domain: sde sdu sdv phys

text:
R Delattre

Abraham

F Beny

V Bout-Roumazeilles

G R Davies

C Waelbroeck

A Bory

N Tribovillard

M Delattre

R Abraham

Radiogenic isotopic and clay mineralogical signatures of terrigenous particles as watermass tracers: new insights into South Atlantic deep circulation during the Last Termination

Keywords: Deglaciation, Paleoceanography, Southern Ocean, South Atlantic, Radiogenic isotopes, Clay mineralogy, Grain size distribution

Radiogenic isotopic and clay mineralogical signatures of terrigenous particles as water-mass tracers: New insights into South Atlantic deep circulation during the last termination

I. Introduction

The Southern Ocean (SO) is a key area for understanding the present and past carbon cycle. Direct observations indicate that the SO is a sink of atmospheric CO 2 today [START_REF] Quéré | Saturation of the Southern Ocean CO2 Sink Due to Recent Climate Change[END_REF][START_REF] Sallée | Surface to interior pathways of anthropogenic CO2 in the southern hemisphere oceans[END_REF] while it was likely a source of CO 2 to the atmosphere during the deglaciation [START_REF] Bouttes | Impact of oceanic processes on the carbon cycle during the last termination[END_REF][START_REF] Jaccard | Two Modes of Change in Southern Ocean Productivity Over the Past Million Years[END_REF]. Upwelling of CO 2 -rich deep water likely explains most of the CO 2 rise observed during Heinrich Stadials (HS; [START_REF] Ahn | Atmospheric CO2 and Climate on Millennial Time Scales During the Last Glacial Period[END_REF][START_REF] Anderson | Wind-Driven Upwelling in the Southern Ocean and the Deglacial Rise in Atmospheric CO2[END_REF][START_REF] Fischer | The role of Southern Ocean processes in orbital and millennial CO2 variations -A synthesis[END_REF][START_REF] Skinner | Ventilation of the Deep Southern Ocean and Deglacial CO2 Rise[END_REF][START_REF] Menviel | Atlantic-Pacific seesaw and its role in outgassing CO2 during Heinrich events[END_REF][START_REF] Menviel | Poorly ventilated deep ocean at the Last Glacial Maximum inferred from carbon isotopes: A data-model comparison study[END_REF]. Several other processes occurring in the Southern Ocean have also been invoked to explain the deglacial atmospheric CO 2 rise. For example, reduction of biological pump due to reduced iron fertilization [START_REF] Watson | Effect of iron supply on Southern Ocean CO2 uptake and implications for glacial atmospheric CO2[END_REF][START_REF] Wolff | Southern Ocean sea-ice[END_REF][START_REF] Fischer | The role of Southern Ocean processes in orbital and millennial CO2 variations -A synthesis[END_REF]Martinez-Garcia et al., 2014); reduced CO 2 solubility due to increased temperature of the ocean [START_REF] Köhler | Simulating low frequency changes in atmospheric CO2 during the last 740 000 years[END_REF][START_REF] Fischer | The role of Southern Ocean processes in orbital and millennial CO2 variations -A synthesis[END_REF]; reduction of sea ice extent [START_REF] Fischer | The role of Southern Ocean processes in orbital and millennial CO2 variations -A synthesis[END_REF]. As a consequence, the organization and extension of the Southern Ocean deep water-masses (i.e., Atlantic Meridional Overturning Circulation, AMOC; [START_REF] Skinner | Ventilation of the Deep Southern Ocean and Deglacial CO2 Rise[END_REF][START_REF] Shakun | Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation[END_REF][START_REF] Toggweiler | Midlatitude westerlies, atmospheric CO2, and climate change during the ice ages[END_REF] were studied, mainly using paleo-hydrological proxies (δ 18 O, δ 13 C, ε Nd of sea water, Δ 13 C; [START_REF] Barker | Interhemispheric Atlantic seesaw response during the last deglaciation[END_REF]Vasquez-Riveiros et al., 2010;[START_REF] Skinner | Ventilation of the Deep Southern Ocean and Deglacial CO2 Rise[END_REF][START_REF] Skinner | North Atlantic versus Southern Ocean contributions to a deglacial surge in deep ocean ventilation[END_REF][START_REF] Skinner | Radiocarbon evidence for alternating northern and southern sources of ventilation of the deep Atlantic carbon pool during the last deglaciation[END_REF][START_REF] Waelbroeck | The timing of deglacial circulation changes in the Atlantic[END_REF]Gottschalk et al., 2015b). By contrast, the terrigenous particle signal transported by these deep water-masses in the sub-Antarctic Atlantic Ocean remain poorly studied, even though locally it was successfully used to reconstruct the deep ocean circulation dynamical component (Diekmann et al., 2000 -Scotia Sea;Walter et al., 2000 -Scotia Sea and southwest South Atlantic;Kuhn and Diekmann, 2002 -Cape Basin). In this study, we aim to reconstruct the past evolution of deep-water masses (i.e. contribution to sedimentation, vertical and horizontal extensions, and speeds) during the last deglaciation using the signal carried in the terrigenous particles transported by these water masses. Sediment grain size distribution allows identifying the contribution of distinct oceanic currents [START_REF] Weltje | Genetically meaningful decomposition of grain-size distributions[END_REF][START_REF] Weltje | Quantitative models of sediment generation and provenance: State of the art and future developments[END_REF], and reconstructing the speeds of the main deep water-masses [START_REF] Mccave | Size sorting in marine muds: Processes, pitfalls, and prospects for paleoflow-speed proxies: SIZE SORTING IN MARINE MUDS[END_REF]McCave and Andrew, 2019). Grain-size distribution displays distinct modes [START_REF] Weltje | Quantitative models of sediment generation and provenance: State of the art and future developments[END_REF] that can be attributed to specific physical transport processes (e.g., wind, water currents, ice) and/or transport energy. Because grain-size distribution reflects both carrying vectors (e.g., wind, water currents, ice) and flow speed, several studies focused on the respective isotopic composition of distinct grain-size fractions in order to track distinct provenance patterns [START_REF] Meyer | Grain size control on Sr-Nd isotope provenance studies and impact on paleoclimate reconstructions: An example from deep-sea sediments offshore NW Africa[END_REF][START_REF] Bayon | Rare earth elements and neodymium isotopes in world river sediments revisited[END_REF][START_REF] Beny | Geochemical provenance of sediments from the northern East China Sea document a gradual migration of the Asian Monsoon belt over the past 400,000 years[END_REF]. Similarly, clay minerals are useful tracers of provenance, erosion balance, weathering, and transportation pattern of fine-grained sediments [START_REF] Moriarty | Clay minerals in Southeast Indian Ocean sediments, transport mechanisms and depositional environments[END_REF][START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF][START_REF] Kuhn | Late Quaternary variability of ocean circulation in the southeastern South Atlantic inferred from the terrigenous sediment record of a drift deposit in the southern Cape Basin (ODP Site 1089)[END_REF][START_REF] Montero-Serrano | Changes in precipitation regimes over North America during the Holocene as recorded by mineralogy and geochemistry of Gulf of Mexico sediments[END_REF]. Finally, radiogenic isotope compositions of sediments can be used to decipher the different provenances of terrigenous particles and determine their respective contributions through time [START_REF] Walter | Provenance and transport of terrigenous sediment in the south Atlantic Ocean and their relations to glacial and interglacial cycles: Nd and Sr isotopic evidence[END_REF][START_REF] Bayon | Hf and Nd isotopes in marine sediments: Constraints on global silicate weathering[END_REF].

This study focuses on the South Atlantic Ocean, where northern water-masses (North Atlantic Deep Water, NADW) and southern ones (Lower Circumpolar Deep Water, LCDW and Antarctic Bottom Water, AABW) mix, because this area is key for understanding the atmosphere-ocean exchanges that control CO 2 sequestration/outgassing. The reorganization of these deep water-masses during the deglaciation is still a subject of debate and their impact on deglaciation is not resolved [START_REF] Barker | Interhemispheric Atlantic seesaw response during the last deglaciation[END_REF][START_REF] Skinner | Ventilation of the Deep Southern Ocean and Deglacial CO2 Rise[END_REF][START_REF] Skinner | North Atlantic versus Southern Ocean contributions to a deglacial surge in deep ocean ventilation[END_REF][START_REF] Waelbroeck | The timing of deglacial circulation changes in the Atlantic[END_REF][START_REF] Adkins | The role of deep ocean circulation in setting glacial climates[END_REF][START_REF] Menviel | Atlantic-Pacific seesaw and its role in outgassing CO2 during Heinrich events[END_REF]Menviel et al., , 2015aMenviel et al., ,b, 2018)). Recent studies of the last deglaciation ventilation events in the South Atlantic Ocean demonstrated an apparent synergy between physical and biological processes [START_REF] Gottschalk | Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO2 changes[END_REF], whereas chemical and physical processes appear to be decoupled [START_REF] Roberts | Evolution of South Atlantic density and chemical stratification across the last deglaciation[END_REF]. These contrasting results

highlight the lack of constraints on the dynamical aspect of the water-masses mixing. In this paper, we combined grain-size distribution, clay mineralogy, and radiogenic isotope (Sr-Nd-Pb) analyses (on separated grain-size fractions) in order to investigate the evolution (horizontal and vertical extensions, pathways, speed) of deep-water-masses in the South Atlantic Ocean during the last termination.

II. General setting

Simplified geological map of the study area. Light blue text names riverine Figure 1: systems, dark blue text names seas, black text names oceanic basins, and white abbreviations names areas. In South America: Guyana Highlands -GH-, Brazilian Highlands -BH-, Argentinian Pampas -Pam-, Patagonia -Pat-; in Africa: Namibian deserts-Na-; in Antarctica: Ellsworth Mountains -EM-, Antarctic Peninsula -AntP-, Pensacola Mountains -PM-, Berkner Islands -BI-, Shackleton Range -SR-, Coats Land -CL-, Dronning Maud Land -DML-. Clay mineral inputs to the South Atlantic Ocean derived from the studies of [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF]; [START_REF] Diekmann | Terrigenous sediment supply in the Scotia Sea (Southern Ocean): response to Late Quaternary ice dynamics in Patagonia and on the Antarctic Peninsula[END_REF]; [START_REF] Walter | Provenance and transport of terrigenous sediment in the south Atlantic Ocean and their relations to glacial and interglacial cycles: Nd and Sr isotopic evidence[END_REF]; [START_REF] Guyot | Clay mineral composition of river sediments in the Amazon Basin[END_REF]; [START_REF] Bayon | Environmental Hf-Nd isotopic decoupling in World river clays[END_REF]; and [START_REF] Khondoker | New constraints on elemental and Pb and Nd isotope compositions of South American and Southern African aerosol sources to the South Atlantic Ocean[END_REF].

A. Deep water-masses

Modern South Atlantic deep circulation is characterized by the incursion of the NADW into the Southern Ocean, where it mixes/interacts with both the AABW and the Circumpolar Deep Water (CDW; figure 1). The southward NADW mainly flows as Deep

Western Boundary Current along the South American Margin before leaving the continental shelf and flowing eastward around 45°S [START_REF] Reid | On the total geostrophic circulation of the South Atlantic Ocean: Flow patterns, tracers, and transports[END_REF][START_REF] Larqué | On the intermediate and deep water flows in the South Atlantic Ocean[END_REF][START_REF] Stramma | On the water masses and mean circulation of the South Atlantic Ocean[END_REF]. A branch of the NADW crosses the Atlantic Ocean at the equator before to flow southward along the African margin and to reach the Indian Ocean via the Good Hope Cape [START_REF] Larqué | On the intermediate and deep water flows in the South Atlantic Ocean[END_REF]. In the Southern Ocean, NADW flows between two parts of the CDW: the Upper Circumpolar Deep Water (UCDW) flows above, whereas the Lower Circumpolar Deep Water flows underneath. The northern extension of the UCDW is very asymmetric with larger extent in the eastern part of the South Atlantic [START_REF] Larqué | On the intermediate and deep water flows in the South Atlantic Ocean[END_REF].

On the west side of the Mid-Atlantic Ridge (MAR), the LCDW penetrates into the Argentine Basin via the Drake Passage and flows northward into the Brazil Basin (Speer and Zend, 1993). On the east of the MAR, the LCDW is a major oceanic feature in the Cape Basin, where it becomes diluted in the Angola Basin [START_REF] Larqué | On the intermediate and deep water flows in the South Atlantic Ocean[END_REF]. The lower part of the LCDW is currently mixed with the upper part of the AABW [START_REF] Orsi | Circulation, mixing, and production of Antarctic Bottom Water[END_REF] that is produced heterogeneously along the Antarctic Shelf (Foster and Carmack, 1975;[START_REF] Orsi | Circulation, mixing, and production of Antarctic Bottom Water[END_REF]. Foster and Camarck (1975) demonstrated the formation of a very cold type of bottom water in the vicinity of the shelf break (the Polynyas mode) between 29 and 40°W and along the Antarctic Peninsula's tip, between 35 and 55°W and north of 65°S. Today this production occurs mainly in winter when seawater is close to freezing and becomes saltier due to sea ice formation (Foster and Camarck, 1975;[START_REF] Orsi | Circulation, mixing, and production of Antarctic Bottom Water[END_REF], which increases its density and promotes convection. This mode is called the Polynyas mode. However, in the Weddell Sea, a second mode of bottom water formation occurs: the Ice Shelf Water mode, which corresponds to bottom water formation under the Antarctic ice shelves due to super-cooling (Krueger et al. and references therein, 2012). The AABW is very thick in the Weddell-Enderby Basin (more than 4000 m; [START_REF] Orsi | Circulation, mixing, and production of Antarctic Bottom Water[END_REF] and is partially exported to the Argentine Basin via the eastern Scotia Sea (east and west of the South Sandwich Islands) toward the Brazil Basin via the Vema Channel, and to the Agulhas and Crozet basins [START_REF] Stramma | On the water masses and mean circulation of the South Atlantic Ocean[END_REF]. The AABW is a dominant oceanic feature south of 50°S although its' northern influence extents to around 10°S [START_REF] Reid | On the total geostrophic circulation of the South Atlantic Ocean: Flow patterns, tracers, and transports[END_REF].

The characteristics of deep water masses were not constant through time and the evolution of the AMOC is controversial [START_REF] Weber | Stability of the Atlantic Meridional Overturning Circulation in the Last Glacial Maximum climate[END_REF]Vasquez Riveiros et al., 2010;[START_REF] Waelbroeck | The timing of deglacial circulation changes in the Atlantic[END_REF][START_REF] Howe | North Atlantic Deep Water Production during the Last Glacial Maximum[END_REF]. Some studies have suggested that during the Last Glacial Maximum (LGM) the NADW was as strong as today but shallower [START_REF] Curry | Glacial water mass geometry and the distribution of δ13C of ΣCO2 in the western Atlantic Ocean[END_REF][START_REF] Gherardi | Glacial-interglacial circulation changes inferred from 231Pa/230Th sedimentary record in the North Atlantic region[END_REF]. Other studies suggest that it was weaker and shallower [START_REF] Menviel | Modeling atmospheric CO2, stable carbon isotope and marine carbon cycle changes during the last glacial-interglacial cycle[END_REF][START_REF] Howe | North Atlantic Deep Water Production during the Last Glacial Maximum[END_REF]. The NADW southern extension seems limited during glacial times, whereas southern-born water-masses extended further north [START_REF] Kuhn | Late Quaternary variability of ocean circulation in the southeastern South Atlantic inferred from the terrigenous sediment record of a drift deposit in the southern Cape Basin (ODP Site 1089)[END_REF][START_REF] Skinner | North Atlantic versus Southern Ocean contributions to a deglacial surge in deep ocean ventilation[END_REF]. Similarly, modifications of the Antarctic Circumpolar Current (ACC, including the CDW) during the last climatic cycle are still debated. Some studies reported severe modifications of the ACC intensity in the Atlantic [START_REF] Noble | Greater supply of Patagonian-sourced detritus and transport by the ACC to the Atlantic sector of the Southern Ocean during the last glacial period[END_REF] and Indian [START_REF] Dezileau | Evidence for strong sediment redistribution by bottom currents along the southeast Indian ridge[END_REF][START_REF] Mazaud | Variations of the Antarctic Circumpolar Current intensity during the past 500 ka[END_REF] sectors of the Southern Ocean: the activity of the ACC increased during the LGM, probably linked to enhanced westerly winds [START_REF] Dezileau | Evidence for strong sediment redistribution by bottom currents along the southeast Indian ridge[END_REF][START_REF] Walter | Provenance and transport of terrigenous sediment in the south Atlantic Ocean and their relations to glacial and interglacial cycles: Nd and Sr isotopic evidence[END_REF][START_REF] Mazaud | Variations of the Antarctic Circumpolar Current intensity during the past 500 ka[END_REF]. In contrast, other studies support insignificant modification of the ACC in the Atlantic sector of the Southern Ocean [START_REF] Gersonde | Last glacial sea surface temperatures and sea-ice extent in the Southern Ocean (Atlantic-Indian sector): A multiproxy approach[END_REF] and Drake Passage [START_REF] Mccave | Minimal change in Antarctic Circumpolar Current flow speed between the last glacial and Holocene[END_REF]. Finally, the evolution of the AABW is also uncertain. [START_REF] Krueger | North Atlantic Deep Water and Antarctic Bottom Water variability during the last 200ka recorded in an abyssal sediment core off South Africa[END_REF] suggests that the production of AABW was similar during glacial and interglacial, but dropped during terminations (including the last deglaciation). In addition, [START_REF] Menviel | Poorly ventilated deep ocean at the Last Glacial Maximum inferred from carbon isotopes: A data-model comparison study[END_REF] suggest that the "AABW" (corresponding to CDW and AABW in our study) was weaker during the LGM than today. In contrast, other studies suggest enhanced northward flow of AABW via deep western boundary currents in all three major ocean (Pacific: [START_REF] Hall | Intensified deep Pacific inflow and ventilation in Pleistocene glacial times[END_REF][START_REF] Govin | Evidence for northward expansion of Antarctic Bottom Water mass in the Southern Ocean during the last glacial inception[END_REF]Indian: Govin et al., 2009;Atlantic: Govin et al., 2009;[START_REF] Spooner | Grain Size Constraints on Glacial Circulation in the Southwest Atlantic[END_REF].

Any modifications of the AMOC have a potential effect on carbon storage/outgassing that is tightly controlled by ocean stratification/ventilation, itself resulting from contrasting physical and chemical properties of the water-masses. High ocean stratification -as during the last glacial -inhibits vertical mixing and isolates the deep ocean from the atmosphere. In contrast, ventilation events -breakdown of the stratification that occurred during the last deglaciation -allow CO 2 to upwell from the deep ocean and to be rapidly transferred to the atmosphere [START_REF] Toggweiler | Midlatitude westerlies, atmospheric CO2, and climate change during the ice ages[END_REF][START_REF] Barker | Extreme deepening of the Atlantic overturning circulation during deglaciation[END_REF][START_REF] Skinner | Ventilation of the Deep Southern Ocean and Deglacial CO2 Rise[END_REF][START_REF] Skinner | North Atlantic versus Southern Ocean contributions to a deglacial surge in deep ocean ventilation[END_REF][START_REF] Skinner | Radiocarbon evidence for alternating northern and southern sources of ventilation of the deep Atlantic carbon pool during the last deglaciation[END_REF][START_REF] Burke | The Southern Ocean's Role in Carbon Exchange During the Last Deglaciation[END_REF].

B. Geological setting

The Atlantic sector of the Southern Ocean may receive sediments from Antarctica, the Scotia Sea area (i.e., Scotia Arc, southern Patagonia, and northern Antarctic Peninsula) South America, and Africa. Here, we present the general geological structure of these areas, and their respective isotopic signatures (figure 1).

Antarctica corresponds to two distinct geological domains: East and West Antarctica.

West Antarctica includes the Ellsworth Mountains (EM), the Antarctic Peninsula (Ant P), the Scotia Arc region (SCA). The geology of the Ellsworth Mountains (figure 1) is poorly known due to the lack of outcrop. These mountains are composed of Precambrian rocks, corresponding mainly to granodiorite orthogneiss intruded by granitic and pegmatitic sheets [START_REF] Tingey | The geology of Antarctica[END_REF]. The isotopic composition of the area is not known, but the age of the rock suggests radiogenic Sr and Pb isotope ratios, and unradiogenic ε Nd (figure 1). This area mostly delivers illite to the sea [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF]; figure 1). The Antarctic Peninsula, composed of alkaline and calcalkaline magmatic rocks associated with deformed sediments of similar composition [START_REF] Anderson | Bedrock geology of Antarctica: A summary of exploration, 1831-1962[END_REF][START_REF] Tingey | The geology of Antarctica[END_REF], is a potential source of terrigenous sediment for CDW and AABW. The Antarctic Peninsula is characterized by radiogenic ε Nd , and low Sr and high Pb isotope ratios (figure 1). Clay minerals from this area mostly correspond to well-crystallized smectite (crystallinity around 1.5, Petschick et al., 1996; figure 1), and chlorite. The Scotia Arc islands rocks are similar to those of the Antarctic Peninsula but with slightly more radiogenic Nd, and slightly less radiogenic Sr and Pb (figure 1). This area exports exclusively well-crystallized smectite to the ocean (crystallinity lower than one; [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF].

The East Antarctic domain is an old shield with rocks > 0.9 Ga. Rocks from the Pensacola Mountains (PM) to the Shackleton Range (SR) represent the Ross Orogen (i.e., Transantarctic Mountains) and are mainly composed of varied metamorphic rocks aged from the Late Proterozoic to Late Paleozoic [START_REF] Barrett | The Devonian to Jurassic Beacon Supergroup of the Transantarctic Mountains and correlatives in other parts of Antarctica[END_REF][START_REF] Laird | The late Proterozoic-middle Palaeozoic rocks of Antarctica[END_REF][START_REF] Tingey | The regional geology of Archean and Proterozoic rocks in Antractica[END_REF]Hauptvogel and Passchier and references therein, 2012). The isotopic composition of the area is characterized by unradiogenic Nd, with intermediate to high Sr isotope ratios (figure 1). The Pb isotope composition unknown, as is the case for most of East Antarctica rocks. The few studies reporting Pb isotope ratios have been carried out on feldspars only. The area releases mostly illite and chlorite [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF]. Smectite is also exported from the Berkner Island, but is found only locally (Petschik et al., 1996). To the east, the Grenville Belts (920 to 1330 Ma) outcrop on the Coats Land (CL) and western Dronning Maud Land (WDML) with a wide range of gneissic and clastic sediments [START_REF] Capurro | Expedición argentina al Mar de Weddell, diciembre de 1954 a enero de 1955[END_REF][START_REF] Anderson | Bedrock geology of Antarctica: A summary of exploration, 1831-1962[END_REF][START_REF] Tingey | The geology of Antarctica[END_REF] with unradiogenic Nd, and radiogenic Sr isotope ratios (figure 1). Clay minerals produced in this area are mainly chlorite and illite [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF]. In the northernmost part of the Dronning Maud Land, the old Grunehogna Craton is composed mainly of Archean granitoids [START_REF] Tingey | The geology of Antarctica[END_REF][START_REF] Mieth | Banded iron formation (?) at Grunehogna Craton, East Antarctica -Constraints from aeromagnetic data[END_REF][START_REF] Pierce | A comparison of detrital U-Pb zircon, 40Ar/39Ar hornblende, 40Ar/39Ar biotite ages in marine sediments off East Antarctica: Implications for the geology of subglacial terrains and provenance studies[END_REF] with very unradiogenic Nd (ε Nd << -20) and radiogenic Sr ratios (figure 1). The clay minerals generated in that area are mainly chlorite and illite [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF].

South America can be divided into two blocks: the recent Andean Orogen, and the old South American Shield. In the Atlantic Sector of the Southern Ocean, the Andean Orogen mostly corresponds to Patagonia (Pat). The geology and the isotopic composition of this region is similar with the Antarctic Peninsula: radiogenic Nd, unradiogenic Sr and Pb isotope ratios, but with higher 207 Pb/ 204 Pb than the Antarctic Peninsula (figure 1; [START_REF] Olivero | A review of the geology of the Argentinian Fuegian Andes[END_REF]Sayago et al., 2001 and references therein;[START_REF] Smith | Isotopic constraints on the source of Argentinian loess -with implications for atmospheric circulation and the provenance of Antarctic dust during recent glacial maxima[END_REF][START_REF] Khondoker | New constraints on elemental and Pb and Nd isotope compositions of South American and Southern African aerosol sources to the South Atlantic Ocean[END_REF]. Even if the climate is slightly more humid than in the Antarctic Peninsula, Patagonia also produces mainly well-crystallized smectite [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF][START_REF] Desiage | Quantifying sources and transport pathways of surface sediments in the Gulf of San Jorge, central Patagonia (Argentina)[END_REF][START_REF] Khondoker | New constraints on elemental and Pb and Nd isotope compositions of South American and Southern African aerosol sources to the South Atlantic Ocean[END_REF].

The South American Shield is composed of several cratonic areas separated by vast ancient orogenic belts. [START_REF] Cordani | Crustal evolution of the South American Platform, based on Nd isotopic systematics on granitoid rocks[END_REF][START_REF] Engler | The Geology of South America[END_REF][START_REF] Oyhantçabal | The Río de la Plata Craton: a review of units, boundaries, ages and isotopic signature[END_REF][START_REF] Siegesmund | Multi-accretional tectonics at the Rio de la Plata Craton margins: preface[END_REF][START_REF] De Alkmim | Geological Background: A Tectonic Panorama of Brazil[END_REF]. Cratonic areas are mainly composed of granitoids and a wide range of metamorphic rocks, while orogenic belts are composed of a large variety of metamorphic rocks with high original composition (from the granite to the ophiolite and the juvenile magmatic arc; [START_REF] De Almeida | Brazilian structural provinces: An introduction[END_REF][START_REF] Barros | Ministério das Minas e Energia[END_REF][START_REF] Moura | Evidence of Brasiliano/Panafrican deformation in the Araguaia belt: implication for Gondwana evolution[END_REF][START_REF] Neves | Proterozoic history of the Borborema province (NE Brazil): Correlations with neighboring cratons and Pan-African belts and implications for the evolution of western Gondwana[END_REF][START_REF] De Alkmim | Geological Background: A Tectonic Panorama of Brazil[END_REF][START_REF] Nogueira | Carbon and strontium isotope fluctuations and paleoceanographic changes in the late Neoproterozoic Araras carbonate platform, southern Amazon craton, Brazil[END_REF][START_REF] Pimentel | The tectonic evolution of the Neoproterozoic Brasília Belt, central Brazil, based on SHRIMP and LA-ICPMS U-Pb sedimentary provenance data: A review[END_REF][START_REF] Fuck | Paleoproterozoic crust-formation and reworking events in the Tocantins Province, central Brazil: A contribution for Atlantica supercontinent reconstruction[END_REF][START_REF] Mcgee | Investigating mid-Ediacaran glaciation and final Gondwana amalgamation using coupled sedimentology and 40Ar/ 39Ar detrital muscovite provenance from the Paraguay Belt, Brazil[END_REF][START_REF] Silva | The Neoproterozoic-Cambrian Paraguay Belt, central Brazil: Part I -New structural data and a new approach on the regional implications[END_REF]. The overall isotopic composition of the South American Shield is radiogenic Sr and Pb, and very unradiogenic Nd isotope ratios (figure 1). South of the South American Shield, a large tholeiitic-basaltic province is known as the Parana basalt [START_REF] Waichel | Stratigraphy and volcanic facies architecture of the Torres Syncline, Southern Brazil, and its role in understanding the Paraná-Etendeka Continental Flood Basalt Province[END_REF][START_REF] Milani | Orogenias paleozóicas no domínio sul-ocidental do Gondwana e os ciclos de subsidência da Bacia do Paraná[END_REF]. The composition of the Parana basalts differs from the South American Shield with radiogenic Nd, and very low 87 Sr/ 86 Sr ratio (<0. 5;Tapani Ramo et al., 2016).

This South American Shield is drained by important riverine systems such as the Amazon and Parana rivers. The Amazon drains sediments from the Andes, as well as the South American Shield. The South American Shield is characterized by rocks with unradiogenic Nd and radiogenic Sr and Pb (figure 1). The clay mineral exported to the ocean is mainly kaolinite [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF][START_REF] Guyot | Clay mineral composition of river sediments in the Amazon Basin[END_REF][START_REF] Bayon | Rare earth elements and neodymium isotopes in world river sediments revisited[END_REF]. However, sediments are mainly exported northwards toward the Caribbean Sea. The Parana River drains the southern part of the South American Shield, the Parana basalts, and the north of Patagonia. Its isotopic composition has intermediate Nd, Sr, and Pb isotope ratios (figure 1).

Clay minerals transported via this river are illite (~60%; [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF][START_REF] Campodonico | The geochemical signature of suspended sediments in the Parana River basin: Implications for provenance, weathering and sedimentary recycling[END_REF], kaolinite, and smectite. Other smaller rivers drain the south of Brazil, and mainly deliver sediments characterized by unradiogenic Nd, and radiogenic Sr and Pb isotope ratios, containing mainly smectite derived from the Parana basalts and kaolinite (figure 1; [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF]. On the other hand, Patagonia and Pampas are dry and windy areas [START_REF] Clapperton | Quaternary geology and geomorphology of South America[END_REF]. Consequently, part of the detrital particles is exported to the ocean via aeolian processes as loess [START_REF] Mathias | Magnetic fingerprint of the late Holocene inception of the Río de la Plata plume onto the southeast Brazilian shelf[END_REF]. The overall isotopic composition of this smectiterich loess is radiogenic Nd, unradiogenic Pb and Sr ratios. According to [START_REF] Mathias | Magnetic fingerprint of the late Holocene inception of the Río de la Plata plume onto the southeast Brazilian shelf[END_REF], isotope ratios (figure 1). Clay minerals formed in the Congo depression are mainly poorly crystallized smectite and kaolinite, whereas the Namibian deserts release illite-rich loess [START_REF] Bremner | Mineralogy and geochemistry of the clay fraction of sediments from the Namibian continental margin and the adjacent hinterland[END_REF][START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF][START_REF] Bayon | Rare earth elements and neodymium isotopes in world river sediments revisited[END_REF]; figure 1).

III. Material and methods

A. Material

This study is based on sediment samples from core MD07-3076Q (44°9.2'S, 14°13.7'W) recovered by the French Vessel Marion Dufresne in 2007 on the eastern flank of the Mid-Atlantic Ridge at 3770 m depth (figure 1). The core chronology is based on planktonic foraminifer radiocarbon dates (30 measurements for the studied interval) and stratigraphic control points [START_REF] Skinner | Ventilation of the Deep Southern Ocean and Deglacial CO2 Rise[END_REF][START_REF] Skinner | North Atlantic versus Southern Ocean contributions to a deglacial surge in deep ocean ventilation[END_REF][START_REF] Skinner | Radiocarbon evidence for alternating northern and southern sources of ventilation of the deep Atlantic carbon pool during the last deglaciation[END_REF]Gottschalk et al, 2015b). Today, the site is bathed in the LCDW. From the seafloor to the surface, the water masses observed in the water column above the study site are the LCDW, NADW, UCDW, and intermediate and surface waters. In nearby deeper oceanic basins, the AABW is also found, and it is thought that particles transported by this bottom water can reach our site by advection and mixing with the LCDW.

B. Sample preparation and analytical procedure

All samples were first decarbonated using 0.1N HCl and then deflocculated by repeated washing using pure water.

1.

Grain-size distribution

Grain-size distribution was measured on carbonate-free sediment using a Malvern Mastersizer 2000 laser (0.02-2000 µm) following standard protocols [START_REF] Montero-Serrano | Sedimentary evidence of deglacial megafloods in the northern Gulf of Mexico (Pigmy Basin)[END_REF]. The clay-size fraction corresponds to the proportion (in volume) of particles with a diameter smaller than 2 µm, the cohesive silts correspond to the 2 to 10 µm diameter particles, the sortable silts correspond to the 10 to 63 µm diameter particles, and the sand fraction to the particles coarser than 63 µm.

Clay mineralogy

The clay-size fraction (< 2µm) was isolated by differential settling according to Stoke's Law. This fraction was then concentrated by centrifugation (40 minutes, 3500 rotation per minute) and an aliquot was placed on glass slides. X-ray diagrams were obtained using a Bruker D4Endeavor (standard 30 kV and 30 mA). Each sample is run three times between 2.49 and 32.5°2θ: (1) dried sample, (2) glycolated sample (12 hours in ethylene glycol), and

(3) heated sample (490°C for 2 hours). The proportion of each clay mineral (smectite, chlorite, illite, and kaolinite) is determined using the main X-ray diffraction peaks (layer and interlayer) on X-ray spectra according to their crystallographic characteristics [START_REF] Brown | X-ray diffraction procedures for clay mineral identification[END_REF].

Smectite is characterized by a main peak at 14-15 Å on the air-dried samples that expands at 17 Å after ethylene glycol saturation and collapses at 10 Å after heating. Illite is characterized by a main peak at 10 Å on the three runs. Kaolinite and chlorite are measured based on their main peak at 7-7.2 Å and further distinguished using pseudo-void deconvolution of the kaolinite/chlorite doublet at 3.54/3.58 Å. All measurements and semi-quantitative estimations are processed using the McDiff software (Petschick, 2000). The index of Esquevin [START_REF] Esquevin | Influence de la composition chimique des illites sur leur cristallinité[END_REF] corresponds to the ratio between the intensity of the peak of illite at 5 Å and at 10 Å (illite 5Å/10Å). In this study, the crystallinity of illite and smectite has been measured using the method of integral breath to enable comparison with the work of Petschik et al. (1996) in the South Atlantic. High crystallinity (high values of the index) corresponds to badly crystallized mineral.

Isotope Analysis

The grain-size distribution recognized three distribution modes. These three grain-size fractions were then isolated in order to examine their provenance. The clay-size fraction (0-2 µm) was isolated by repeated extractions by settling. The coarse fraction (20-40 µm in the old section of the core before 11.5 ka cal BP, noted hereafter as ka, and 20-32 µm after 11.5 ka) was isolated by sieving the clay-free residue. The 2-20 µm grain-size fraction is thus the residue of clay separation and coarse fraction sieving. An aliquot of 10 to 150 mg (depending of the sediment quantities available) was then used for chemical procedures.

Chemical and isotopic measurements were performed at the Faculty of Science of the Vrije Universiteit, Amsterdam. Sediment was digested in closed Savillex TM Teflon beakers using a mixture of concentrated HF and HNO 3 (~2/3 and 1/3, respectively) for a few days at 120°C. After digestion, samples were dried out and re-dissolved in ~6.5N HCl to remove fluorides. Nd, Sr, and Pb were purified using conventional ion chromatography. Pb isotopes were processed first and purified using AG-X8 200-400 mesh resin. Light rare earth elements (LREE) were isolated using true-spec resin medium (Eichrom TM , 100-150 µm mesh size) and Nd was eluted from the LREE fraction using LN-resin (Eichrom TM , 50-100 µm mesh size). Sr was recovered using Sr resin column. Nd and Pb measurements were performed by bracketing using respectively CIGO and NBS981 standards on Thermo Scientific Neptune multicollector inductive coupled plasma-mass spectrometer (MC-ICPMS), whereas Sr measurements were performed on a thermal ionization multi-collector-MS (TIMS). Due to relatively low content of Nd in some of the coarse grain-size fraction (20-32/40µm), Nd measurements of these fractions were also performed by TIMS.

IV. Results

A. Grain-size distribution

Grain-size results from core MD07-3076Q. The grain-size distribution is bimodal throughout the core (figure 2) with a coarse mode ranging in the sortable silts fraction (from 23.6 and 36.2 µm, average: 30.4, standard deviation: 2.48; table 1) and a fine mode ranging in the cohesive silts fraction (from 5.6 and 9.3 µm, average: 6.8, standard deviation: 0.8; table 1). The sortable silt (10-63 µm) fraction is dominant (41 to 52% in volume of the total terrigenous fraction, average: 47%, standard deviation: 2.4; table 1) and the cohesive silts (2-10 µm) represent 35 to 45% (average: 39%, standard deviation: 2.4; table 1). The clay (<2 µm) and sand fractions (>63 µm) represent respectively 2 to 5% (average: 3.4%, standard deviation: 0.7; table 1) and 1 to 6% (average: 3.0, standard deviation: 1.0; table 1) of the total terrigenous fraction (table 1).

In details, the mean of the coarse mode (hereafter mentioned as the sortable silt mode) is slightly coarser during the LGM (figure 2

B. Clay Mineralogy

The clay mineral assemblage is composed of smectite ((S) 18-59%; figure 3 The K/C ratio is stable during the LGM, and increases during the deglaciation. The I/S ratio presents two maxima at the beginning of the record and at the end of the LGM, sharply decreases at the beginning of the HS 1, and steadily decreases during the deglaciation.

Crystallographic properties of illite from site MD07-3076Q (black dots) and Figure 4: comparison with properties of illite from potential sources to the South Atlantic basin. The data used for comparison are from [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF]. Illite 5Å/10Å ratio gives information on the chemical properties of illite (Fe-Mg-vs Al-rich illite) while the crystallinity gives clues on the quality of the mineral crystal (high crystallinity: badly crystallized mineral).

C. Radiogenic Isotopes

Isotopic results are presented for the sortable silt mode fraction (20-32/40 µm) and the cohesive silt mode fraction (2-20 µm) and for the clay-size fraction (<2 µm) (tables 2 to 4).

Lead isotope ratios were only been measured on the clay-size fraction (table 2).

1.

Clay-size fraction (<2 µm)

The ε Nd of the clay-size fraction ranges from -7.2 to -4.8. It is relatively stable during the last glacial (<± 0. We note that the Sr isotope rebound observed at 12.7 ka is also associated with variations Pb isotope ratios.

2.

Cohesive silt mode fraction (2-20 µm)

The ε Nd of the 2-20 µm grain-size fraction (cohesive silt mode fraction) ranges from -5.5 to -3.9 with the lowest values at 13, 18, 23 and 29 ka (figure 5.b). The 87 Sr/ 86 Sr ratios are generally constant with higher values around 13, 19, and 24 ka (figure 5.f).

3.

Sortable silt mode fraction: (20-32/40 µm)

The ε Nd of the sortable silt mode fraction ranges from -4.9 to -1.4. Values are relatively unchanging during the last glacial period (-2 ± 0.5 ε Nd ) but decreases after 18 ka and reaches a minimum (-5) at the end of the deglaciation (figure 5.a). The 87 Sr/ 86 Sr ratio ranges from 0.708 and 0.710. 87 Sr/ 86 Sr values are lower during the HS 2, at the beginning of the HS 1, and at the beginning of the YD, while the highest value is recorded at the B-A offset (figure

5.e).

Isotopic results from core MD07-3076Q. (a) ε Nd from the sortable silt mode

V. Discussion

A.

Sediment provenance

1.

Clay size fraction: an overall provenance signal

To determine the provenance of this grain-size fraction, both clay mineral proportions and radiogenic isotopes have been used. Kaolinite and chlorite have distinct provenances: at present, kaolinite is mainly found at low latitudes where chemical weathering is strong.

Brazilian rivers (Amazon and Parana), as well as equatorial and tropical African rivers are characterized by high contents of kaolinite (figure 1). Inherited kaolinite is also found in East

Antarctica marine sediments (figure 1), but is transported by the westward Antarctic Coastal

Current and remains trapped in the Weddell-Enderby Basin due to the Weddell Gyre circulation [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF] and this kaolinite is therefore unlikely to contribute to sedimentation at the studied site. Consequently, kaolinite can be used to trace the low latitude provenance. Conversely, presently, chlorite mainly characterizes high latitude regions, where weak chemical weathering allows its preservation. It is abundant in Antarctica and the Scotia Sea (figure 1). Consequently, chlorite can be considered a tracer of high latitude provenance.

Thus, the kaolinite/chlorite ratio (K/C) discriminates southern-born versus northern-born material in the southern Atlantic [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF][START_REF] Kuhn | Late Quaternary variability of ocean circulation in the southeastern South Atlantic inferred from the terrigenous sediment record of a drift deposit in the southern Cape Basin (ODP Site 1089)[END_REF]Kruger et al., 2008).

Illite provenance is more complex. It is very abundant in the Weddell Sea, Namibian deserts, the Parana River (60% of the delivered sediment), and it is also present, although at lower concentrations (<30%), in the Scotia Sea (figure 1). To decipher the provenance of illite, we used the chemical (5/10Ǻ ratio, i.e., Fe-Mg vs. Al rich illite) and crystallographic properties (crystallinity) of this mineral. Data are compared with the 5/10Ǻ ratio and the crystallinity of illite of potential illite sources from the database of [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF] (figure 4). This comparison demonstrates that the illite from core MD07-3076Q is similar to illite from the Weddell and Scotia seas while the chemical and crystallographic properties of the illite recovered at site MD07-3076Q is not compatible with a Namibian source. In the Scotia Sea, illite represents less than 30% of the total clay mineral fraction (from 10-30%; [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF] and represents a mix of illite coming from the Weddell Sea embayment via the AABW, and illite from the Pacific sector of Antarctica delivered by the CDW [START_REF] Diekmann | Terrigenous sediment supply in the Scotia Sea (Southern Ocean): response to Late Quaternary ice dynamics in Patagonia and on the Antarctic Peninsula[END_REF][START_REF] Walter | Provenance and transport of terrigenous sediment in the south Atlantic Ocean and their relations to glacial and interglacial cycles: Nd and Sr isotopic evidence[END_REF][START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF]. Importantly, in the Weddell Sea, illite represents at least 50% of the total clay mineral fraction (more than 80% in some areas; [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF]. Consequently, the Weddell Sea embayment is considered as the major, source of illite for our studied site.

Smectite has several potential provenances: the Angola Basin, southern South America, Scotia Sea Islands, and Antarctic Peninsula. The crystallinity of this mineral was measured in order to decipher its provenance. The well-crystallized smectite (low crystallinity; figure 3) is compatible with a provenance from southern South America (Pampas and Patagonia), Scotia Arc, or Antarctic Peninsula, which are all characterized by crystallinity lower than 1.5 [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF]; figure 3). It rules out a contribution of poorly crystallized smectite (crystallinity > 2; [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF] from Angola. In detail, the crystallinity of the smectite from our studied site likely corresponds to a mix between two Data sources: -South American Shield-Allegre et al. (1996); [START_REF] Basile | Patagonian origin of glacial dust deposited in East Antarctica (Vostok and Dome C) during glacial stages 2, 4 and 6[END_REF]; [START_REF] Walter | Provenance and transport of terrigenous sediment in the south Atlantic Ocean and their relations to glacial and interglacial cycles: Nd and Sr isotopic evidence[END_REF]; de [START_REF] De Mahiques | Nd and Pb isotope signatures on the Southeastern South American upper margin: Implications for sediment transport and source rocks[END_REF]; [START_REF] Jeandel | Isotopic Nd compositions and concentrations of the lithogenic inputs into the ocean: A compilation, with an emphasis on the margins[END_REF], and references therein; [START_REF] Mallmann | Isotope geochemistry and geochronology of the Nico Pérez Terrane, Rio de la Plata Craton, Uruguay[END_REF]; Ganade [START_REF] Ganade De Araujo | Tracing Neoproterozoic subduction in the Borborema Province (NE-Brazil): Clues from U-Pb geochronology and Sr-Nd-Hf-O isotopes on granitoids and migmatites[END_REF]; [START_REF] Fuck | Paleoproterozoic crust-formation and reworking events in the Tocantins Province, central Brazil: A contribution for Atlantica supercontinent reconstruction[END_REF]; -Patagonia, Pampas, Southern Andes- [START_REF] Stern | Traceelement and Sr, Nd, Pb, and O isotopic composition of Pliocene and Quaternary alkali basalts of the Patagonian Plateau lavas of southernmost South America[END_REF]; [START_REF] Grousset | Origins of peri-Saharan dust deposits traced by their Nd and Sr isotopic composition[END_REF]; [START_REF] Basile | Patagonian origin of glacial dust deposited in East Antarctica (Vostok and Dome C) during glacial stages 2, 4 and 6[END_REF]; [START_REF] Walter | Provenance and transport of terrigenous sediment in the south Atlantic Ocean and their relations to glacial and interglacial cycles: Nd and Sr isotopic evidence[END_REF]; [START_REF] Smith | Isotopic constraints on the source of Argentinian loess -with implications for atmospheric circulation and the provenance of Antarctic dust during recent glacial maxima[END_REF]; [START_REF] Jeandel | Isotopic Nd compositions and concentrations of the lithogenic inputs into the ocean: A compilation, with an emphasis on the margins[END_REF], and references therein; [START_REF] Khondoker | New constraints on elemental and Pb and Nd isotope compositions of South American and Southern African aerosol sources to the South Atlantic Ocean[END_REF]; -Scotia Arc and Ridge- [START_REF] Jeandel | Isotopic Nd compositions and concentrations of the lithogenic inputs into the ocean: A compilation, with an emphasis on the margins[END_REF]; [START_REF] Harrison | Resolving mantle components in oceanic lavas from segment E2 of the East Scotia back-arc ridge, South Sandwich Islands[END_REF];-Antarctic Peninsula- Hole el al. (1993); Kosler et al. (2009); [START_REF] Roy | 40Ar/39Ar ages of hornblende grains and bulk Sm/Nd isotopes of circum-Antarctic glacio-marine sediments: Implications for sediment provenance in the southern ocean[END_REF]; [START_REF] Lee | Geochemical characteristics and the provenance of sediments in the Bransfield Strait, West Antarctica[END_REF]; -East Antarctica-DePaolo et al. (1982); [START_REF] Luttinen | Neodymium and strontium isotopic and trace element composition of a Mesozoic CFB suite from Dronning Maud Land, Antarctica: implications for lithosphere and asthenosphere contributions to Karoo magmatism[END_REF][START_REF] Luttinen | Björnnutane and Sembberget basalt lavas and the geochemical provinciality of Karoo magmatism in western Dronning Maud Land, Antarctica[END_REF]; [START_REF] Roy | 40Ar/39Ar ages of hornblende grains and bulk Sm/Nd isotopes of circum-Antarctic glacio-marine sediments: Implications for sediment provenance in the southern ocean[END_REF]; [START_REF] Will | Geochemical and isotopic constraints on the tectonic and crustal evolution of the Shackleton Range, East Antarctica, and correlation with other Gondwana crustal segments[END_REF].

The coupled ε Nd -87 Sr/ 86 Sr isotope variation of the clay-size fraction (figure 6) reveal a mixed provenance between young sources around the Scotia Sea (Scotia Arc, Antarctic Peninsula, Patagonia) and southern South America (Patagonia and Pampas), and an old source from East Antarctica or the South American Shield (i.e., Brazil and Parana River). 2018), -Patagonia-; [START_REF] Cohen | Identification of recycled continental material in the mantle from Sr, Nd and Pb isotope investigations[END_REF]; [START_REF] Barreiro | Lead isotopic compositions of South Sandwich Island volcanic rocks and their bearing on magmagenesis in intra-oceanic island arcs[END_REF], -Scotia Arc-; [START_REF] Lee | Geochemical characteristics and the provenance of sediments in the Bransfield Strait, West Antarctica[END_REF], Kosler et al. (2009), Flowerdew et al. ( 2012) -Antarctic Peninsula-, de Mahiques et al. (2007), -South American Shield-; [START_REF] Flowerdew | Distinguishing East and West Antarctic sediment sources using the Pb isotope composition of detrital K-feldspar[END_REF], -Eastern Weddell Sea-.

Pb isotope composition of core MD07-3076Q and of potential sources of

The coherent Pb isotope variations in figure 7 support this interpretation recording a mix between the Antarctic Peninsula, Scotia Arc, and South American Shield. However, since very few data are available for the Pb isotope compositions of East Antarctica, a contribution from this area cannot be excluded. The three isotopic systems suggest an increased contribution of older material during the deglaciation compared with the LGM. Based solely on Nd and Pb isotope data, it is rather difficult to distinguish South America and East Antarctica as the old end-members during the deglaciation. However, the increase of the K/C ratio during the deglaciation supports the hypothesis of enhanced relative contribution from the South American Shield.

2.

Cohesive silt mode fraction (2-20 µm)

Both 87 Sr/ 86 Sr and ε Nd of the cohesive silt mode fraction record limited variation throughout the deglaciation (figure 5). The isotopic results indicate that the provenance is located in Patagonia and in the Antarctic Peninsula, with an additional contribution of old source (South American Shield and/or East Antarctica). These results suggest that no major modification of provenance occurred during the deglaciation. Strontium and Nd isotope ratios do not allow discrimination of the source of old material for the cohesive silt mode fraction.

The Nd isotope ratios suggest on average a higher radiogenic contribution for cohesive silts compared with the clay-size fraction (figure 6).

3.

Sortable silt mode fraction (20-32/40 µm)

Both Sr and Nd isotope ratios of the sortable silt during the LGM record one dominant provenance: the Scotia Sea area (Patagonia, Scotia Arc, Antarctic Peninsula; figure 5). During the deglaciation, an important shift to less radiogenic ε Nd values (4 units) is observed implying an increased contribution of an older end-member such as East Antarctica and/or the South American Shield. However, because East Antarctica and the South American shield have similar Sr and Nd isotope composition, it is not possible to distinguish them with these isotopes (figure 6). Consequently, investigating the main transportation patterns is necessary to identify the source of old material for both the cohesive (2-20 µm) and the sortable silt mode fractions (20-32/40 µm).

In summary, (figure 6) all three grain-size fractions compositions are located between two end-members: the Scotia Sea-southern South America area (Antarctic Peninsula, Scotia Arc and Ridge, Patagonia, Pampas, Southern Andes), and crustal shields (East Antarctica, South American Shield). The clay-size fraction appears the most crustal-like, whereas the sortable silt mode presents the most mantle-like composition. The 2-20 µm grain-size fraction presents the lowest 87 Sr/ 86 Sr, meaning that the difference with the other grain size fraction is related to distinct provenances rather than grain size effect. Both the clay size and the sortable silt mode fractions display an increase of the crustal end-member. In the clay size fraction, clay mineralogy enabled the identification of this old crustal source (i.e., the South American Shield).

B. Transportation pattern and palaeoclimatic implications

The provenances of the sediments for the three distinct grain-size fractions have been identified (or partially identified) in the previous section using their mineralogical and geochemical characteristics. Now, we will focus on identifying their transportation patterns and vectors from the source to the sedimentation site.

Several studies propose that aeolian processes may lead to significant particle transfers from Patagonia into the central Atlantic sector of the Southern Ocean [START_REF] Hegner | Nd isotopic constraints on the origin of suspended particles in the Atlantic Sector of the Southern Ocean[END_REF][START_REF] Desiage | Quantifying sources and transport pathways of surface sediments in the Gulf of San Jorge, central Patagonia (Argentina)[END_REF]. The aeolian contribution of loess from Patagonia was enhanced during the LGM as far as Antarctica (Petit et al., 1990;[START_REF] Grousset | Origins of peri-Saharan dust deposits traced by their Nd and Sr isotopic composition[END_REF][START_REF] Diekmann | Sedimentary patterns in the late Quaternary Southern Ocean[END_REF][START_REF] Lambert | Dust-climate couplings over the past 800,000 years from the EPICA Dome C ice core[END_REF]. Although this hypothesis could be supported by the radiogenic Nd signal observed in both the clay-size and the sortable silt mode fraction during the LGM, the mineralogical of MD07-3076Q sediments is not in agreement with an enhanced contribution from Patagonia. The dominant clay mineral in Patagonia is smectite (up to 95%), and the contribution of Patagonian smectite in our clay-size fraction is lowest during the LGM (figure 3). Consequently, direct aeolian inputs cannot be significant at our site, and oceanic currents appear to be the main contributors to sedimentation [START_REF] Moriarty | Clay minerals in Southeast Indian Ocean sediments, transport mechanisms and depositional environments[END_REF][START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF][START_REF] Kuhn | Late Quaternary variability of ocean circulation in the southeastern South Atlantic inferred from the terrigenous sediment record of a drift deposit in the southern Cape Basin (ODP Site 1089)[END_REF]. This means that any aeolian particles from Patagonia delivered to the southwest Atlantic [START_REF] Mathias | Magnetic fingerprint of the late Holocene inception of the Río de la Plata plume onto the southeast Brazilian shelf[END_REF] likely reach our site via oceanic transport processes.

The size of particles transported by water flow is directly related to the flow energy, with size increasing with the flow speed. This property was used in previous studies to track the temporal evolution of paleo-current flow (e.g. [START_REF] Mccave | Size sorting in marine muds: Processes, pitfalls, and prospects for paleoflow-speed proxies: SIZE SORTING IN MARINE MUDS[END_REF][START_REF] Mccave | Distinguishing current effects in sediments delivered to the ocean by ice. I. Principles, methods and examples[END_REF]. Below we show that the different grain-size modes not only correspond to distinct flow speeds, but specific water mass at site MD07-3076Q. Consequently, grain-size modes (2-20 µm and 20-32/40 µm) can be associated to specific deep-water-masses.

The clay-size fraction (i.e., the < 2 µm particles) with very high specific surface readily floats and hence can undergo long-range transportation (>500 km). Consequently, particles within this grain-size fraction can be used to record the relative contribution of the main deep-water masses.

1.

Clay-size fraction: the distant terrigenous signal

The NADW carries fine suspended particles from as far as the Labrador Sea.

However, this signal is probably overprinted by the supply of sediments from more proximal sources such as Africa or South America. The western branch of the NADW (NADW-W; i.e.,

Deep Western Boundary Current) can transport sediments from Brazil, Parana River, Pampas, and Patagonia (figure 1). Both mineralogical and geochemical compositions of the particles transported by the western branch of the NADW are likely controlled by the southern extension of the water-mass. Currently the western branch drifts away from the South American coast around 45°S. This southern extension likely changed during the last glacial period and deglaciation [START_REF] Skinner | Ventilation of the Deep Southern Ocean and Deglacial CO2 Rise[END_REF][START_REF] Skinner | Radiocarbon evidence for alternating northern and southern sources of ventilation of the deep Atlantic carbon pool during the last deglaciation[END_REF]Vasquez-Riveiros et al., 2010;[START_REF] Waelbroeck | The timing of deglacial circulation changes in the Atlantic[END_REF]Gottschalk et al., 2015a,b;[START_REF] Howe | North Atlantic Deep Water Production during the Last Glacial Maximum[END_REF]. Depending on its southern extent, the NADW is thus able to carry either mostly kaolinite (equatorial Brazil), or kaolinite and smectite (southern Brazil), or illite (Parana River basin), or well-crystallized smectite (crystallinity ~1.5; Patagonia). As shown above, the ε Nd signature of these sediments is more radiogenic when the NADW extends further south (-20 in equatorial Brazil, to ~0 in Patagonia) while the Pb and Sr yield a slightly less radiogenic signature (figures 6 and 7).

The CDW transports sediments from the Scotia Sea area, including Scotia Arc, Patagonia, and the Antarctic Peninsula, as well as from the Weddell Sea when mixing occurs between the lower part of the LCDW and AABW. Then particles transported by the CDW likely record a younger isotopic signature (i.e., more radiogenic ε Nd and unradiogenic Sr and Pb isotopes), and a mineralogical composition dominated by smectite and chlorite, while additional contribution of old material (unradiogenic ε Nd and radiogenic Sr and Pb isotopes)

and illite is possible when the LCDW and AABW mix together. In summary, illite is considered as injected into the sedimentary system via the AABW through mixing processes between LCDW and AABW while smectite and chlorite are likely transported by the CDW.

The AABW in the Atlantic sector mainly forms in the Weddell Sea embayment [START_REF] Orsi | Circulation, mixing, and production of Antarctic Bottom Water[END_REF], and thus, must carries sediments from its drainage basin (East Antarctica, Antarctic Peninsula), but may also transport sediment winnowed on its pathway such as the Consequently, the composition of particles transported by the AABW flowing out of the Weddell Sea is intermediate, with ε Nd around -9 [START_REF] Walter | Provenance and transport of terrigenous sediment in the south Atlantic Ocean and their relations to glacial and interglacial cycles: Nd and Sr isotopic evidence[END_REF], and is potentially enriched in young material when entering the Scotia Sea.

The above observations are summarized in table 5, in which specific isotopic and mineralogical signatures are associated to each deep water mass. It is clear that the K/C ratio as well as the ε Nd composition reflect northern-versus southern-born water mass contributions (i.e., NADW versus CDW and AABW). Similarly, smectite and illite are transported by distinct water-masses and the illite/smectite ratio (I/S) can efficiently distinguish the AABW from the other water-masses. Thus, this ratio will further be used as a tool for estimating the AABW contribution through time. As a result, the contribution of NADW to the deposition of clay particles is underestimated (~10%) at the end of the deglaciation while the contribution of the CDW is overestimated (~10%). This choice does not have a strong impact on the contribution of the AABW (less than 4.5%). Second, the percentage of the contribution of each water mass is calculated by bringing the sum of the weights computed to 100:

[NADW's contribution] = W NADW /(W NADW + W CDW + W AABW ) x 100
To test the validity of this method to reconstruct the evolution of the past deep circulation, we compared our results with those of other water-masses proxies (e.g. seawater ε Nd and δ 13 C). However, these latter methods proved incapable of distinguishing AABW from CDW. Consequently, we based the comparison on the proportion of the NADW compared to the southern sourced deep waters. Based on data from the same core, our estimates give comparable results to these two proxies (see table 6). This suggests that our approach successfully reconstructs the evolution of these three deep water masses. However, our estimate of the proportion of the NADW is higher than the estimate of [START_REF] Howe | North Atlantic Deep Water Production during the Last Glacial Maximum[END_REF] based on ε Nd . This discrepancy can be explained by two factors. First, we were unable to make corrections for concentration differences of particles in the three deep water masses (i.e., quantity of clay particles per volume of water) due to the large uncertainties involved. In addition, it is very likely that the NADW is more concentrated in clay particles than the AABW and CDW due to sediment source effect (e.g., dry East Antarctica below thick ice sheets vs. humid South America highly drained by equatorial rivers). Consequently, even though our tool successfully reconstruct the variations of the NADW, the contribution of NADW is probably overestimated. In other words, our estimate of NADW contribution to the clay deposition is likely higher than the proportion of NADW (in volume of water). Second, the choice of the end member for the seawater ε Nd of AABW+CDW made by Howe et al.

(2016) is debatable (-5.5 during the LGM, -8.5 during the Holocene). [START_REF] Skinner | North Atlantic versus Southern Ocean contributions to a deglacial surge in deep ocean ventilation[END_REF] used a compositional end-member between -5 and -2, which yields a better match with the isotopic composition of seawater Nd at our site (-5.5, Skinner et al., 2013). Therefore, the estimate of Howe et al. ( 2016) appears to underestimate the contribution of NADW at our site.

From 25 to 20 ka, the CDW is clearly dominant, with a contribution of 50% on average, while the NADW and AABW deliver 35% and 15% of the clay fraction, respectively. The highest contribution of the AABW is observed at the end of the LGM between 20 and 17.5 ka (27% in average, but up to 52% at 18 ka). During this interval, the NADW and CDW deliver respectively 34% and 39% on average. At the end of this period, the mineralogical composition of the fine sediments deposited at site MD07-3076Q suggests that the AABW was dominant. At the beginning of the deglaciation, between 17.5 and 15 ka (i.e., during HS 1), the clay mineral composition of core MD07-3076Q indicates a decreased relative contribution of the AABW end-member (15% on average) associated to an increase of the relative contribution of the CDW (49%) end-member. This observation of an increase of the CDW contribution is supported by the radiogenic ε Nd of the clay-size fraction and a 87 Sr/ 86 Sr close to the Scotia Arc composition (figures 5 and 6).

(a) Plot of kaolinite/chlorite vs illite/smectite ratios from core MD07-3076Q Figure 8: from 25 to 10 ka. The composition of deep-water masses has been determined using the data from [START_REF] Petschick | Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography[END_REF]. (b) Ternary diagram comparing the contribution of the three deep water masses to the clay deposition at site MD07-3076Q.

From 15 ka on, the clay mineral composition at the study site records an increasing contribution of the NADW until the end of the deglaciation (at least 47% for the interval 10-12 ka, figure 8). Compared with the LGM this suggests enhanced contribution of the NADW with reduced contributions from the CDW (40% for the interval 10-12 ka) and AABW (13% for the interval 10-12 ka). These results are strongly supported by the sharp decrease in ε Nd and by the concomitant increase of 208 Pb/ 204 Pb and 207 Pb/ 204 Pb ratios from the clay size fraction (figures 5 and 7). This corroborates the conclusions based on the cibicides δ 13 C measured in the same core (figure 9.e, [START_REF] Waelbroeck | The timing of deglacial circulation changes in the Atlantic[END_REF]. In addition, increasing inputs of less crystallized smectite (slightly higher crystallinity: ~1.5, supplementary figure S1) from Patagonia support the southward penetration of the NADW in the southern Atlantic Ocean, consistent with an increasing contribution of the NADW-W to sedimentation at site MD07-3076Q. Interestingly, the transition between B/A (that starts simultaneously with the southern Hemisphere cooling, the Antarctic Cold Reversal) and the YD appears to have no effect on the relative contribution of deep water masses and shows a continuous increase of the relative contribution of the NADW during these two periods.

Overall, the clay size fraction demonstrates that the contribution of the three deep water-masses changed through time. An increase of contribution of the AABW is recorded at the end of the LGM and is followed by a two-step deglaciation. First, an important reduction of the AABW is observed at the HS 1 onset. Second, an increase in the NADW contribution compared to the CDW is observed during the B/A and YD.

2.

Cohesive silt mode fraction (2-20 µm): an AABW signal According to our geochemical data, the provenance of the cohesive silt fraction is dominated by sources from the Scotia Sea area, especially Patagonia and Antarctic Peninsula, and by an old, unidentified, crustal source. According to the modern deep oceanic circulation, only the CDW and AABW are able to transport sediment from the Scotia Sea to the studied site (figure 1). It was also likely the case during the LGM and deglaciation. The AABW and CDW were likely spreading further north while the NADW was likely shallower, and retreated to the north [START_REF] Kuhn | Late Quaternary variability of ocean circulation in the southeastern South Atlantic inferred from the terrigenous sediment record of a drift deposit in the southern Cape Basin (ODP Site 1089)[END_REF][START_REF] Barker | Extreme deepening of the Atlantic overturning circulation during deglaciation[END_REF][START_REF] Waelbroeck | The timing of deglacial circulation changes in the Atlantic[END_REF]. These modifications do not affect the continental sources of terrigeneous sediment for the CDW and AABW compared the present day, and the NADW is still unable to transport sediments from the Scotia Sea. Consequently, it excludes the NADW as a transport medium for the cohesive silt mode fraction to site MD07-3076Q. Therefore, because the NADW is also the only water-mass able to transport sediment from the South American Shield to our study site, it excludes the South American Shield as a source of sediment for the cohesive silt mode fraction, and implies East Antarctica as the source of old material identified in the cohesive silt mode fraction. The terrigenous supplies deriving from East Antarctica/Scotia Sea strongly suggest the AABW has been the dominant carrier of the 2-20 µm grain-size fraction since the LGM. In addition, because the mean isotopic composition of this grain-size fraction transported by the AABW is relatively constant through time (figure 6), the relative contributions of East Antarctica and Scotia Sea area seem to have remained largely unchanged since the LGM.

3.

Sortable silt mode fraction (20-32/40 µm): A LCDW signal A part of the particles transported by the AABW and the NADW are derived from old crustal sources (i.e., East Antarctica and South American Shield, respectively). Thence, these two deep-water masses cannot be the source of the sortable silt mode fraction during the

LGM. In contrast, the CDW is a good candidate to transport particles solely from the Scotia Sea, as identified for the sortable silt mode fraction during the LGM. Consequently, the only possible source of this grain size fraction is the CDW. During the deglaciation, the Nd isotope composition of the sortable silt mode fraction became gradually less radiogenic while the 87 Sr/ 86 Sr ratio fluctuated, suggesting a modification of provenances and/or an additional contribution of less radiogenic Nd source. Such isotopic changes could be explained in two ways;

(1) a change in the CDW pathway;

(2) the incorporation of terrigenous material by mixing with other water-masses (such as AABW or NADW). The CDW slowed down and migrated southward during the deglaciation in concert with the southward migration of the subpolar and polar fronts [START_REF] Hole | Trace-element and isotopic characteristics of small-degree melts of the asthenosphere: Evidence from the alkalic basalts of the Antarctic Peninsula[END_REF][START_REF] Anderson | Wind-Driven Upwelling in the Southern Ocean and the Deglacial Rise in Atmospheric CO2[END_REF][START_REF] Denton | The Last Glacial Termination[END_REF]. However, such a change in the CDW pathway would have no effect on the terrigenous sources of particles. In contrast, several studies proposed increased ventilation in the Southern Ocean, enabling the degassing of oceanic CO 2 to the atmosphere [START_REF] Ahn | Atmospheric CO2 and Climate on Millennial Time Scales During the Last Glacial Period[END_REF][START_REF] Fischer | The role of Southern Ocean processes in orbital and millennial CO2 variations -A synthesis[END_REF][START_REF] Skinner | Ventilation of the Deep Southern Ocean and Deglacial CO2 Rise[END_REF][START_REF] Skinner | North Atlantic versus Southern Ocean contributions to a deglacial surge in deep ocean ventilation[END_REF][START_REF] Skinner | Radiocarbon evidence for alternating northern and southern sources of ventilation of the deep Atlantic carbon pool during the last deglaciation[END_REF][START_REF] Siani | Carbon isotope records reveal precise timing of enhanced Southern Ocean upwelling during the last deglaciation[END_REF]. Currently the base of the LCDW is mixed with the AABW, which was apparently not the case during the LGM [START_REF] Skinner | Ventilation of the Deep Southern Ocean and Deglacial CO2 Rise[END_REF]. The onset of AABW/LCDM mixing could explain the incorporation of unradiogenic terrigenous material from the Weddell Sea embayment (i.e., East Antarctica) into the LCDW. This mechanism likely explains the shift in ε Nd composition during the deglaciation. This hypothesis is supported by the results of [START_REF] Walter | Provenance and transport of terrigenous sediment in the south Atlantic Ocean and their relations to glacial and interglacial cycles: Nd and Sr isotopic evidence[END_REF] who reported lower ε Nd in terrigenous sediments in the southern Scotia Sea during the interglacial period and interpreted this as higher contribution of sediment from the Weddell Sea embayment due to the mixing of the AABW into the ACC. From 15 ka, the Nd isotope composition of the sortable silt mode fraction is very close to the one from the cohesive silt mode fraction transported by the AABW. It suggests that the sortable silt mode fraction is specifically transported by the LCDW rather than by the entire CDW. This highlights the fact that the ε Nd variations from the sortable silt mode fraction provide a useful tool to study the mixing 730 between the AABW and LCDW.

Comparison between paleoceanographic proxies from core MD07-3076Q and Figure 9: data produced in this study. Grey areas delimit the main climatic events and the red band highlights the particularly strong AABW event. (a) size of the sortable silt mode (µm), a proxy of the speed of the LCDW; (b) size of the cohesive silt mode (µm), a proxy of the speed of the AABW; (c) bottom water ventilation age from site MD07-3076Q (data from [START_REF] Skinner | Ventilation of the Deep Southern Ocean and Deglacial CO2 Rise[END_REF]; (d) ε Nd from the sortable silt size fraction; (e) Cibicides δ 13 C from site MD07-3076Q [START_REF] Waelbroeck | The timing of deglacial circulation changes in the Atlantic[END_REF]; (f) ε Nd from the cohesive silt size fraction; (g) seawater ε Nd from site MD07-3076Q [START_REF] Skinner | North Atlantic versus Southern Ocean contributions to a deglacial surge in deep ocean ventilation[END_REF]

b). On curves (h), (i) and

(j), the red line represent values calculated using the Holocene end-member of the NADW (I/S = 0.5), while the blue line correspond to the values calculated using the LGM end-member of the NADW (I/S = 1).

4.

Paleoceanographic implication

Our results establish that different grain-size modes can be attributed to distinct watermasses and that variation of the particle size of the different grain-size modes (figure 2) can be used to record the variations of flow speed of these water-masses as well as changes in pathways/mixing. This method has the advantage of distinguishing the speed of each water mass instead of giving the average speed of all the water masses, as it is the case for the sortable silt method [START_REF] Mccave | Size sorting in marine muds: Processes, pitfalls, and prospects for paleoflow-speed proxies: SIZE SORTING IN MARINE MUDS[END_REF]. During the last glacial period, the large mean particle diameter (>30 µm) of the sortable silt mode fraction reflects strong LCDW activity.

At the beginning of the deglaciation, the variation of the mean particle size suggests that the [START_REF] Mazaud | Variations of the Antarctic Circumpolar Current intensity during the past 500 ka[END_REF], with a notable increase from ~15 ka on (Mazaud et al., in prep.). Altogether, these studies and our results suggest that the weakening of the ACC started at ~15 ka.

From ~26 to 21 ka, the low particle sizes recorded in the cohesive silt mode (figure 2.b, transported by the AABW) indicate slow AABW, which is consistent with the observed moderate relative contribution of AABW in clay particles (figure 8 and9). In this time interval, one isolated high value is recorded at 24 ka and suggests that, temporarily, AABW activity was stronger. However, no change is registered in the clay minerals (figure 3 and9).

The grain-size data indicate that the AABW became more vigorous from 21 ka to reach its strongest speed at the end of the LGM. This maximum speed is concomitant with the strongest relative contribution of the AABW of the clay record (figures 3.h and 9), as shown by the peak of the illite/smectite ratio (figure 3) illustrated on figure 8. Interestingly, this AABW maximum preceded the HS 1, and both its speed and relative contribution fell at the

LGM/HS 1 transition as defined by [START_REF] Missiaen | Improving North Atlantic marine core chronologies using 230Th-normalization[END_REF]. At the beginning of the deglaciation, the abrupt decrease of the fine grain-size mode indicates a slowdown of the AABW (figure 2). This is supported by a sharp decrease in the illite/smectite ratio in the claysize fraction (figure 3), which also suggests an abrupt decrease of the relative contribution of Overall, the variations of the AABW flow speed and ventilation age are similar, with higher average speeds corresponding to the old ventilation ages. Taken together with the reconstructed vigorous LCDW during the LGM (figure 9.a.), these observations suggest that the deep Southern Ocean was poorly ventilated but with a vigorous circulation. It means that both the AABW and LCDW remained isolated from the surface during the LGM. This conclusion is consistent with our hypothesis that AABW was formed under ice shelves during this period and that the major expansion of sea ice [START_REF] Bianchi | Climate evolution at the last deglaciation: the role of the Southern Ocean[END_REF]Bostock et al., 2012;[START_REF] Adkins | The role of deep ocean circulation in setting glacial climates[END_REF]) kept the AABW isolated from the atmosphere during the LGM. In ε Nd between 17.5 and 16 ka, δ 13 C at 14.5 ka, δ 18 O at 15 ka, LCDW flow speed at 15 ka, NADW proportion at 15 ka) and also precedes the atmospheric CO 2 rise [START_REF] Bereiter | Revision of the EPICA Dome C CO2 record from 800 to 600 kyr before present[END_REF] and the change in the opal flux [START_REF] Anderson | Wind-Driven Upwelling in the Southern Ocean and the Deglacial Rise in Atmospheric CO2[END_REF]. For the first time, these data indicate a change in the deep Southern Ocean circulation that is associated with ventilation change that precedes the HS 1. This suggest that the identified large temporary (~1 kyr long) increase in the AABW contribution and flow speed may have had a substantial impact on the deep Southern Ocean ventilation, and by extension, on the deglacial CO 2 rise. Indeed, the magnitude of the change in the AABW behavior has the potential to "break" the hypothetical physical barrier between the deep Southern Ocean and the surface that was responsible of poorly ventilated deep water during the LGM. This combination of events also explains the unexpected early fall of the deep water ventilation age observed at ~18.2 ka.

Conclusion

The mineralogical characteristics of the clay-size fraction provide new insights into the general thermohaline circulation in the southern South Atlantic. The mineralogical signal demonstrates strong influence of both the CDW and AABW during the last glacial period.

Clay assemblages reveal a particularly high contribution of the AABW at the end of the

LGM, which is interpreted as reflecting strong Ice Shelf Mode bottom water production in the Weddell Sea. The contribution of the CDW and AABW then progressively decreases during the deglaciation together with the growing influence of the NADW (figure 8). Indeed, clay size fraction data monitor the progressive incursion of NADW into the Southern Ocean during the deglaciation from ~15 ka (figure 8), as well as the synchronous southward retreat of the southern-born deep water-masses (i.e., CDW and AABW).

The isotopic compositions of the distinct grain size modes provides invaluable information. The sortable silt mode fraction helps to trace the LCDW activity whereas the cohesive silt mode fraction is associated with the AABW signal. Consequently, the temporal evolution of flow speeds, pathways and interactions of these deep water-masses can be determined in a very robust way. This study suggests: Finally, this study demonstrates that based on (1) the combination of isotopic and mineral investigation of the clay size fraction, (2) the combination of isotopic measurement of isolated grain size modes and of grain size distribution results, and (3) a complete synthesis of the potential sources of sediments, it is possible to obtain reliable information on the lithogenic material transported by each deep water mass. This approach allows efficient tracking of the evolution of distinct water-masses through time, since it helps to isolate the specific signal associated to each water-mass. Based on these observations, we conclude that the increase in the AABW strength at the end of the LGM may have had a substantial impact on the ventilation recovery of the deep Southern Ocean, and by extension, to the deglacial CO 2 rise.

  the sediment delivery to the southwest Atlantic is currently dominated by loess, and by the Parana River sediments. A large proportion of the African continent comprises Archean Cratons (western Africa, Congo), and rocks related to the Pan African Orogen. The cratons are composed of gneisses while the Pan African Orogen is mainly composed of flysch deposits associated with volcanic formations, and intruded by granitoids. The overall geochemical composition of Africa is intermediate to very unradiogenic Nd, and intermediate to very radiogenic Sr and Pb

  (a) and (b) Variation of the coarse Figure 2: and fine grain size mode values, respectively, through time. Black lines represent the average value for both grain-size modes while dashed lines represent their standard deviation; (b) typical grain-size distribution curve from the core MD07-3076Q. Two grain-size modes can be identified from the grain-size distribution curve. YD: Younger Dryas, BA: Bølling Allerød, HS: Heinrich Stadial; LGM: Last Glacial Maxima.

  .a), and decreases during the deglaciation and reaches its minimum values after the Younger Dryas (YD). The average size of the fine mode (hereafter mentioned as the cohesive silt mode) is maximum at the end of the LGM and displays its lowest values during the deglaciation (figure 2.b). Clay mineral data from core MD07-3076Q. Purple dots represent the Figure 3: radiocarbon dates used for the age model. (a) relative proportion of smectite (%); (b) smectite crystallinity (°2θ); (c) illite crystallinity (°2θ); (b) and (c) note that the lower is the crystallinity index, the better the mineral is crystallized; (d) relative proportion of illite (%); (e) relative proportion of chlorite (%); (f) relative proportion of kaolinite; (g) kaolinite/chlorite ratio (K/C); (h) illite/smectite ratio (I/S).

  .a), illite ((I) 21-40%; figure 3.d), chlorite ((C) 12-33%; figure 3.e), and kaolinite ((K) 5-14%; figure 3.f) with higher smectite content at the end of the deglaciation, and higher illite, chlorite and kaolinite contents during the LGM. The smectite crystallinity ranges from 0.89 and 1.45 (figure 3.b) and varies in phase with the smectite content with slightly higher variability between 25 and 30 ka. The illite crystallinity varies between 0.27 and 0.42 (figure 3.c and 4) without major variation. Clay mineral proportions are relatively stable during the LGM but records a shift during the deglaciation with an increase of smectite compared to the other clay minerals. The smectite crystallinity varies simultaneously with smectite proportion changes.

5 ε

 5 Nd ), decreases by 2 ε units during the deglaciation and shows minimum values at the end of the deglaciation (figure5.c). The 87 Sr/ 86 Sr ratio ranges from 0.711 to 0.712: it is rather high and stable (<± 0.0003), during the last glaciation and displays a rapid decrease at ~15 ka. The ratio records a short rebound at 12.7 ka before reaching its minimum values at the end of the deglaciation (0.7107; figure 5.d). The 87 Sr/ 86 Sr ratio and the ε Nd show a similar temporal evolution (they both decrease during the deglaciation), which is surprising as in nature they usually record opposite relationship. The three Pb isotope ratios record their lowest values around 25 ka, and increase thereafter. This trend is more pronounced for the 207 Pb/ 204 Pb ratio during the deglaciation. Some fluctuations of the three ratios are observed during the deglaciation with higher ratios at climatic transitions (LGM/Heinrich Stadial 1 -HS1-, HS1/Bølling-Allerød -B-A -, B-A/Younger Dryas -YD-, Holocene onset), and low values during the middle of the HS1, the middle of the B-A, and the second half of the YD (except for the 206 Pb/ 204 Pb).

Figure 5 :

 5 fraction (20-32/40 µm); (b) ε Nd from the cohesive silt mode fraction (2-20 µm); (c) ε Nd from the clay-size fraction (<2 µm); (d) 87 Sr/ 86 Sr from the clay-size fraction (<2 µm); (f) 87 Sr/ 86 Sr from the sortable silt mode fraction (20-32/40 µm); (g) 87 Sr/ 86 Sr from the cohesive silt mode fraction (2-20 µm); (h) 208 Pb/ 204 Pb, (i) 207 Pb/ 204 Pb, and (j) 206 Pb/ 204 Pb from the clay-size fraction (<2 µm).

  types of sources:[START_REF] Skinner | Radiocarbon evidence for alternating northern and southern sources of ventilation of the deep Atlantic carbon pool during the last deglaciation[END_REF] Patagonia and Antarctic Peninsula with a crystallinity of1.5; and (2) smectite record very similar variations that suggest a dominant and rather continuous flux of smectite from the Scotia Arc (low crystallinity -~1.1) during the last glacial period, with a supplementary supply of less well crystallized smectite (slightly higher crystallinity -1.5; ~20%) from Patagonia or Antarctic Peninsula during the deglaciation (supplementary figures S1 and S2)In summary, both the proportions of the clay minerals and their crystallographic properties suggest that kaolinite mainly derives from low latitude areas, chlorite originates from Antarctica and the Scotia Sea, while illite mainly derives from the Weddell Sea embayment and smectite is derived from several sources (Scotia Arc, Patagonia, and Antarctic Peninsula). Moreover, mineralogical and crystallographic properties exclude Africa as a source of clay minerals consistent with the dominant westward oceanic circulation in the ACC (figure1). 87 Sr/ 86 Sr-ε Nd diagram of MD07-3076Q sediments and of potential sources of Figure 6: sediments for the South Atlantic Basin. Boxes representing the reference data delimit the first and the third quartile. The median values are represented by horizontal and vertical lines attached to the boxes for the ε Nd and the 87 Sr/ 86 Sr ratios, respectively. The short strokes at the end of these lines represent the 10 th and 90 th percentile values. Accordingly, the box represent 50% of values found for each potential provenance, and 80% is represented with the lines.

  Figure 7:sediments. The reference data used for comparison are from[START_REF] Fretzdorff | Petrogenesis of the back-arc east scotia ridge, south Atlantic ocean[END_REF], -Scotia Ridge-;Khondoker et al. (

Scotia

  Arc or southern Patagonia in the Argentine Basin. The main clay minerals in the Weddell Sea embayment are illite associated with chlorite. Smectite may be injected in the AABW at the vicinity of the Scotia Arc. Kaolinite is almost absent in both the Weddell Sea embayment and the Scotia Sea area (Patagonia, Antarctic Peninsula and Scotia Arc) and is unlikely to be transported by the AABW. The isotopic composition of fine particles transported by the AABW ranges between two end-members: the very old sediments from East Antarctica ( 87 Sr/ 86 Sr > 0.72; ε Nd < -20), and younger material from the Antarctic Peninsula and the Scotia Arc ( 87 Sr/ 86 Sr ~ 0.70; ε Nd > -5; intermediate Pb isotope ratios).

  The illite/smectite and kaolinite/smectite ratios have been plotted in figure8. The three end-members for AABW, CDW and NADW are plotted according to the clay composition of their suspended loads. Figure8highlights how the relative contribution of the three water masses (i.e., AABW, CDW, and NADW) to clay deposition has changed with time since the LGM. To interpret this figure it is important to keep in mind that changes observed in the contribution one deep water mass are relative compared to the other water masses. To construct figure 8.b, the proportion of clay particles deposited by each deep water mass was calculated as described below. End-member deep water mass compositions were calculated from the average composition of deep water-masses shown in figure 8.a. Weights are computed as the inverse of the distance between the position of water-mass end-member (x w ;y w ) with x w =K/C w and y w =I/S w and the position of the data point (x d ;y d ), with x d =K/C d and y d =I/S d taken from the graph (figure 8.a) for each water-mass: W w =1/[ (x d -xw) 2 +(y d -y w ) 2 ] 1/2 . The position used for the deep water masses are: xA ABW = K/C AABW = 0.3 ; y AABW = I/S AABW = 2.5 ; x CDW = K/C CDW = 0.1 ; y CDW = I/S CDW = 1 ; x NADW = K/C NADW = 0.9 ; y NADW = I/S NADW = 1. The values used for the NADW correspond to the mineralogical composition of the NADW during the LGM.

  ; (h) proportion of clay particles delivered by the NADW (see figure 8.b); (i) proportion of clay particles delivered by the CDW (see figure 8.b); (j) proportion of clay particles delivered by the AABW (see figure 8.

  LCDW speed slightly decreased, but remained high. Since ~15 ka, the LCDW speed has been showing a gradual decrease. McCave et al. (2014) observed minor change in the Antarctic Circumpolar Current (which includes the CDW) flow speed at the Drake Passage during the deglaciation. Our observation, however, is consistent with other studies in the south Indian sector of the Southern Ocean indicating that the Antarctic Circumpolar Current (which includes the CDW) flow speed was maximum during the LGM and decreased during the deglaciation

  the AABW. At ~16 ka, a slowdown of the AABW is indicated by a second sharp decrease of the cohesive silt mode (figure2), which reaches its lowest values of the entire record, indicating low AABW speed from 16 to 11.5 ka, when the AABW activity increased suddenly and recovered the speed observed before 16 ka.These variations of the AABW speed could indicate the transition from the Ice ShelfMode dominated bottom water formation at the end of the LGM to the Polynyas Mode dominated bottom water formation during interglacial periods. The variations of the cohesive silt mode support a strong AABW during the LGM and the early Holocene, and a minimum flow during the deglaciation. This minimum flow would result from the reduction of bottom water production via the Ice Shelf Mode and still low production via the Polynyas Mode. Our results confirm the results of[START_REF] Krueger | North Atlantic Deep Water and Antarctic Bottom Water variability during the last 200ka recorded in an abyssal sediment core off South Africa[END_REF] who demonstrated the relation between the flow speed changes in the Cape Basin and the higher AABW production rates and indicate that the size of the cohesive silt mode is a reliable tracer of the AABW flow speed and hence of AABW production rates in the Weddell Sea.

  addition, poorly ventilated deep Southern Ocean associated with a vigorous deep circulation (i.e., high AABW and LCDW flow) suggests that a barrier existed between the deep ocean and the surface, which is consistent with the study of[START_REF] Howe | North Atlantic Deep Water Production during the Last Glacial Maximum[END_REF]. In contrast, direct comparison highlights the fact that the peaks of ventilation age and of the AABW flow are not in phase. Indeed, the peaks of the AABW flow (figure 9.b) and of the AABW contribution to clay deposition (figure 9.j) are synchronous with the first decrease in deep water ventilation ages after the LGM and prior to HS1. Moreover, this well-defined change in the AABW behavior is recorded by two distinct proxies (i.e., clay minerals and grain size distribution) and in two distinct grain size fractions (clays and silts). These synchronous changes are associated with a drop in ventilation age prior to the HS 1. The variations in two grain size fractions that are transported and deposited by distinct dynamic processes indicates a major perturbation in Southern Ocean circulation. Interestingly, the increase in the AABW strength associated to the early decrease in deep water ventilation age took place significantly earlier than the changes recorded by the other proxies measured in core MD07-3076Q (i.e., sea water

  [START_REF] Skinner | Radiocarbon evidence for alternating northern and southern sources of ventilation of the deep Atlantic carbon pool during the last deglaciation[END_REF] vigorous LCDW during the LGM and a marked weakening from ~15 ka; (2) strong AABW at the end of the LGM and during the early Holocene, and weak AABW during the deglaciation between 16 and 11.5 ka. These results suggest a decrease of AABW production rates during the deglaciation that could result from the transition from strong Ice Shelf Mode bottom water production during the LGM to stronger Polynyas Mode bottom water during the Holocene.The strong LCDW speed observed during the LGM is associated with increased clay deposition by the CDW, and the reduction of LCDW speed since the B/A is accompanied by an increased clay contribution from the NADW. Similarly, the highest AABW speed recorded at the end of the LGM is concomitant with the highest relative contribution of the AABW to clay mineral deposition. Interestingly, this AABW maximum preceded the HS 1 and both its speed and contribution fell markedly at the LGM/HS 1 transition.

TABLE 1 :

 1 Average values of the different proxies for the entire record, the LGM, and the deglaciation.

Acknowledgments

We wish to thank Richard Smeets for his invaluable help in the clean lab, Emmeke Bos, Janne Koorneef, and Mathijs van de Ven for the help with TIMS Triton measurements, Bas van der Wagt and Kirsten van Zuilen for Neptune MC-ICPMS measurements. Tristan Lippens is thanked for computer support. We also wish to thank all organizations that provided financial support to the project: the "region Haut de France" and the Vrije Universiteit of Amsterdam. The research was supported by Europlanet 2020 RI, which received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 654208. We also want to express our special thanks to the "flotte océanographique française" for retrieving the sediment core used in this study. FB and VBR thanks Monique Gentric for administrative support. CW acknowledges support from the European Research Council ERC grant ACCLIMATE/n° 339108. and Planetary Science Letters 317-318, 374-385.