Eleonora Regattieri

Biagio Giaccio

Giorgio Mannella

Giovanni Zanchetta

Sebastien Nomade

Andrea Tognarelli

Natale Perchiazzi

Hendrik Vogel

Chiara Boschi

Russell Neil Drysdale

; B Giaccio

; G Mannella

; G Zanchetta

; S Nomade

; A Tognarelli

; H Vogel

; C Boschi

; R N Drysdale

; B Wagner

; M Gemelli

; P C Tzedakis

Frequency and dynamics of millennial-scale variability during Marine Isotope Stage 19: Insights from the Sulmona Basin (central Italy)

Keywords: Stable isotope geochemistry, interglacial variability, central Italy, lacustrine succession, MIS 19

établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The recovery of high-resolution records of climate variability from oceans, ice-sheets and continental archives has profoundly modified our perspective on global climate change by revealing the pervasive existence of very rapid and high-amplitude climate changes in the past (e.g. [START_REF] Gottschalk | Abrupt changes in the southern extent of North Atlantic Deep Water during Dansgaard-Oeschger events[END_REF].

Although such abrupt climatic changes can be triggered by different forcing, it is conceivable that human activity has likely increased their probability (Alley et al., 2003). Thus, the recognition of short-term (i.e. multi-decadal to sub-millennial), global-scale, climate variability during previous interglacial periods is of fundamental importance to provide the context of natural variability in which human-induced changes operate [START_REF] Tzedakis | Interglacial diversity[END_REF].

Among older interglacial periods, Marine Isotope Stage (MIS) 19c has received particular attention due to its orbital geometry, which was very similar to that of the present interglacial (i.e., low eccentricity and weak precession, and similar phasing between precession and obliquity: [START_REF] Berger | Insolation values for the climate of the last 10 million years[END_REF][START_REF] Pol | New MIS 19 EPICA Dome C high-resolution deuterium data: hints for a problematic preservation of climate variability in the "oldest ice[END_REF][START_REF] Tzedakis | The MIS 11 -MIS 1 analogy, southern European vegetation, atmospheric methane and the "early anthropogenic hypothesis[END_REF][START_REF] Tzedakis | Determining the natural length of the current interglacial[END_REF]. Modelling studies have highlighted that this period is the best analogue for the Holocene when annual and seasonal temperatures are taken into account, although it appears less similar when the summer-half yearly insolation is considered (Yin andBerger 2010, 2012). Because MIS 19c occurred before the Mid-Brunhes Event (~450 ka) -i.e. before the culmination of a series of changes of the global climate system resulting in the establishment of longer and deeper glacial-interglacial cycles (e.g. [START_REF] Head | The Early-Middle Pleistocene transition: characterization and proposed guide for the defining boundary[END_REF] -it was also characterized by slightly lower global temperatures and atmospheric CO2 concentrations with respect to the preindustrial Holocene, and possibly by higher residual global ice-volume [START_REF] Bintanja | Modelled atmospheric temperatures and global sea levels over the past million years[END_REF][START_REF] Bintanja | North American ice-sheet dynamics and the onset of 100,000year glacial cycles[END_REF][START_REF] Lüthi | High-resolution carbon dioxide concentration record 650,000-800,000 years before present[END_REF][START_REF] Lisiecki | A Pliocene-Pleistocene stack of 57 globally distributed benthic δ 18 O records[END_REF][START_REF] Elderfield | Evolution of ocean temperature and ice volume through the mid-Pleistocene climate transition[END_REF]. Millennial-to centennial-scale climate oscillations during MIS 19, and particularly within substage MIS 19c, have been previously reported from both marine and continental archives [START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF]Maegakiuchi et al., 2017;Oliveira et al., 2018;[START_REF] Kleiven | Coupled deep-water flow and climate variability in the middle Pleistocene North Atlantic[END_REF][START_REF] Maiorano | Climate signatures through Marine Isotope Stage 19 in the Montalbano Jonico section (Southern Italy): A land-sea perspective[END_REF]Marino et al., 2015;[START_REF] Ferretti | The Marine Isotope Stage 19 in the mid-latitude North Atlantic Ocean: astronomical signature and intra-interglacial variability[END_REF][START_REF] Nomade | High-resolution foraminifer stable isotope record of MIS 19 at Montalbano Jonico, southern Italy: a window into Mediterranean climatic variability during a low-eccentricity interglacial[END_REF]. The findings of a ~5-kyr periodicity, i.e., similar to the fourth harmonic of precession, in both the coupled marine-pollen record from the southern Iberian margin (site U1385, [START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF] and in the planktonic and benthic δ 18 O record from low to mid-latitude North Atlantic and Mediterranean records [START_REF] Ferretti | The Marine Isotope Stage 19 in the mid-latitude North Atlantic Ocean: astronomical signature and intra-interglacial variability[END_REF][START_REF] Weirauch | Evolution of millennial-scale climate variability during the mid-Pleistocene[END_REF][START_REF] Nomade | High-resolution foraminifer stable isotope record of MIS 19 at Montalbano Jonico, southern Italy: a window into Mediterranean climatic variability during a low-eccentricity interglacial[END_REF] led to the suggestion that variations in the tropical seasonal insolation cycle, driven by precession and its harmonics, caused periodic oscillations in the latitudinal thermal gradient. These oscillations were considered capable of altering both sea-surface conditions and westerly wind trajectories, modifying the northward transport of heat and water vapour [START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF]. Further north, however, the record of outflow speed from the Nordic Sea and the isotopic composition of surface and bottom waters from site ODP-983 (Fig. 1, [START_REF] Kleiven | Atlantic Ocean thermohaline circulation changes on orbital to suborbital timescales during the mid-Pleistocene[END_REF][START_REF] Kleiven | Coupled deep-water flow and climate variability in the middle Pleistocene North Atlantic[END_REF], located near the eastern source of North Atlantic Deep Water (NADW), shows a series of millennial-scale episodes of reduced ventilation of intermediate waters and reduction in deep convection strength during the whole MIS 19 period. These oscillations have been related to changes in local convection and to reduced NADW formation, leading to intervals of weakened Atlantic Meridional Overturning Circulation (AMOC) [START_REF] Kleiven | Coupled deep-water flow and climate variability in the middle Pleistocene North Atlantic[END_REF]. As AMOC disruptions affect also Mediterranean climate, causing decreases in temperature and precipitation (e.g. [START_REF] Columbu | Early last glacial intra-interstadial climate variability recorded in a Sardinian speleothem[END_REF][START_REF] Drysdale | Stalagmite evidence for the precise timing of North Atlantic cold events during the early last glacial[END_REF][START_REF] Fletcher | A centennial-scale record of vegetation and climate variability from 312 to 240 ka (Marine Isotope Stages 9c-a, 8 and 7e) from Tenaghi Philippon, NE Greece[END_REF][START_REF] Margari | Character of vegetational and environmental changes in southern Europe during the last glacial period; evidence from Lesvos Island, Greece[END_REF][START_REF] Regattieri | Hydrological variability over the Apennines during the Early Last Glacial precession minimum, as revealed by a stable isotope record from Sulmona Basin, Central Italy[END_REF][START_REF] Regattieri | A multi-proxy record of MIS 11-12 deglaciation and glacial MIS 12 instability from the Sulmona Basin (central Italy)[END_REF][START_REF] Regattieri | A MIS 9/MIS 8 speleothem record of hydrological variability from Macedonia (FYROM)[END_REF][START_REF] Tzedakis | Enhanced climate instability in the North Atlantic and southern Europe during the Last Interglacial[END_REF], the ODP-983 record points to high-latitude forcing of the observed variability. These contrasting findings thus leave open questions about oceanic and atmospheric mechanisms operating at sub-millennial scales during MIS 19 and, particularly, in its interglacial portion, and it is not clear if and how these processes can be linked to boundary conditions. Part of this uncertainty is also due to the lack of robust and independent chronologies, an issue which until now has clearly hampered our capability to asses the timing, rate, propagation and duration of changes.

Here we present a multiproxy biogeochemical record (high resolution stable oxygen and carbon isotope on lacustrine calcite, low-resolution elemental and mineralogical composition on the bulk sediment, biogenic silica content) from a stratigraphic interval containing the MIS 19c, which is part of the lacustrine succession hosted in the Sulmona Basin (central Italy, Fig. 1). Sediment proxies from Sulmona Basin record local environmental conditions, which can be linked to North Atlantic climate variability [START_REF] Giaccio | Duration and dynamics of the best orbital analogue to the present interglacial[END_REF][START_REF] Regattieri | Hydrological variability over the Apennines during the Early Last Glacial precession minimum, as revealed by a stable isotope record from Sulmona Basin, Central Italy[END_REF][START_REF] Regattieri | A multi-proxy record of MIS 11-12 deglaciation and glacial MIS 12 instability from the Sulmona Basin (central Italy)[END_REF][START_REF] Regattieri | A Last Interglacial record of environmental changes from the Sulmona Basin (central Italy)[END_REF]. An important feature of the Sulmona succession is the presence of numerous volcanic ash (tephra) layers interbedded within the lacustrine sediment (e.g. [START_REF] Giaccio | The late MIS 5 Mediterranean tephra markers: a reappraisal from peninsular Italy terrestrial records[END_REF][START_REF] Giaccio | Tephra layers from Holocene lake sediments of the Sulmona Basin, central Italy: implications for volcanic activity in Peninsular Italy and tephrostratigraphy in the central Mediterranean area[END_REF]. 40 Ar/ 39 Ar dating performed directly on those tephra layers provides robust and independent chronological constraints for the observed variability. [START_REF] Giaccio | Duration and dynamics of the best orbital analogue to the present interglacial[END_REF] presented the entire MIS 20 to MIS 17 interval from Sulmona, providing a relatively low-resolution stable isotope record for the 820-720 ka period and with a particular focus on the length of the MIS 19c interglacial.

Here, this interglacial is investigated at higher resolution (sub-centennial) using a multi-proxy approach, and the record is anchored to an improved chronology. We explore the environmental expression, the pacing and the periodicities of the centennial-to millennial-scale variability revealed by the Sulmona record. We then compare this to marine records from the mid-and high-latitudes of the North Atlantic, to unravel the potential forcing and the mechanisms for short-term instability within MIS 19c at the extraregional scale.

Site setting and stratigraphy

The Sulmona Basin (Fig. 1) is a block-faulted intermountain depression located in the central Apennine Ridge (central Italy). The basin experienced discontinuous lacustrine sediment accumulation during the Quaternary [START_REF] Boretto | Stratigraphy, pedological features, paleontology, geochemistry and chronology of the "loess-like" deposits of the Buca dei Corvi Section (central Italy)[END_REF][START_REF] Giaccio | The late MIS 5 Mediterranean tephra markers: a reappraisal from peninsular Italy terrestrial records[END_REF][START_REF] Giaccio | Revised chronology of the Sulmona lacustrine succession, central Italy[END_REF]. Its location and the geological, stratigraphic and chronological framework were described in detail in previous studies [START_REF] Giaccio | Tephra layers from Holocene lake sediments of the Sulmona Basin, central Italy: implications for volcanic activity in Peninsular Italy and tephrostratigraphy in the central Mediterranean area[END_REF][START_REF] Giaccio | The late MIS 5 Mediterranean tephra markers: a reappraisal from peninsular Italy terrestrial records[END_REF][START_REF] Giaccio | Revised chronology of the Sulmona lacustrine succession, central Italy[END_REF][START_REF] Regattieri | Hydrological variability over the Apennines during the Early Last Glacial precession minimum, as revealed by a stable isotope record from Sulmona Basin, Central Italy[END_REF][START_REF] Regattieri | A multi-proxy record of MIS 11-12 deglaciation and glacial MIS 12 instability from the Sulmona Basin (central Italy)[END_REF][START_REF] Regattieri | A Last Interglacial record of environmental changes from the Sulmona Basin (central Italy)[END_REF][START_REF] Zanchetta | Middle Pleistocene (MIS 14) environmental conditions in the central Mediterranean derived from terrestrial molluscs and carbonate stable isotopes from Sulmona Basin (Italy)[END_REF]. Briefly, the Sulmona sedimentary succession is divided into three main unconformity-bounded lithostratigraphic units (SUL6, SUL5 and SUL4-3), composed of alluvial, fluvial and lacustrine sediments. These units were chronologically constrained by magnetostratigraphy and tephrochronology [START_REF] Giaccio | The late MIS 5 Mediterranean tephra markers: a reappraisal from peninsular Italy terrestrial records[END_REF][START_REF] Giaccio | Revised chronology of the Sulmona lacustrine succession, central Italy[END_REF][START_REF] Giaccio | Duration and dynamics of the best orbital analogue to the present interglacial[END_REF][START_REF] Sagnotti | Extremely rapid directional change during Matuyama-Brunhes geomagnetic polarity reversal[END_REF][START_REF] Sagnotti | How fast was the Matuyama-Brunhes geomagnetic reversal? A new subcentennial record from the Sulmona Basin, central Italy[END_REF]. This study focuses on the outcropping 35-43 m depth interval of the SUL6 lacustrine unit (Fig. 1). The SUL6 unit spans the period between MIS 20 and MIS 16 (820-650 ka) and encompasses the Matuyama-Brunhes geomagnetic reversal [START_REF] Sagnotti | Extremely rapid directional change during Matuyama-Brunhes geomagnetic polarity reversal[END_REF][START_REF] Mark | High-precision 40Ar/39Ar dating of Pleistocene tuffs and temporal anchoring of the Matuyama-Brunhes boundary[END_REF]. The SUL6 succession has been described by [START_REF] Giaccio | Tephra layers from Holocene lake sediments of the Sulmona Basin, central Italy: implications for volcanic activity in Peninsular Italy and tephrostratigraphy in the central Mediterranean area[END_REF], with important chronological amendments in [START_REF] Giaccio | Revised chronology of the Sulmona lacustrine succession, central Italy[END_REF]. Sediments are composed of light-coloured lacustrine calcareous marls [START_REF] Freytet | Lacustrine and palustrine carbonate petrography: an overview[END_REF], with up to 90% wt CaCO3 and abundant diatom remains (SOM-Fig. S1). The carbonate fraction is almost entirely made up of euhedral to sub-euhedral calcite crystals of ~3-5 μm (SOM-Fig. S1), typical of biologically-mediated inorganic carbonate precipitation from Ca 2+ and HCO3 -ions dissolved in surface water. Hereafter we refer to it as endogenic calcite (e.g. [START_REF] Jones | The mineralogy and related chemistry of lake sediments[END_REF]. The contribution of clastic carbonates from the catchment is negligible and thus has no effect on the stable isotope (δ 18 O and δ 13 C) composition of calcite [START_REF] Regattieri | A multi-proxy record of MIS 11-12 deglaciation and glacial MIS 12 instability from the Sulmona Basin (central Italy)[END_REF][START_REF] Regattieri | A Last Interglacial record of environmental changes from the Sulmona Basin (central Italy)[END_REF]. Several tephra layers occur within the SUL6 unit (Fig. 1) and form the basis of its chronology.

The topographic surface of the Sulmona basin is located between 340 and 400 m a.s.l., but its hydrology is dominated by a network of karst springs fed by recharge occurring in the surrounding mountain areas (up to 2500 m a.s.l.) [START_REF] Barbieri | Stable isotope ( 2 H, 18 O and 87 Sr/ 86 Sr) and hydrochemistry monitoring for ground water hydrodynamics analyses in a karst aquifer (Gran Sasso, Central Italy)[END_REF]Desiderio et al., 2005aDesiderio et al., , 2005b;;[START_REF] Falcone | Chemical and isotopic (δ 18 O‰, δ 2 H‰, δ 13 C‰, 222 Rn) multi-tracing for groundwater conceptual model of carbonate aquifer (Gran Sasso INFN underground laboratory-central Italy)[END_REF]. Spring waters are characterized by a pH close to 7.5, an electrical conductivity of <500 μS and a high discharge (e.g. average 7 m 3 s -1 for the main spring, Capo Pescara), especially during snow melt in spring [START_REF] Barbieri | Stable isotope ( 2 H, 18 O and 87 Sr/ 86 Sr) and hydrochemistry monitoring for ground water hydrodynamics analyses in a karst aquifer (Gran Sasso, Central Italy)[END_REF] and likely accounted for most of the paleolake recharge [START_REF] Regattieri | Hydrological variability over the Apennines during the Early Last Glacial precession minimum, as revealed by a stable isotope record from Sulmona Basin, Central Italy[END_REF][START_REF] Regattieri | A multi-proxy record of MIS 11-12 deglaciation and glacial MIS 12 instability from the Sulmona Basin (central Italy)[END_REF][START_REF] Regattieri | A Last Interglacial record of environmental changes from the Sulmona Basin (central Italy)[END_REF].

Owing to the intense neotectonic activity, which has reshaped the local hydrography, the hydrological regime of Sulmona paleolake cannot be defined. However, based on the modern hydrography and hydrogeochemistry of the basin, as well as the observation that sediments are almost entirely composed of massive beds of endogenic calcite containing abundant and well-preserved diatom remains, it can be argued that it was a freshwater and hydrologically open basin. The stable isotope composition of the endogenic calcite is also consistent with this interpretation [START_REF] Regattieri | Hydrological variability over the Apennines during the Early Last Glacial precession minimum, as revealed by a stable isotope record from Sulmona Basin, Central Italy[END_REF][START_REF] Regattieri | A multi-proxy record of MIS 11-12 deglaciation and glacial MIS 12 instability from the Sulmona Basin (central Italy)[END_REF][START_REF] Regattieri | A Last Interglacial record of environmental changes from the Sulmona Basin (central Italy)[END_REF].

Local precipitation averages ~700 mm/yr but increases up to 1200 mm/yr at high altitude. Rainfall is unevenly distributed, showing maxima during autumn and winter, and minima during the summer season. Winter precipitation is mostly related to north-westerly circulation. Cyclones originate over the North Atlantic and take a mid-latitude storm track, following a prevailing NW-SE direction [START_REF] Reale | Synoptic climatology of winter intense precipitation events along the Mediterranean coasts[END_REF]. Secondary cyclones, often associated with the passage of major cyclones north of the Mediterranean, form within the basin and especially in the Gulf of Genoa, the most important Mediterranean cyclogenetic centre (Lionello et al., 2006). The amount of winter precipitation reaching the Mediterranean is influenced by several large-scale atmospheric patterns, which induce changes in storm-track activity. In particular, at multiannual and decadal scales, the amount of winter precipitation is inversely correlated with the North Atlantic Oscillation (NAO) index (e.g. Lopez-Moreno et al., 2011;[START_REF] Ulbrich | Climate of the Mediterranean: synoptic patterns, temperature, precipitation, winds, and their extremes[END_REF][START_REF] Cullen | Impact of the North Atlantic Oscillation on Middle Eastern climate and streamflow[END_REF], because during negative NAO phases westerly storm tracks are shifted southward and allow a greater penetration of storms into the basin, and because negative NAO phases enhance Mediterranean cyclogenesis [START_REF] Ulbrich | Climate of the Mediterranean: synoptic patterns, temperature, precipitation, winds, and their extremes[END_REF]. Summer droughts are due to the expansion of the Azores high [START_REF] Xoplaki | Mediterranean summer air temperature variability and its connection to the large-scale atmospheric circulation and SSTs[END_REF]Ulbrich et al., 2012 and references therein). Summer precipitation is scarce and mostly related to local heat lows, which owe their genesis to thermal heating overland, and to evaporation and convection influenced by the surrounding mountain topography.

Methods

Sampling and stable isotope analyses

The studied interval comprises three distinct outcropping and partially overlapping sections that are lithostratigraphically correlated through clearly distinguishable tephra horizons (Fig. 1). The composite section is eight metres thick and was sampled for stable isotope analyses at 2.5 cm vertical resolution, for a total of ~320 samples. Sample preparation followed the procedure described in [START_REF] Regattieri | Hydrological variability over the Apennines during the Early Last Glacial precession minimum, as revealed by a stable isotope record from Sulmona Basin, Central Italy[END_REF]. Stable isotope analyses were performed at the Stable Isotope Laboratory of the Institute of Geosciences and Earth Resources of the Italian National Research Council (IGG-CNR, Pisa, Italy) with a Gas Bench II (Thermo Scientific) coupled to a Delta XP IRMS (Finnigan), following the method presented in [START_REF] Regattieri | A multi-proxy record of MIS 11-12 deglaciation and glacial MIS 12 instability from the Sulmona Basin (central Italy)[END_REF]. Sample results are reported on the VPDB scale and calibrated against the international standards NBS-18 and NBS-19. Analytical uncertainties were 0.17‰ and 0.15‰ for δ 18 O and δ 13 C respectively (2σ).

Elemental, mineralogical and biogenic silica analyses

X-ray fluorescence spectrometry (XRF) and X-ray powder diffraction (XRPD) analyses were performed on untreated leftover powders of the stable isotope analyses at the Earth Sciences Department of the University of Pisa (Italy). Elemental analyses were conducted with a NITON XL3t GOLDD + hand-held XRF unit (HHXRF, see [START_REF] Gemelli | Chemical analysis of iron meteorites using a hand-held Xray fluorescence spectrometer[END_REF] for performance), following the analytical procedure for sediment samples described in [START_REF] Regattieri | A multi-proxy record of MIS 11-12 deglaciation and glacial MIS 12 instability from the Sulmona Basin (central Italy)[END_REF].

Mineralogical composition was investigated on 36 unevenly spaced samples through XRPD analyses with a Bruker D2 Phaser diffractometer equipped with a Lynxeye fast detector. Phase identification was obtained with the Bruker Diffrac-Suite EVA and Topas-Academic software [START_REF] Coelho | TOPAS and TOPAS-Academic: an optimization program integrating computer algebra and crystallographic objects written in C++[END_REF]. A semiquantitative estimation of mineral abundances (quartz/calcite ratio, qz/ct hereafter), was calculated with the abovementioned software as the ratio between spectral peak areas of quartz and calcite. Biogenic silica (bSi) concentrations were measured on the same samples analysed with XRF, using Fourier transform infrared spectroscopy (FTIRS) at the Institute of Geological Sciences, University of Bern, Switzerland. Analyses were performed using the method described in [START_REF] Vogel | Fourier transform infrared spectroscopy, a new cost-effective tool for quantitative analysis of biogeochemical properties in long sediment records[END_REF] and adopting the sample preparation protocol of [START_REF] Vogel | Quantification of biogenic silica by means of Fourier transform infrared spectroscopy (FTIRS) in marine sediments[END_REF]. Calibration, accuracy and precision are detailed in [START_REF] Meyer-Jacob | Independent measurement of biogenic silica in sediments by FTIR spectroscopy and PLS regression[END_REF].

Ar/Ar dating and age modelling

The Bayesian age model (Fig. 2) is based on 40 Ar/ 39 Ar dating of six tephra layers (Fig. 1 and Table 1).

Four of these tephra layers occur within the interval analysed in this study (35-43 m depth, Fig. 1), while the remaining two occur in close proximity (at 46.14 m and 29.70 m) and were employed to better constrain the age-modelling procedure. For five of the six tephra, ages are from [START_REF] Giaccio | Duration and dynamics of the best orbital analogue to the present interglacial[END_REF], here recalculated using the new Optimisation Model age for the ACs monitor standard (1.891 Ma; [START_REF] Niespolo | Intercalibration and age of the Alder Creek sanidine 40 Ar/ 39 Ar standard[END_REF]. A new 40 Ar/ 39 Ar dating for the SUL2-19 tephra, obtained at the CNRS-LSCE (Centre National de la Recherche Scientifique, Laboratoire des Sciences du Climat et de l'Environnement, Gif Sur Yvette, France), is presented here (Fig. 2). Analytical procedures are as described in [START_REF] Giaccio | Duration and dynamics of the best orbital analogue to the present interglacial[END_REF]. Details concerning the analytical procedure and the full dataset are both given in supplementary material (SOM text 1 and SOM Table 1). This new age is calibrated against the ACs-2 age of 1.1891 (i.e. FCs at 28.294 Ma; [START_REF] Niespolo | Intercalibration and age of the Alder Creek sanidine 40 Ar/ 39 Ar standard[END_REF] and calculated using the total K decay constant of [START_REF] Renne | Joint determination of 40 K decay constants and 40Ar * /40K for the Fish Canyon sanidine standard, and improved accuracy for 40 Ar/ 39 Ar geochronology[END_REF]. The Bayesian age model (Fig. 2) was constructed using the Bacon software [START_REF] Blaauw | Flexible paleoclimate age-depth models using an autoregressive gamma process[END_REF]. "A priori" settings were chosen to accommodate the actual mean sedimentation rate (28.7 yr/cm), and to allow for larger variations around the mean value. Successive calculations with different settings held statistically indistinguishable age-depth relationships, although the current model minimizes the difference between radiometric and modelled tephra ages (Table 1).

Wavelet analyses

Continuous wavelet analyses (CWT) was performed on δ 18 O data series for the whole interval between 800 ka and 750 ka, including lower resolution data from [START_REF] Giaccio | Duration and dynamics of the best orbital analogue to the present interglacial[END_REF] for the periods not covered by the new record, employing a self-implemented Matlab code described in [START_REF] Tognarelli | The Use of Continuous Wavelet Transform for Ground-Roll Attenuation[END_REF] and in [START_REF] Tognarelli | The Use of Continuous Wavelet Transform for Ground-Roll Attenuation[END_REF]. No filtering was performed before the wavelet analysis in order to preserve the original frequency content of the input data. Only a linear interpolation is applied to the data to produce a regular sampling over time, and a Δt of 1 yr is used as sample rate. 95% significance levels in the wavelet power spectrum were computed by means of a chi-square test with two degrees of freedom, where the null hypothesis assumes the that the local wavelet power spectrum corresponds to the rednoise spectrum with a lag-1 coefficient of 0.73. Power bands for the most intense periodicities were extracted from the spectra through the inverse continuous wavelet transform.

Results and discussion

Chronology

Full analytical details for the 35 individual sanidine crystals of the SUL2-19 tephra are given in Table S1. Among the 35 analysed, 29 yielded ages overlapping within uncertainty, allowing the calculation of a weighted mean age of 784.7 ± 2.4 ka (2σ including J uncertainty) (Fig. 2 and Table 1).

According to the age model presented in Fig. 2, the new high-resolution δ 18 O record presented in this study spans the 769.8 ± 2.2 ka to 789.9 ± 2.1 ka period. The mean associated uncertainty of the record is 2.6 kyr, ranging from 2.1 to 2.8 kyr (Fig. 2). The resulting average temporal resolution of the stable isotope series is 60 years, while the temporal resolution of XRF and bSi analyses is 230 years. XRD samples are not evenly spaced, but on average their resolution is ~ 600 years. The sedimentation rate is on average 0.45 mm/yr, ranging from 0.18 mm/yr to 0.73 mm/yr.

Proxy interpretation

Different sediment properties presented in this work (δ 13 C, δ 18 O, Ca content, biogenic silica content mineralogical composition, Fig. 3) have been measured and discussed previously for other lacustrine intervals in Sulmona [START_REF] Giaccio | Duration and dynamics of the best orbital analogue to the present interglacial[END_REF][START_REF] Regattieri | Hydrological variability over the Apennines during the Early Last Glacial precession minimum, as revealed by a stable isotope record from Sulmona Basin, Central Italy[END_REF][START_REF] Regattieri | A multi-proxy record of MIS 11-12 deglaciation and glacial MIS 12 instability from the Sulmona Basin (central Italy)[END_REF][START_REF] Regattieri | A Last Interglacial record of environmental changes from the Sulmona Basin (central Italy)[END_REF], so their paleoclimatic interpretation is only briefly outlined here and the reader is referred to previous works for more detailed explanation.

Oxygen and carbon stable isotopes

The oxygen stable isotope composition (δ 18 O) of lacustrine, biologically-induced, endogenic calcite depends on temperature and oxygen isotopic composition of the lake surface water (e.g. [START_REF] Leng | Palaeoclimate interpretation of stable isotope data from lake sediment archives[END_REF]). In the Mediterranean region, the temperature effect during carbonate precipitation (ca.

-0.24‰/°C; Kim and O'Neil, 2007) is negligible, because it is counterbalanced by a gradient of ca. +0.3‰/°C observed between mean annual δ 18 O of meteoric precipitation and temperature [START_REF] Bard | Hydrological conditions in the western Mediterranean basin during the deposition of Sapropel 6 (~175 kyr)[END_REF]. The δ 18 O of lake water depends on the δ 18 O of precipitation and on the precipitation/evaporation (P/E) ratio (e.g. [START_REF] Leng | Palaeoclimate interpretation of stable isotope data from lake sediment archives[END_REF]. The δ 18 O of Mediterranean precipitation has a strong empirical relationship with the amount of rainfall (ca. -2‰/100 mm), with lower values related to increased precipitation and higher values related to reduced precipitation [START_REF] Bard | Hydrological conditions in the western Mediterranean basin during the deposition of Sapropel 6 (~175 kyr)[END_REF]. Previous studies on lacustrine carbonates from the Sulmona Basin have shown that the influence of lake water evaporation for the final calcite δ 18 O is negligible, likely due to the large and sustained karstic recharge, to presumable hydrologically open conditions and relatively short water residence times within the lake. Therefore, the δ 18 O composition of endogenic calcite at Sulmona can be used as a first-order proxy for precipitation amount in the high-altitude catchment of the karst recharge system [START_REF] Giaccio | Duration and dynamics of the best orbital analogue to the present interglacial[END_REF][START_REF] Regattieri | Hydrological variability over the Apennines during the Early Last Glacial precession minimum, as revealed by a stable isotope record from Sulmona Basin, Central Italy[END_REF][START_REF] Regattieri | A multi-proxy record of MIS 11-12 deglaciation and glacial MIS 12 instability from the Sulmona Basin (central Italy)[END_REF][START_REF] Regattieri | A Last Interglacial record of environmental changes from the Sulmona Basin (central Italy)[END_REF]. Changes in isotopic composition driven by changes in the source area of moisture always contribute to changes in the δ 18 O of precipitation, and thus of precipitated carbonates. However, these variations have proven to be significant especially during glacial/interglacial transitions (e.g. Marino et al., 2015), but can be considered negligible during interglacial periods such as the period discussed here [START_REF] Tzedakis | Enhanced climate instability in the North Atlantic and southern Europe during the Last Interglacial[END_REF].

The stable carbon isotope composition of lacustrine endogenic calcite derives from that of the dissolved inorganic carbon (DIC) of the lake water [START_REF] Whittington | Lateglacial and early Holocene climates of the Atlantic margins of Europe: Stable isotope, mollusc and pollen records from Orkney, Scotland[END_REF][START_REF] Zanchetta | Multiproxy record for the last 4500 years from Lake Shkodra (Albania/Montenegro)[END_REF][START_REF] Zanchetta | Evidence for carbon cycling in a large freshwater lake in the Balkans over the last 0.5 million years using the isotopic composition of bulk organic matter[END_REF]). The DIC of the Sulmona paleolake was likely significantly influenced by the input of the large karst springs recharging the basin, which today show higher δ 13 CDIC (δ 13 CDIC(karst)) compared to smaller and more surficial springs, due to the longer rock-water interaction times [START_REF] Falcone | Chemical and isotopic (δ 18 O‰, δ 2 H‰, δ 13 C‰, 222 Rn) multi-tracing for groundwater conceptual model of carbonate aquifer (Gran Sasso INFN underground laboratory-central Italy)[END_REF]. Variations in δ 13 CDIC(karst) are related to rainfall and temperature fluctuations, with dry/cool periods characterized by reduced soil OM stocks and longer water residence times, leading to higher δ 13 CDIC(karst). Conversely, warmer and wetter conditions promote soil and vegetation development and a faster water flow, leading to more negative δ 13 CDIC(karst), as commonly inferred from speleothem studies (e.g. Genty et al., 2002;[START_REF] Regattieri | A continuous stable isotope record from the penultimate glacial maximum to the Last Interglacial (159-121 ka) from Tana Che Urla Cave (Apuan Alps, central Italy)[END_REF]. Within the lake, the δ 13 CDIC(karst) signal is mediated by additional processes, which involve equilibration with atmospheric CO2, photosynthetic 12 C uptake, and consumption and recycling of organic matter in the water column as well as in the sediment. These processes largely depend on the lake hydrological budget and settings (e.g. [START_REF] Leng | Palaeoclimate interpretation of stable isotope data from lake sediment archives[END_REF]. In our record, a generally weak covariance between δ 13 C and δ 18 O is observed, especially for the decreasing trend at the beginning of the record and for a similar interval of enriched values at ca. 772 ka (Fig. 3). On the whole, δ 13 C and δ 18 O also show a weak though significant statistical correlation (r=0.37, Fig. 4), though is visually clear that their relationship change during different intervals. A positive covariation of the two isotopes is usually observed in hydrologically closed lakes (e.g. [START_REF] Talbot | Paleolimnological Signatures from Carbon and Oxygen Isotopic Ratios in Carbonates, from Organic Carbon-Rich Lacustrine Sediments: Chapter 6. In Lacustrine Basin Exploration: Case Studies and Modern Analogs[END_REF]. In hydrologically open lakes, where calcite precipitation is mediated by primary productivity, an inverse relationship between δ 13 C and δ 18 O is instead expected (e.g. [START_REF] Talbot | Paleolimnological Signatures from Carbon and Oxygen Isotopic Ratios in Carbonates, from Organic Carbon-Rich Lacustrine Sediments: Chapter 6. In Lacustrine Basin Exploration: Case Studies and Modern Analogs[END_REF]. The current hydrology of the Sulmona Basin and the negligible effects of evaporation on the δ 18 O signal strongly suggest hydrologically open conditions for the Sulmona Lake, and relatively short water residence times within the lake. Thus, the weak covariance between δ 13 C and δ 18 O, rather than an indication of hydrological closure, likely indicates that the δ 13 CDIC(karst) signal is dominant on the final δ 13 C of calcite, and that the evolution of the δ 13 CDIC(karst) is modulated by climate conditions, mostly via the regulation of soil CO2 leached to the lake [START_REF] Zanchetta | Evidence for carbon cycling in a large freshwater lake in the Balkans over the last 0.5 million years using the isotopic composition of bulk organic matter[END_REF]. However, a divergence is apparent in the long-term trends of the two isotope time series, with progressively more negative δ 13 C values corresponding to increasing δ 18 O (Fig. 3). This decoupling could be related to the increasing influence of in-lake processes compared to that of karst recharge, which may possibly decrease. Alternatively, the trend towards more negative δ 13 C values can be explained by the slow post-glacial development of soils in the catchment, supplying more 13 C depleted CO2, following the progression of the interglacial, as already observed for speleothem records from high-altitude recharge areas [START_REF] Drysdale | Stalagmite evidence for the onset of the Last Interglacial in southern Europe at 129±1 ka[END_REF][START_REF] Regattieri | A continuous stable isotope record from the penultimate glacial maximum to the Last Interglacial (159-121 ka) from Tana Che Urla Cave (Apuan Alps, central Italy)[END_REF], Zanchetta et al., 2007).

Productivity and detrital proxies

In the Sulmona lacustrine sediment, Ca occurs mostly as endogenic calcite, as demonstrated by previous studies and by SEM microphotographs of the sediment (SOM, Fig. S1). Endogenic calcite precipitates through algal fixation of CO2, thus in this context Ca content is an indirect proxy for lake primary productivity. Biogenic silica (bSi) in the sediment primarily derives from diatom frustules and thus also provides information on primary productivity [START_REF] Vogel | A paleoclimatic record with tephrochronological age control for the last glacial-interglacial cycle from Lake Ohrid, Albania and Macedonia[END_REF]. Rising spring and summer temperatures and nutrient availability promote primary productivity. Calcite precipitation rate depends also on HCO3 -and Ca 2+ concentrations in the lake water, with enhanced ion supply through soil/epikarst dissolution processes and high soil CO2 production and leaching, both leading to higher dissolved ion content, during wetter and warmer periods (e.g. [START_REF] Francke | Sedimentological processes and environmental variability at Lake Ohrid (Macedonia, Albania) between 637 ka and the present[END_REF]. General agreement is observed between Ca and bSi content, but some differences are apparent (Fig. 3). At Sulmona, volcanic material from tephra deposition in the lake and mobilization of volcanoclastic deposits in the catchment was likely an important source for the Si and Fe needed for diatom growth. The single sample with high bSi content at ca. 789 ka occurs in close proximity (i.e. within 5 cm) of tephra T22. Tephra deposition following large eruptions can trigger short-term diatom blooms, which are not necessarily climate-related [START_REF] Cvetkoska | Quaternary climate change and Heinrich events in the southern Balkans: Lake Prespa diatompalaeolimnology from the last interglacial to present[END_REF][START_REF] D'addabbo | Ash leachates from some recent eruptions of Mount Etna (Italy) and Popocatépetl (Mexico) volcanoes and their impact on amphibian living freshwater organisms[END_REF]. It is also interesting that the main rise in bSi seems to lag the increase in Ca (Fig. 3). This difference could be potentially related to post-depositional dissolution of calcite. However, the sediment lithology does not show any evidence of anoxic, low pH conditions in the respective horizons (i.e. no laminations are present and the sediments are always massive, indicating continuing bioturbation and thus oxygenated conditions at the lake bottom), which would support such dissolution. Another possibility could be that hydrological variations controlling the supply of HCO3 - and Ca 2+ ions were less important for Fe and Si concentrations in water. This would imply a stronger dependence from rainfall fluctuations for the Ca content, whereas diatom growth (i.e. bSi content) would respond mostly to temperature variations, with superimposed fluctuations influenced by occasional Fe and Si inputs.

XRPD analyses of the bulk sediment reveal the predominant presence of calcite, accompanied only by a small amount of quartz. Quartz is typically present in small quantities in limestone. When carbonate rock dissolves, quartz remains in the soil together with other silicate minerals and Fe oxides and hydroxides.

These can be transported to the lake by runoff, which is enhanced when the vegetation cover is reduced.

Part of the quartz can also be linked to erosion and transport processes from silicate rocks in the lake catchment, but these rocks are virtually absent in the Sulmona Basin, thus their contribution is likely to be insignificant. Quartz can also have an aeolian origin, as suggested for quartz-rich loess deposits along the Apennines [START_REF] Giraudi | A Late-Pleistocene phase of Saharian dust deposition in the high Apennine mountains (Italy)[END_REF] and for quartz grains in central Italy maar lake sediments [START_REF] Narcisi | Late Quaternary eolian deposition in central Italy[END_REF]. Sourcing and transport of aeolian particles is also enhanced when the vegetation is less developed [START_REF] Boretto | Stratigraphy, pedological features, paleontology, geochemistry and chronology of the "loess-like" deposits of the Buca dei Corvi Section (central Italy)[END_REF]. Thus, at Sulmona the quartz/calcite ratio (Fig. 3) can be considered a simple, semiquantitative way to express variations in soil erosion in the catchment and/or in aeolian input to the lake, with higher ratios indicating decreased erosion and/or reduced aeolian transport, likely both arising from vegetation development under wetter and warmer conditions.

Paleoenvironmental and paleohydrological evolution during MIS 19 in the Sulmona Basin.

Based on the interpretations introduced above, the new high-resolution δ 18 O record for MIS 19c shows rapidly increasing precipitation after 788 ka (Fig. 3). This trend follows that observed in the lowresolution δ 18 O time-series by [START_REF] Giaccio | Duration and dynamics of the best orbital analogue to the present interglacial[END_REF]Fig. 3) and represents the latest part of the deglaciation occurring between MIS 20 and MIS 19. The deglaciation is accompanied by rising lake primary productivity (increasing Ca and bSi) and by enhanced supply of soil CO2 (lower δ 13 C), both indicating warmer temperature, and by a strong decrease in the clastic/aeolian input to the lake (decreasing qz/ct), likely arising from the increasing vegetation cover (Fig. 3). Peak precipitation was reached at ca.786.0 ka, but was rapidly interrupted by a prominent, ~0.8 kyr long, drier period starting at 785.6 ka (Fig. 3, Table 2). This event, denoted by the Roman number I in Figure 3 and in Table 2, is clearly expressed in all the other proxies. Precipitation increased again at 784.3 ka and remained relatively high until ca. 779.0 ka. Within this period, however, two events of reduced precipitation are apparent (II and III; Table 2, Fig. 3). Between 779 ka and 777 ka, precipitation and primary productivity decrease and conditions remain consistently drier and colder compared to the previous interval. Three further events of increasing dryness and reduced productivity occur between 779 ka and 775 ka (IV, V, VI; Table 2, Fig. 3). Aside from event I, changes of δ 18 O values during event II to VI are of low magnitude (0.2-0.4‰). However, all of them are coherently expressed by several data points (Fig. 3), suggesting that they represent a real short-term, low-amplitude hydrological variability. These events (II to VI) are not clearly expressed by the other proxies, likely due to their lower temporal resolution and to a more subdued response of these properties during period of overall wet conditions. From 773.0 ka, there is a large and abrupt decrease in precipitation, immediately followed by increased clastic input and reduced primary productivity lasting until 771.2 ka (event VII in Fig. 3, Table 2). This period is followed by an increase in precipitation and productivity (Fig. 3), although erosion rates in the catchment remain quite high until the end of the high-resolution section at 769.8 ka.

Regional significance of the Sulmona record and potential links with North Atlantic variability

Few paleoclimatic records spanning MIS 19c with a temporal resolution comparable to our record exist from the Mediterranean and the North Atlantic regions [START_REF] Nomade | High-resolution foraminifer stable isotope record of MIS 19 at Montalbano Jonico, southern Italy: a window into Mediterranean climatic variability during a low-eccentricity interglacial[END_REF][START_REF] Ferretti | The Marine Isotope Stage 19 in the mid-latitude North Atlantic Ocean: astronomical signature and intra-interglacial variability[END_REF][START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF], and none possesses an independent radiometric chronology. The coupled marine-pollen record from marine core U1385 on the southern Iberian Margin (Hodell et al., 2015;Sánchez-Goñi et al., 2016, Figs. 5 and6) provides a relatively high-resolution, multi-proxy biogeochemical record for the MIS 19 (resolution of ~300 yr for pollen and alkenones and of ~160-200 yr for planktonic and benthic stable isotope composition), capable of capturing both orbital and millennialscale climatic change [START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF]. The U1385 chronology relies on the climatostratigraphic tuning to the global benthic stack LR04, and has a mean absolute uncertainty of ~5 ka (Lisieki and Raymo, 2005). The benthic δ 18 O from U1385 shows that MIS 19 ranges from 791 ka to 758 ka, and that MIS 19c ends at ca. 775 ka. The pollen record from the same core shows that the onset of the terrestrial interglacial (Tajo interglacial) occurs at ca. 787 ka, slightly after the onset of MIS 19c, whereas its end is almost coincident with that of the benthic substage [START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF]. Seven events of forest contraction have been identified within MIS 19 (Sánchez-Goñi et al., 2016, Fig. 5). Of these, only those occurring after ca. 770 ka, i.e. well after the interglacial, appeared to be coupled with changes in oceanic conditions. For the other events, a warm sea/cold-dry land decoupling was observed and proposed to represent an increased latitudinal thermal contrast causing a northward shift in westerly wind trajectories. By analogy with the present positive mode of the NAO, this would have caused reduced precipitation over southern Iberia [START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF], and by extension in the central and eastern Mediterranean region (e.g. [START_REF] Regattieri | Middle Holocene climate variability from a stalagmite from Alilica Cave (Southern Balkans)[END_REF][START_REF] Smith | North Atlantic forcing of moisture delivery to Europe throughout the Holocene[END_REF]. Frequency analysis of the whole U1385 record shows evidence for a strong ~5-kyr periodicity [START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF]. This led to the conclusion that the variability observed in the pollen record can be attributed to precession harmonicsrelated changes in yearly solar radiation in the tropics, relaxing or amplifying the thermal latitudinal contrast and affecting mostly the strength of low-latitude low-pressure systems and thus atmospheric circulation [START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF].

The comparison between the Sulmona and the U1385 records reveals a striking similarity between the lacustrine δ 18 O and Mediterranean forest pollen percentage (Fig. 5). The intervals of forest reduction in the pollen record correspond to dry periods in the Sulmona record, where the higher resolution allows a better exploration of their internal structure and the identification of additional events (Fig. 5). Rainfall amount exerts a dominant control on the composition of southern European vegetation (e.g. Quezel et al., 2002;[START_REF] Gouveia | The North Atlantic oscillation and European vegetation dynamics[END_REF] and the oxygen isotope composition of Mediterranean continental carbonates (lacustrine sediment and speleothem; e.g. [START_REF] Bard | Hydrological conditions in the western Mediterranean basin during the deposition of Sapropel 6 (~175 kyr)[END_REF][START_REF] Roberts | Stable isotope records of Late Quaternary climate and hydrology from Mediterranean lakes: the ISOMED synthesis[END_REF], with forest expansion and 18 O-depleted precipitation associated with higher rainfall amount. This provides a basis for creating a common time scale between the Sulmona δ 18 O and the Iberian margin pollen records, an approach already employed to transfer the radiometric chronology of a central Italy δ 18 O speleothem record to a marine pollen record covering the Last Interglacial [START_REF] Tzedakis | Enhanced climate instability in the North Atlantic and southern Europe during the Last Interglacial[END_REF]. Thus, we aligned (sensu [START_REF] Govin | Sequence of events from the onset to the demise of the Last Interglacial: Evaluating strengths and limitations of chronologies used in climatic archives[END_REF][START_REF] Francke | Sedimentological processes and environmental variability at Lake Ohrid (Macedonia, Albania) between 637 ka and the present[END_REF] the peaks in Mediterranean pollen taxa corresponding to the Tajo interglacial and to the two subsequent forest expansions from U1385 to their analogous wet interstadials from the Sulmona δ 18 O record (Fig. 5 and SOM-Table 2). This adjustment produces minor shifts (average ~1.7 kyr) in the U1385 chronology, fully within the absolute chronological uncertainty, but it allows us to better constrain the age of Marine sub-Stage MIS 19c (starting at 791 ka) and that of the terrestrial interglacial as defined by [START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF] in southern Iberia (787.6 -776.9 ka). According to the Sulmona chronology, the Tajo interglacial in U1385 lasts 10.7 ± 2.8 ka, which is close to a half a precession cycle. A similar duration (i.e. 11.5 ± 3.4 kyr long) for the MIS19c interglacial was recently proposed by [START_REF] Nomade | High-resolution foraminifer stable isotope record of MIS 19 at Montalbano Jonico, southern Italy: a window into Mediterranean climatic variability during a low-eccentricity interglacial[END_REF] based on the marine section of Montalbano-Jonico (Southern Italy). The alignment between the U1385 pollen record and the Sulmona isotope record allows us to explore whether the dry events from Sulmona can be associated with changes in marine proxies (Fig. 6). It is worth noting that the resolution of stable-isotope analyses from both archives is higher than that of the pollen and SST records, permitting a more detailed sea-land comparison once a common time scale is defined. For the major events occurring at ca. 772 ka, 765 ka and 760 ka based on the Sulmona chronology (VII, IIX and IX in Fig. 6), rainfall reductions are in phase with prominent changes in oceanic conditions, i.e. decreasing benthic δ 13 C and sea surface temperature (SST), increasing planktonic δ 18 O and C37:4 -based freshwater index, Fig. 6). These events have been correlated to intervals of sub-polar Ice Rafted Debris (IRD) deposition [START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF]. The freshwater flux associated with IRD deposition is known to induce intervals of AMOC slow-down or interruption (e.g. [START_REF] Mcmanus | A 0.5-million-year record of millennial-scale climate variability in the North Atlantic[END_REF]. The resulting decrease in SST at the mid-latitudes reduced evaporation and advection of air masses rich in moisture towards the Mediterranean region, leading to basin-wide colder and drier intervals during glacial and transitional periods (i.e., glacial/interglacial transition and glacial inception), (e.g. [START_REF] Drysdale | Stalagmite evidence for the precise timing of North Atlantic cold events during the early last glacial[END_REF][START_REF] Fletcher | A centennial-scale record of vegetation and climate variability from 312 to 240 ka (Marine Isotope Stages 9c-a, 8 and 7e) from Tenaghi Philippon, NE Greece[END_REF][START_REF] Margari | Character of vegetational and environmental changes in southern Europe during the last glacial period; evidence from Lesvos Island, Greece[END_REF][START_REF] Regattieri | Hydrological variability over the Apennines during the Early Last Glacial precession minimum, as revealed by a stable isotope record from Sulmona Basin, Central Italy[END_REF][START_REF] Regattieri | A multi-proxy record of MIS 11-12 deglaciation and glacial MIS 12 instability from the Sulmona Basin (central Italy)[END_REF][START_REF] Sinopoli | Palynology of the Last Interglacial Complex at Lake Ohrid: palaeoenvironmental and palaeoclimatic inferences[END_REF][START_REF] Tzedakis | Ecological thresholds and patterns of millennial-scale climate variability: The response of vegetation in Greece during the last glacial period[END_REF]. Together with reduced precipitation, for the event at ca. 772 ka the other proxies from Sulmona also show marked decreasing primary productivity in the lake and in the surroundings soils, coherently indicating decreasing temperatures (Fig. 3).

For events not associated with iceberg discharges in the North Atlantic (I to VI in Fig. 6), marine proxies do not show major oscillations, but rather a low-amplitude variability (Fig. 6). The event I at ca. 786 ka appears to correspond to a decrease in planktonic δ 18 O comprising several data points, followed by a similar increase (Fig. 6). Further, the benthic δ 13 C and the SST records show coincident slightly decreasing values (Fig. 6), suggesting that this event may be connected to a slight weakening of AMOC activity. To some extent, a similar configuration is apparent also for the event at ca. 782 ka (Fig. 6), although it is not expressed by the benthic δ 13 C record. For the other events, the relatively low resolution and the low intensity variability hampers the possibility of a detailed correlation, though slightly increased planktonic δ 18 O values seem to correspond to event VI (Fig. 6).

To better define the relationship between Mediterranean hydrology and ocean conditions during the interglacial, we compare our δ 18 O record to the high-resolution (average 250 years) multiproxy record from ODP-983 from the Gardar Drift, south of Iceland (Figs. 1 and 8, [START_REF] Kleiven | Coupled deep-water flow and climate variability in the middle Pleistocene North Atlantic[END_REF]. The Gardar Drift is a key location to assess changes in NADW formation and related perturbations of AMOC circulation [START_REF] Kleiven | Atlantic Ocean thermohaline circulation changes on orbital to suborbital timescales during the mid-Pleistocene[END_REF][START_REF] Kleiven | Coupled deep-water flow and climate variability in the middle Pleistocene North Atlantic[END_REF]. There, changes in deep hydrography are highlighted by decreases in outflow speed and intensity from the Nordic Sea, recorded by changes in sediment grain size and sorting [START_REF] Kleiven | Coupled deep-water flow and climate variability in the middle Pleistocene North Atlantic[END_REF][START_REF] Mccave | Size sorting in marine muds: Processes, pitfalls, and prospects for paleoflow-speed proxies[END_REF] and by fluctuations in the benthic δ 13 C record [START_REF] Oppo | Mid-depth circulation of the subpolar north Atlantic during the last glacial maximum[END_REF]. During warm periods, the site is bathed at depth by the vigorous outflow of the Iceland-Scotland Overflow Water (ISOW), an essential component of the AMOC circulation that modulates European climate [START_REF] Bianchi | Hydrography and sedimentation under the deep western boundary current on Björn and Gardar Drifts, Iceland Basin[END_REF]. Warm salty surface waters are advected northward, where the site of deep convection and NADW formation is located [START_REF] Knorr | Rapid transitions in the Atlantic thermohaline circulation triggered by global warming and meltwater during the last deglaciation[END_REF][START_REF] Schmidt | Links between salinity variation in the Caribbean and North Atlantic thermohaline circulation[END_REF]. At site 983 interglacial circulation appears substantially more stable compared to glacial periods, when the centre of NADW formation shifted from the present Nordic Seas position to the subpolar North Atlantic [START_REF] Oppo | Mid-depth circulation of the subpolar north Atlantic during the last glacial maximum[END_REF]. However, all the warm stages of the Middle Pleistocene show the occurrence of rapid shifts in the style or intensity of deep-water convection, implying internal mechanisms that may generate AMOC instabilities also during periods of low icevolume [START_REF] Kleiven | Atlantic Ocean thermohaline circulation changes on orbital to suborbital timescales during the mid-Pleistocene[END_REF].

We first exported our independent chronology to the marine record. As discussed, events of IRD deposition in the North Atlantic impact AMOC circulation and, as a consequence, the Mediterranean hydrological cycle. Thus, we align the end of the IRD peaks occurring during the glacial inception to the corresponding onset of wet interstadials in our record (Fig. 7 and SOM-Table 2), and the end of the last IRD peak occurring during the glacial termination with the onset of the terrestrial interglacial (Fig. 8 and SOM-Table 2). As an independent test for alignment, we consider the correlations between U1385 and ODP-983, both reported on the Sulmona chronology (Fig. 7). The onset and demise of the major intervals of IRD deposition in the subpolar region show good chronological agreement with intervals of increased C37:4 based fresh-water index (Fig. 7), despite the low resolution of the latter curve. Also, the stadialinterstadial pattern of the two planktonic δ 18 O time-series is consistent. Decreasing/increasing δ 18 O planktonic values can be linked to increasing/decreasing temperature or to decreased/increased salinity.

In the ODP-983 record, IRD events are accompanied by decreasing planktonic δ 18 O values (Fig. 7), likely due to the influence of 18 O-depleted meltwater releases, whereas on the Iberian margin the freshwater flux is associated with decreasing SST and related increases of planktonic δ 18 O values (Fig. 7). Now that a common time scale is defined, we can check in detail if intra-interglacial continental events have a counterpart in the sub-polar record (Fig. 8). As with U1385, the ODP-983 record shows only a subdued variability during the interglacial. However, the event I at ca. 786 ka is marked by a significant reduction in deep-water ventilation (lower benthic δ 13 C), and by a decrease in outflow strength (lower sortable silt percentage; Fig. 8), suggesting the occurrence of a short-term AMOC perturbation. It also corresponds to a slight and steep decrease and a subsequent sudden increase in planktonic δ 18 O (Fig. 8).

The other events recorded at Sulmona do not clearly correlate with variations in ODP-983 proxies due to the subdued variability of the latter record. However, considering the combined age uncertainties, a similar pattern between the deep outflow from the Nordic Sea (represented by the sortable silt percentage, Fig. 8) and the Sulmona δ 18 O record is apparent. Fluctuations in the sortable silt percentage are small, but a similar variability observed during the Holocene in the record of nearby marine core NEAP-15K [START_REF] Bianchi | Hydrography and sedimentation under the deep western boundary current on Björn and Gardar Drifts, Iceland Basin[END_REF] has been considered significant, and interpreted as reflecting subtle changes in the ISOW strength.

Forcing and pacing for millennial-to-centennial-scale variability during the MIS 19

Our analyses point to different forcing for millennial and sub-millennial variability during MIS 19. After the interglacial and following 772 ka, coherent changes in marine and continental proxies (Figs. 6 and8) indicate a rapid transfer of northern North Atlantic climate changes into the western Mediterranean region. The North Atlantic record suggests that this variability arises from interactions between ice-sheet dynamics (testified by the IRD-C37:4 events) and the AMOC. Within the interglacial, event I centred at ca. 786 ka also shows a coupling between continental and marine conditions (Figs. 6 and8). This rainfall reduction and forest contraction in southern Europe appears to be related to a temporary, low-intensity AMOC disturbance. The marine records show lower benthic δ 13 C at both sites, decreased SST on the Iberian Margin, and reduced convection in the northern North Atlantic (Figs. 6 and8). Concomitant decreasing δ 18 O planktonic values in the marine records can be related to increasing temperature, which is in contrast with the SST record from the Iberian margin, or to decreased salinity, potentially related to freshwater influx. This evidence suggests that this event could be an analogue to the Holocene 8.2 ka event, i.e., the final outburst from the proglacial lake Agassiz (e.g. [START_REF] Alley | Holocene climatic instability: A prominent, widespread event 8200 yr ago[END_REF]Alley and Angustsdottir, 2005;[START_REF] Barber | Forcing of the cold event of 8,200 years ago by catastrophic drainage of Laurentide lakes[END_REF][START_REF] Clarke | Paleohydraulics of the last outburst flood from glacial Lake Agassiz and the 8200 BP cold event[END_REF]. The related freshening of surface water impacted convection in the Labrador Sea, where the western centre of NADW production is located, producing a slowdown of the AMOC, and a consequent widespread climate anomaly. The occurrence of similar events has been also postulated for interglacials other than Holocene, as for the Last Interglacial [START_REF] Nicholl | A Laurentide outburst flooding event during the last interglacial period[END_REF][START_REF] Galaasen | Rapid reductions in North Atlantic deep water during the peak of the last interglacial period[END_REF], and the MIS 11 [START_REF] Koutsodendris | A short-term climate oscillation during the Holsteinian interglacial (MIS 11c): An analogy to the 8.2 ka climatic event?[END_REF]. Interestingly, although the lower resolution and the chronological mismatching prevent a secure correlation, a shortlived period of climate perturbation is apparent within several MIS 19c records. Indeed, a cooling event in the early part of the interglacial has been reported from the pollen record of the Montalbano Jonico section (Southern Italy, [START_REF] Bertini | Vegetation and climate across the Early-Middle Pleistocene transition at Montalbano Jonico, southern Italy[END_REF]Marino et al., 2015), and from a marine core from the Osaka Bay (Japan, [START_REF] Maegakiuchi | Brief sea-level fall event and centennial to millennial sea-level variations during Marine Isotope Stage 19 in Osaka Bay, Japan[END_REF]. For the other intra-interglacial events, the coupling between terrestrial and marine proxies, especially those from the Iberian Margin, is not as clear, perhaps pointing to a different forcing. Changes in north-westerly circulation and related moisture transport are likely involved, but the ultimate causes for these atmospheric oscillations remain currently largely unexplained.

To explain changes in local convection observed at the ODP-983 site during interglacial intervals, it has been proposed that enhanced sea-ice formation south of Iceland might have created an unstable density stratification in the water column, causing a slow-down in the advection of southern warm waters, and an attendant cooling over the northern North Atlantic, with a downstream effect amplified by changes in the atmospheric circulation [START_REF] Kleiven | Coupled deep-water flow and climate variability in the middle Pleistocene North Atlantic[END_REF]. State-of-the-art coupled models also have shown the occurrence of positive feedbacks between the atmosphere and the sea-ice, with stochastic atmospheric changes inducing AMOC weakening and larger sea-ice cover, leading to cooling in the sub-polar and to strengthening of high-pressure system at the high latitudes [START_REF] Drijfhout | Spontaneous abrupt climate change due to an atmospheric blocking-sea-ice-ocean feedback in an unforced climate model simulation[END_REF][START_REF] Kleppin | Stochastic atmospheric forcing as a cause of Greenland climate transitions[END_REF].

The similarity between the oxygen record from Sulmona and the record of deep-water ventilation and outflow speed from the Nordic Sea (Fig. 8) suggests that this cooling impacted atmospheric circulation patterns also in the Mediterranean by altering the intensity and trajectories of westerly winds. In particular, it would have led to a northern shift of the westerlies, reducing their penetration, and thus the amount of rainfall, within the Mediterranean Basin. This would have resembled an atmospheric configuration similar to the positive state of the NAO.

Further insights on the ultimate forcing for the MIS 19 millennial and sub-millennial variability can be obtained from the dominant periodicities resulting from the Sulmona CWT analyses and by analysing the timing and pacing of events. The real wavelet power spectrum for the oxygen time series, including low-resolution data from [START_REF] Giaccio | Duration and dynamics of the best orbital analogue to the present interglacial[END_REF] for the younger (i.e. after 770 ka) and older portions (prior to 790 ka) of the record, is shown in Fig. 9. Both the spectrum and the curves for the most energetic periodicities (Fig. 9) show prominent changes throughout the investigated period and especially between the transitional periods (deglaciation and glacial inception) and the interglacial portion of the record.

Considering only those periodicities which i) are enclosed in the region of greater than 95% confidence, ii) fall above the COI and iii) are longer than the uncertainty associated to the record (median 2.5 kyr), two main wavelength bands can be recognized. Starting from the longest, a ~5.0-6.0 kyr cycle (Fig. 9) can be observed throughout the investigated period. Periodicities of ca. 5-6 kyr, i.e. similar to the fourth precession harmonic have been observed in several MIS 19 records [START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF][START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF][START_REF] Weirauch | Evolution of millennial-scale climate variability during the mid-Pleistocene[END_REF][START_REF] Nomade | High-resolution foraminifer stable isotope record of MIS 19 at Montalbano Jonico, southern Italy: a window into Mediterranean climatic variability during a low-eccentricity interglacial[END_REF]. However, in our record the intensity of this periodicity almost vanishes in the middle portion of the interglacial, especially between ca. 784 and 778 ka (Fig. 9). Further, the pacing of both intra-and post-interglacial events is non-stationary, ranging from ca. 4 to 2 kyr (Table 2). The non-stationarity is evident whatever approach is used to define the temporal relationships among different events, i.e. either when the onset, the mid-point and the end of events are considered. The length of events is also rather variable (Table 2), with an average duration between 0.9 and 0.6 kyr within the interglacial and 2.3 kyr for the early glacial (Table 2). Although our observation cannot rule out an initial forcing by precession harmonics, that can be modulated by sea-ice changes and may affect the timing of the millennial scale variability by producing non-stationary cycles throughout the MIS 19 (Ferretti et al., QSR, 2015), the observation that intra-interglacial events occur too often to be explained by a 5-6 kyr cyclicity, suggest that a precession forcing is likely not the cause of intrainterglacial events apparent in the Sulmona record.

Another significant periodicity of between ca. 4.2 and 3.5 kyr is also evident (Fig. 9), but its intensity is also reduced during the MIS 19c, again suggesting that forcing of millennial and sub-millennial scale variability changed between interglacial and transitional periods.

Conclusions

In this work, we have presented a multiproxy record (high resolution stable carbon and oxygen isotope, low resolution elemental and mineralogical composition, and biogenic silica content) obtained from endogenic lacustrine sediments of the Sulmona Basin (central Italy). The record is anchored onto a fully independent time-scale based on 40 Ar/ 39 Ar dating of six tephra layers interbedded in the lacustrine sediment, and covers the ca. 790-770 ka period, thus encompassing the interglacial portion of Marine Isotope Stage MIS 19,. Hydrological and environmental proxies coherently indicate that the post-interglacial period is marked by major changes in climatic and environmental conditions. Within the MIS19c interglacial, a low-intensity, though significant, centennial-to millennialscale hydrological and environmental variability is present and shows a non-stationary pacing. In particular, a major event of rainfall reduction and environmental deterioration, ~ 1 kyr long, occurred at ca. 786 ka according to our age model. Comparison of the Sulmona record with records from the Iberian margin [START_REF] Sánchez-Goñi | Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial[END_REF] and from the sub-polar North Atlantic [START_REF] Kleiven | Coupled deep-water flow and climate variability in the middle Pleistocene North Atlantic[END_REF], both reported on the radiometric Sulmona chronology through paleoclimatic alignment (sensu [START_REF] Govin | Sequence of events from the onset to the demise of the Last Interglacial: Evaluating strengths and limitations of chronologies used in climatic archives[END_REF] points to different mechanisms operating in different periods. Major dry events on land occurring after the end of the interglacial are associated with AMOC disruptions and increased iceberg discharge in the sub-polar north Atlantic. Within the interglacial (ca. 788-777 ka), the event at ca. 786 ka also appears related to a lower intensity perturbation of the oceanic circulation. Other intra-interglacial events are not so clearly associated with changes in marine proxies, though similarities with the sub-polar record suggest a link between rainfall amount is southern Europe and deep hydrography in the northern North Atlantic. We propose that changes in local convection, potentially related to feedbacks between atmosphere and sea-ice, may have created unstable density stratification conditions, which may have impacted the westerly circulation and the related moisture transport over the Mediterranean Basin.

Noteworthy, for MIS 19 as a whole, a higher global ice volume was proposed based on modelled global sea level [START_REF] Bintanja | Modelled atmospheric temperatures and global sea levels over the past million years[END_REF][START_REF] Bintanja | North American ice-sheet dynamics and the onset of 100,000year glacial cycles[END_REF]. Possibly, this configuration would have caused a more pronounced "glacial" character for the MIS 19c interglacial, with larger global ice volume influencing dynamics and intensity of deep convection in the eastern North Atlantic, with downstream influences on rainfall variability over southern Europe. This suggests that also small changes in boundary conditions (and particularly of ice-volume and temperature) can strongly influence the millennial-scale climate variability during interglacial periods. counting*sec); D) Biogenic silica content (% wt); E) Ratio of peak areas of quartz and calcite XRD analyses. Grey shadings indicate events of reduced precipitation, roman numbers are as in Table 2. Yellow shadings indicate the events of forest contraction identified by Sanchez-Goni et al., (2016) as well as the Tajo interglacial as apparent from the same record. Grey shadings are events of reduced precipitation as defined in Fig. 3 2). Grey rectangles are as from Table 2 and Fig. 3 and indicates events of reduced precipitation in the Sulmona basin. the cone of influence. It delimits the spectrum in two regions, where the portion below the black line may be affected by edge effects and thus shows frequencies that are not significant considering the total length of the record (Tognarelli et al., 2018b). The contour delimited by the black line encloses the area with a confidence greater than 95%. Upper panel: the series reconstructed considering 5-6 and 4.2-4.5 kyr periodicities.

Figure 4 -

 4 Figure 4-Correlation plots of δ 13 C and δ 18 O composition

Figure 6 -

 6 Figure 6-Comparison between Sulmona δ 18 O (a, light line is the lower resolution series from Giaccio et al. (2015) and the U1385 record (Sánchez-Goñi et al., 2016) on the Sulmona chronology; b) U1385 Mediterranean forest pollen percentage; c) U1385 planktonic δ 18 O; d) U1385 benthic δ 13 C; e) U1385 Alkenones Sea Surface Temperature; F) U1385 percentages of alkenone C37:4. The top panel shows the U1385 benthic δ 18 O record and MI stages and substages division. Roman numbers indicate the events of reduced precipitation from the Sulmona record (see Table2). Grey rectangles are as from Table2 and

Figure 7 -

 7 Figure 7-Upper panel: tuning of the IRD record from core ODP-983 (Light-blue solid plot, on the original chronology by Kleiven et al., 2010) on Sulmona δ 18 O time series (this study and Giaccio et al., 2015). Red circles indicate selected alignment points. Lower panel: comparison of U1385 (green, planktonic δ 18 O‰ and C37:4 based freshwater index) and ODP-983 (blue, planktonic and IRD) records, both reported on the Sulmona chronology. Grey rectangles indicate the intervals of IRD deposition in the North Atlantic.

Figure 8 -

 8 Figure 8-Comparison between Sulmona δ 18 O and the ODP-983 record (Kleiven et al., 2011) reported on the Sulmona chronology; b) ODP-938 Sortable silt percentage; c) ODP-983 planktonic δ 18 O; d) ODP-983 benthic δ 13 C; Roman numbers and grey rectangles indicate the events of reduced precipitation from the Sulmona record and are as shown in Table2 and Figure 3.

Figure 9 -

 9 Figure 9-Lower panel: Sulmona oxygen isotope real wavelet spectrum. The lower black line indicates

Figure

  Figure S1-FESEM images of Sulmona lacustrine sediment.

  and Table 2. Dotted grey lines indicate proposed correlations between Sulmona and U1385 events.

Acknowledgement

This work has been developed in the frame of the project HELPING (Hydrological Evolution of Past INterGlacial), funded by the National Geographic Society through an Early Career Grant assigned to E. R (CP-073ER-17). It was also part of project PRA_2018_41 "Georisorse e Ambiente" funded by the University of Pisa. 40 Ar/ 39 Ar dating was funded by the SYSTER program (INSU CNRS) assigned to S. N (ChronoBM project). ER, GZ, RND and PCT were also supported by an Australian Research Council Discovery Projects grant (DP160102969). PCT acknowledges funding from the UK Natural Environment Research Council (grant NE/ I025115/1). GZ, BG and GM acknowledges funding from MIUR-PRIN 2017 "Future" (leader GZ), The authors thank M.F. Sanchez-Goni, D. Hodell and T. Rodrigues for providing data for comparison, and acknowledge C. Gini, A. Chitula Moura and N. Vivoli for help with XRPD and J. Krbanjevic with FTIRS sample preparation and data acquisition. Ola Kwiecien and three other anonymous reviewers are acknowledged for their useful comments which substantially improved the quality of the manuscript.

Tables and Figure Captions

Table 1-Names, ages, uncertainties and depths of tephra layers used in the age-depth modelling procedure. Grey cells indicate tephra occurring within the interval discussed here. *Age from [START_REF] Giaccio | Duration and dynamics of the best orbital analogue to the present interglacial[END_REF]; ** age from this study.

Table 2--Age, length and pacing for events of reduced precipitation as from the Sulmona record. Roman numbers are as in Figs. 3, 7 and9; events reported in italics are from the low-resolution series from [START_REF] Giaccio | Duration and dynamics of the best orbital analogue to the present interglacial[END_REF].