REF] were observed to occur during HS 4. This confirms the magnitude of HS 4 (cf. [START_REF] Eynaud | Position of the Polar Front along the western Iberian margin during key cold episodes of the last 45 ka[END_REF] in terms of expansion of polar waters towards the Iberian margin (i.e. February SST 11°C lower than modern ones) and even towards the western Mediterranean (i.e. February SST 9°C lower than modern ones), in phase with a nearly complete shutdown of the thermohaline circulation [START_REF] Maslin | Surface water temperature, salinity and density changes in the northeast Atlantic during the last 45,000 years: Heinrich events, deepwater formation and climate rebounds[END_REF][START_REF] Elliot | Changes in North Atlantic deep-water formation associated with the Dansgaard-Oeschger temperature oscillations (60-10 ka)[END_REF][START_REF] Roche | Constraints on the duration and freshwater release of Heinrich event 4 through isotope modelling[END_REF]. HS 3 is marked by a change in surface hydrological conditions with February/winter SST of about 6.5°C in the Alboran Sea and 5.5°C off Portugal (Fig. 3). Winter conditions seem thus to have been less severe during HS 3 than HS 4, although they are nevertheless characterised in both paleo-records by significant cooling.

Finally, HS 5 is the event which displays the weakest changes both in the Alboran Sea and off Portugal, where dinocyst February SST are about 9°C and 13°C, respectively (Fig. 4). However, foraminiferal winter SST estimates are close to 6°C and 5°C in the Alboran Sea and off Portugal, respectively. Quantifications derived from transfer functions appear less reliable during this interval. The alkenone annual signal (around 10.5-11°C in the Alboran Sea and 12-12.5°C off Portugal) probably provide an intermediate signature between dinocyst-based (too warm) and foraminiferal-based (too cold) February/winter SST estimates.

Micropaleontological evidence in the subpolar North Atlantic has shown that abrupt SST changes associated with the D-O events in Greenland were matched by SST variations of at least 3-5°C [START_REF] Bond | Evidence for massive discharges of icebergs into the North Atlantic ocean during the last glacial period[END_REF][START_REF] Bond | Correlations between climate records from North Atlantic sediments and Greenland ice[END_REF][START_REF] Elliot | Changes in North Atlantic deep-water formation associated with the Dansgaard-Oeschger temperature oscillations (60-10 ka)[END_REF]. In the subtropical North Atlantic, SST excursions of 4-5°C across stadial-interstadial transitions of the last glacial were recorded from the Bermuda Rise (alkenones: [START_REF] Sachs | Subtropical North Atlantic temperatures 60,000 to 30,000 years ago[END_REF]isotopes: Keigwin and Boyle, 1999) and off Portugal (alkenones: [START_REF] Bard | Hydrological impact of Heinrich events in the subtropical northeast Atlantic[END_REF][START_REF] Martrat | Four climate cycles of recurring deep and surface water destabilizations on the Iberian Margin[END_REF]. SST changes of up to 6°C are also documented in the western Mediterranean (alkenones: [START_REF] Martrat | Abrupt temperature changes in the western Mediterranean over the past 250,000 years[END_REF], due to southward shifts in the position of the Polar Front. Consistently with these previous results, we show here that the Alboran Sea and the SW Iberian margin experienced fluctuations of dinocyst SST of around 5-6°C between GI and GS, except for HS events and more specifically HS 4 with a SST drop of around 11°C off Portugal and of 8°C in the Alboran Sea. This demonstrates the extreme sensitivity of dinocysts to climate fluctuations in subtropical latitudes.

Multiproxy evidence for paleohydrological changes through time

During GI, the expansion of the Mediterranean forest (Fig. 4) was attributed to atmospheric conditions close to present-day ones with warm summer and wet winter conditions over southwestern Europe (e.g. [START_REF] Sánchez-Goñi | Synchronicity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the Mediterranean region[END_REF][START_REF] Combourieu-Nebout | Enhanced aridity and atmospheric high-pressure stability over the western Mediterranean during the North Atlantic cold events of the past 50 k.y[END_REF][START_REF] Bout-Roumazeilles | Connection between South Mediterranean climate and North African atmospheric circulation during the last 50,000 yr BP North Atlantic cold events[END_REF][START_REF] Daniau | Dansgaard-Oeschger climatic variability revealed by fire emissions in south-western Iberia[END_REF]. During those times, we show that warm temperate species S. mirabilis and I. patulum expanded in the Alboran Sea and on the SW Iberian margin, respectively (Fig. 4), and high SST is recorded at both sites during GI revealing seasurface conditions closer to present-day ones (Figs. 3 and4).

During GS, the decline of the Mediterranean forest (Fig. 4) and the development of steppe and semi-desert vegetation over the south-western European borderlands were attributed to intensified winter dryness with cold continental conditions affecting the western Mediterranean area (e.g. [START_REF] Sánchez-Goñi | Synchronicity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the Mediterranean region[END_REF][START_REF] Combourieu-Nebout | Enhanced aridity and atmospheric high-pressure stability over the western Mediterranean during the North Atlantic cold events of the past 50 k.y[END_REF][START_REF] Moreno | Saharan dust transport and high-latitude glacial climatic variability: The Alboran Sea record[END_REF][START_REF] Moreno | Links between marine and atmospheric processes oscillating on a millennial timescale. A multiproxy study of the last 50,000 yr from the Alboran Sea (Western Mediterranean Sea)[END_REF][START_REF] Roucoux | The response of NW Iberian vegetation to North Atlantic climate oscillations during the last 65,000 years[END_REF][START_REF] Bout-Roumazeilles | Connection between South Mediterranean climate and North African atmospheric circulation during the last 50,000 yr BP North Atlantic cold events[END_REF][START_REF] Daniau | Dansgaard-Oeschger climatic variability revealed by fire emissions in south-western Iberia[END_REF]. At that time, assemblages of cold-water dinocyst species, including B. tepikiense and S. elongatus developed, reflecting cold-water advection along the SW Iberian margin and towards the Alboran Sea (Fig. 4). However, unlike the western Iberian margin where B. tepikiense occurs during each GS, B. tepikiense expands principally in the Alboran Sea during HS, and especially during HS 3 and HS 4. In the western Mediterranean Sea, HS impacts were therefore greater than those associated with the other GS. [START_REF] Broecker | Abrupt climate change revisited[END_REF] has compiled data from several areas and has identified sites where the impact associated with North Atlantic Heinrich events is larger (eastern Brazil, central Florida, Arabian Sea, Chinese stalagmites, and western Mediterranean area), in contrast to sites where impacts are similar to those observed during the other stadials (Greenland ice and Cariaco Basin). To explain this discrepancy, [START_REF] Broecker | Abrupt climate change revisited[END_REF] involves the greater magnitude of northhemispheric sea ice expansion associated with North Atlantic Heinrich events which exceeded that associated with the other stadials.

B. tepikiense was previously used to trace subpolar water masses on the western Iberian margin [START_REF] Eynaud | Dinoflagellate cyst evidence of "Heinrich-like events" off Portugal during the marine isotopic stage 5[END_REF][START_REF] Turon | Land-sea correlations for the last glaciation inferred from a pollen and dinocyst record from the Portuguese margin[END_REF] and in the Alboran Sea [START_REF] Turon | Les asssemblages de kystes de dinoflagellés en Méditerranée occidentale (Mer d'Alboran): mise en evidence de l'évolution des paléoenvironnement depuis le dernier maximum glaciaire[END_REF][START_REF] Combourieu-Nebout | Enhanced aridity and atmospheric high-pressure stability over the western Mediterranean during the North Atlantic cold events of the past 50 k.y[END_REF] during HS. In our data, the observation of subpolar dinocysts in both cores, in phase and synchronous with peaks of N. pachyderma s. (Fig. 4), confirms the idea of the shift of the Polar Front (PF) towards southern latitudes during North Atlantic Heinrich events. Indeed, [START_REF] Eynaud | Position of the Polar Front along the western Iberian margin during key cold episodes of the last 45 ka[END_REF] proposed a conceptual scheme for the position of the PF on the western Iberian margin during Heinrich events and its influence on the local hydrology, and noticed that the protrusion of subpolar waters extended until approximately 40°N. Core MD95-2042 (37°48'N), at the southern limb of the Ruddiman belt (i.e. between 40 and 55°N;[START_REF] Ruddiman | Late quaternary deposition of ice-rafted sand in the subpolar north Atlantic (lat 40° to 65° N)[END_REF], was affected by subpolar waters and iceberg discharges. However, it is surprising to observe that the peaks of B. tepikiense are even larger during GS not associated with HS on the SW Iberian margin. When considering dinocyst, foraminiferal, and especially alkenone-based SST reconstructions, HS are characterised by the coldest temperatures (Figs. 3 and4). We can therefore assume that temperatures were probably too cold during summer months to permit the expansion of B. tepikiense. This hypothesis is reinforced by the large excursions towards cold summer temperatures observed with dinocyst and foraminiferal SST reconstructions (Fig. 3). The huge advection of subpolar waters down to the SW Iberian margin during each GS, and especially HS, is furthermore reinforced by the dinocyst SSS reconstructions that show a generally more pronounced influence of meltwater in this sector compared with the westernmost part of the Mediterranean Sea (average salinity offset of around 1 psu between the sectors; Fig. 3). This is especially true for HS 4, characterised by salinities of around 31 on the SW Iberian margin and 33 in the Alboran Sea (Fig. 3). We thus show the pronounced impact of subpolar waters affecting the SW Iberian margin during each GS and especially during HS, while the Alboran Sea is only impacted by huge freshwater discharges during HS.

A first attempt to interpret the dinocyst seasonality signal

Sea surface temperatures and precipitation are environmental parameters directly linked to seasonality in the study region, and the difference between August and February SST estimates derived from dinocysts may contain important information regarding the seasonality (Fig. 5).

Overall, the two cores show excursions in seasonality reconstructions towards a higher seasonal contrast during GS due to extremely cold February SST recorded during these cold intervals. At the SW Iberian margin, seasonal contrasts during GI appear similar to the present-day range, while extremely pronounced seasonal contrasts of roughly similar magnitude are recorded during each GS. The pattern of seasonality is very close to the relative abundance curve of B. tepikiense (Fig. 5). In the Alboran Sea, higher seasonal contrasts are mainly noted during HS and also correspond to higher percentages of B. tepikiense. It is not surprising to find parallels between this species and the seasonal signal since highest abundances of this species are found in areas today characterised by high-amplitude (10°C) seasonal temperature shifts [START_REF] Rochon | Distribution of Recent Dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent seas in relation to sea-surface parameters[END_REF].

In the Alboran Sea, it confirms the establishment of an enhanced seasonal temperature contrast compared to the present-day caused by a strong decrease in winter SST during HS [START_REF] Combourieu-Nebout | Enhanced aridity and atmospheric high-pressure stability over the western Mediterranean during the North Atlantic cold events of the past 50 k.y[END_REF]. At the SW Iberian margin, it reveals very clearly the marked shift between seasonal temperatures during each GS.

In the Alboran Sea, another climatic trend is superimposed on the general observations made above with, in broad terms, stronger seasonal contrasts during the early part of the record between 50 and 38 ka, compared to the period 38-31 ka (Fig. 5). Since seasonality and precession are closely linked, we show the precession curve [START_REF] Berger | Insolation values for the climate of the last 10 million years[END_REF] alongside the reconstruction of seasonality (Fig. 5). It appears that lower seasonal contrasts are observed during the precession minimum and vice versa (Fig. 5). We would have expected higher seasonal contrasts during the precession minimum since this orbital parameter enhanced the Mediterranean climate with warmer summer and wetter winters [START_REF] Meijer | The effect of precession-induced changes in the Mediterranean freshwater budget on circulation at shallow and intermediate depth[END_REF]. When looking at February SST reconstructions in the Alboran Sea, one can note that fluctuations during GS and GI are of similar magnitude (Fig. 5). The contrast is mainly due to August SST reconstructions that show colder values between HS 4 and HS 3 than between HS 5 and HS 4. Our data would suggest a link between the Alboran Sea paleohydrology and the precession signal through a climatic forcing acting on August temperatures. A first hypothesis could involve the general strengthening of the gyre-induced upwelling in the Alboran Sea during the time interval 38-31 ka favouring a cooling of sea-surface waters compared to the period 50-38 ka. However, the functioning of the gyres is mainly controlled today by winter conditions. Furthermore, no large differences are observed between 50-38 ka and 38-31 ka in terms of total dinocyst concentrations and heterotrophic dinocyst species, these latter proxies indicating paleoproductivity conditions probably connected to gyre-induced upwelling intensity. Greater stratification of the Alboran water column may also be suggested for the period 50-38 ka compared to the period 38-31 ka on the basis of the observation of dinocyst and foraminiferal August/summer SST (Fig. 3). Indeed, SSTs in August and summer are similar between 38 and 31 ka and are more distinct between 50 and 38 ka (Fig. 3). This might suggest a greater stratification of water masses during summers within the interval 50-38 ka and a stronger mixing of water masses during summers within the interval 38-31 ka. Warmer dinocyst SSTs might relate to sea-surface conditions while foraminiferal SSTs would incorporate SST signals at greater depths in the water column for the period 50-38 ka. Further investigation will be necessary to verify and explore on longer timescales: a) the imprint of precession on the seasonality changes inferred from dinocysts, and b) the functioning of the mesoscale energetic features in the Alboran Sea represented by two anticyclonic gyres today. 844

CONCLUSION

We have characterised glacial climate variability between 25 and 50 ka BP by comparing surface paleohydrology signals on both sides of the Strait of Gibraltar (Alboran Sea and SW Iberian margin). Comparison of dinocyst assemblages enables the reconstruction of hydrological features at both locations and we present, in this study, the first quantitative dinocyst reconstructions (SST and SSS) for MIS 3 obtained at mid-latitudes. Our hydrological quantifications acquired for both cores reproduce millennial-scale changes correlated to the D-O climatic variability, with a pattern of marked decrease in SST accompanied by a strong freshening of sea-surface waters evident during each GS on the SW Iberian margin and during HS in the Alboran Sea. Furthermore, we show similar patterns and amplitudes in SST reconstructions based on dinocysts, foraminifera and alkenones, and in SSS derived from dinocysts and foraminiferal SST coupled with planktonic δ 18 O. Larger discrepancies between dinocyst and foraminiferal estimates occur for summer reconstructions than for winter reconstructions, which are very similar in amplitude. We furthermore show the occurrence of cold taxa (including B. tepikiense and S. elongatus) during GS and the presence of thermophilous ones (S. mirabilis and Impagidinium spp.) during GI.

However, the amplitude of variation in these taxa is not equivalent at both sites. B. tepikiense characterises each GS in the SW Iberian margin while it only develops during HS in the Alboran Sea. This pattern reflects, in the Alboran Sea, the maximum climatic deterioration during HS and the incursion of low-salinity subpolar waters to the western Mediterranean. During other GS (i.e. excluding HS), conditions were less severe in the Alboran Sea as is reflected by the occurrence of O. centrocarpum at very high relative abundances in the Alboran Sea and low values on the SW Iberian margin. This species conceivably reflects the inflow of cool North Atlantic waters to the western Mediterranean, synchronously with stronger deep convection occurring at that time in the western Mediterranean. Finally, expansions of temperate to tropical taxa testify to the installation of warm sea-surface waters during GI. In the Alboran Sea, a high primary productivity pattern is deduced from heterotrophic species and high total dinocyst concentrations, suggesting gyreinduced upwelling due to prevailing southward-shifted westerlies above the Mediterranean at that time. The functioning of the gyre on multi-millennial timescales has also been discussed in light of seasonality reconstructions based on dinocysts. However, the relationships between gyre dynamics, seasonality and precession need to be explored in longer records covering several precession cycles. The dinocyst data thus exhibit regional trends and suggest distinct oscillations of sea-surface temperature and salinity, documenting the combined influence of atmospheric and hydrologic processes impacting on the western Mediterranean Sea and eastern subtropical latitudes of the North Atlantic during the abrupt climatic events of MIS 3.

Figure captions

Figure 1 :

 1 Figure 1: Area of interest with major sea-surface features. The studied cores MD95-2043

Figure 2 :

 2 Figure 2: MD95-2043 (a) and MD95-2042 (b). Core depths are displayed in centimetres along

Acknowledgements

Thanks to the French polar institute IPEV (Institut Paul Emile Victor), the captain and the crew of the Marion Dufresne and the scientific team of the 1995 IMAGES cruise. We wish to thank Mr. Y. Balut for his assistance at sea and M. Castera and O. Ther for invaluable technical assistance at the laboratory. We gratefully acknowledge the reviewers, whose comments have enabled us to greatly improve this manuscript. We thank W. Fletcher for improving the English language of the manuscript. This study was supported by the French CNRS and contributes to the EuroCLIMATE project RESOLuTION.

 Harland, R., Nordberg, K., Filipsson, H.L., 2004a