Papers by Stephanie Desprat
Developments in Quaternary Science, 2007
... of carpinus betulus, at around 121 kyr BP, quantitative climate reconstruction reveals that a... more ... of carpinus betulus, at around 121 kyr BP, quantitative climate reconstruction reveals that a substantial cooling, by 2 C, took place at around 118 kyr BP (Sanchez Goi et al., 2005 ... In: Haupt, BJ, Maslin, MA (Eds.), The Oceans and Rapid Climate Changes: Past, Present and future. ...
A synthesis of the multiproxy studies achieved on three twin deep-sea cores from the NW Iberian m... more A synthesis of the multiproxy studies achieved on three twin deep-sea cores from the NW Iberian margin and providing a record spanning several climatic cycles up to 425 kyrs will be presented. They include records of pollen and marine tracers (assemblages of planktic foraminifera providing sea surface temperature estimates, planktic and benthic δ18O measurements) enabling a direct comparison between the vegetation and climate changes on land and the marine environment variations of the North Atlantic mid-latitudes and adjacent landmasses. This compilation gives information on the variability of duration and degree of warming of past interglacial periods which occurred under different combinations of baseline climate states related to astronomical forcing, ice volume and greenhouse gas concentrations. For example, forested stage of MIS 11 (centered on 400 ka, and known as the closest analogue of our interglacial due to Earth’s orbital configuration) appears to be the longest of the last 425 kyrs, twice as long as the Eemian in NW Iberia. The Iberian margin records also provide additional evidence of pervasive millennial-scale climatic variability in the North Atlantic borderlands throughout past climatic cycles of the Late Pleistocene, regardless of glacial states. A focus on MIS 9 showed however that ice volume might have an indirect influence on the amplitude of the millennial climatic changes in Southern Europe.
We present a new direct land-sea correlation covering the last deglaciation in order a) to provid... more We present a new direct land-sea correlation covering the last deglaciation in order a) to provide a better documentation of the regional vegetation changes in southeastern North America and b) more particularly to assess the connection of the continental climatic changes to North Atlantic circulation rapid variability. It was achieved using coupled analyses of pollen and marine climatic proxies from core KNR140-GGC39 (Blake Outer Ridge) at very high time-resolution. Mg/Ca ratio, planktonic δ18O, mean "sortable silt" grain size (mean S¯S¯) were analyzed in order to get records of SST, salinity and bottom current strength at the core site (Evans et al., submitted to Paleoceanography). The abrupt climatic changes which characterize the last deglaciation, in particular the major cold oscillations Heinrich event 1 (H1) and Younger Dryas (YD), have been widely documented in the North Atlantic and adjacent continents. However, in the tropical and subtropical North Atlantic and southeastern United States, the climatic signature of these events appears quite different and somehow unclear. Our direct land-sea correlation shows three configurations: 1- H1 period: cold climatic conditions in southeastern US (high percentages of boreal and herbaceous taxa) but only extremely cold at around 17 ka, accumulation of salty water in the subtropics (high δ18OSW- IVC) and weak bottom current intensity at the site (low mean S¯S¯) 2- Bolling Alleröd interval: abrupt warming in southeastern US (decrease of boreal taxa in favour of Quercus) at the beginning, synchronous to northern export of the salty water previously accumulated and to an increase of the bottom current strength at the site 3- YD period: mild and wet conditions in southeastern US (expansion of Tsuga and Quercus), decrease of the bottom current strength at the site and accumulation of salty water in the subtropical regions but less than during H1.
Last glacial abrupt climate changes, defined as Dansgaard/Oeschger variability (D/O) and Heinrich... more Last glacial abrupt climate changes, defined as Dansgaard/Oeschger variability (D/O) and Heinrich events (HE), have been documented in ice cores, marine sediments and continental deposits, generally from the Northern Hemisphere (Voelker et al., 2002). While most North Atlantic paleoceanographic and paleoclimatic studies covering the last glacial period are centred in the northern and eastern part (Voelker et al., 2002), less attention has been paid to the western midlatitudes (López-Martínez et al., 2006; Vautravers et al., 2004). In particular last glacial eastern North American vegetation changes remain poorly unknown due to a lack of long continuous pollen records in this region. So far, only two pollen sequences from Lake Tulane (Florida) show significant and interesting vegetation changes during the last glacial period (Grimm et al., 1993 and 2006) which suggest warm and humid HE, contrasting with what is observed in the eastern part of the North Atlantic (Sánchez Goñi et al., 2000). In this work we present the first high resolution reconstruction of the vegetation changes derived from the analysis of a pollen-rich marine core located in the subtropical western North Atlantic (MD99-2203, 34°58'N, 75°12'W, 620 m water depth) during Marine Isotope Stage 3 (MIS3). A clear alternation between Picea and Quercus is showed by pollen data from core MD99-2203. In general, pollen assemblages indicate last glacial vegetation variations following a boreal forest/mesic-Quercus forest pattern that could be associated with the D/O variability. A preliminary age model based on radiocarbon ages suggests an increase of temperate forest accompanied by a reduction of the boreal forest during Greenland interstadials (López-Martínez et al., in preparation). Comparison with other proxies measured in the same core (d18O and alkenone and planktonic foraminifera derived sea surface temperature) and with published high resolution marine pollen records from the eastern subtropical region (Sánchez Goñi et al., 2000; Naughton et al., submitted) provide better understanding of the impact of millennial scale climate variability over the last glacial period in the subtropical North Atlantic. The pollen sequence from core MD99-2203 shows, for the first time, that changes in forest formations associated with last glacial abrupt climate changes were smoother in south-eastern North America than in the Iberian Peninsula (López-Martínez et al., in preparation) Grimm et al., 1993. Science, 261: 198-200. Grimm et al., 2006. Quat. Sci. Rev., 25: 2197-2211. López-Martínez et al., 2006. Paleoceanography, 21: PA4215, doi:10.1029/2006PA001275. Naughton et al., Earth Planet. Sci. Lett., submitted. Sánchez Goñi et al., 2000. Quat. Res., 54: 394-403. Vautravers et al., 2004. Paleoceanography, 19(PA2011): doi:10.1029/2003PA000966. Voelker et al., 2002. Quat. Sci. Rev., 21: 1185-1212.
Recent models and data synthesis suggest that the Last Interglacial North Atlantic warm optimum, ... more Recent models and data synthesis suggest that the Last Interglacial North Atlantic warm optimum, ~130 ±2 ka, corresponded with a sea level stand of 4-9 m higher than that of the present-day implying that a substantial part of the Greenland Ice Sheet (GIS) melted at that time. This makes this interglacial a good analogue for understanding the impact of the ongoing global warming and GIS melting on the Atlantic Meridional Overturning Circulation (AMOC) and adjacent landmasses. Here we provide new insights on the impact of insolation and AMOC changes on western European ecosystems and climate and their regional transmission during an episode of GIS melting that can be considered somehow similar to that predicted for 2100 C.E. from IPCC projections. We have revisited three pollen-rich western European margin sequences distributed from 37 to 45°N, MD04-2845, MD95-2042 and MD99-2331, which span all of MIS 5 and are directly affected by the descending branch of the North Atlantic Drift. The analysis of these sequences allows us to directly correlate marine tracers of AMOC variability and changes in ice volume, sea surface temperature (SST), iceberg discharges and pollen-derived European vegetation and climate. The comparison of these observations with those inferred from other locations in the North Atlantic region directly affected by the AMOC and records from the Eirik Drift off southern Greenland document the response of North Atlantic climate to GIS melting during the Last Interglacial. Large and rapid increase in the Western European forest cover and mid-latitude North Atlantic SST at the beginning of MIS 5e benthic isotopic plateau following the YD-like event coincide with strong GIS melting. Despite continued GIS melting during this interval, AMOC strength gradually increases. The dramatic expansion of western European forest could be the result of both AMOC and insolation increase. Subsequently sustained warm SSTs and strong AMOC do not preclude the long term forest reduction which parallels insolation decrease. On millennial time scales, repeated decreases in GIS runoff occurred when Europe and the adjacent ocean cooled and AMOC strength weakened. Contrary to what would be expected if GIS melting triggering reduced AMOC with attendant forest reductions and cooling in western Europe and the North Atlantic Ocean, our study suggests that GIS melting increases at the same time as the subpolar and mid latitudes of the North Atlantic and adjacent landmasses experienced warming with AMOC reinvigoration. Given the potential analogue between the Last Interglacial and the end of this century, we suggest that in contrast to GIS melting weakening AMOC, increased radiative forcing leading to future GIS melting may be associated with increased AMOC strengthwarming of Western Europe and a larger extent of temperate forests, in the absence of human intervention.
We present a multi-proxy record from the marine core MD04-2797CQ, including pollen, alkenone-base... more We present a multi-proxy record from the marine core MD04-2797CQ, including pollen, alkenone-based sea surface temperatures (SST), planktonic foraminifera assemblages and derived SST, dinocyst associations, planktonic carbon and oxygen stable isotopes. This core was retrieved from the Siculo-Tunisian Straight in the Central Mediterranean. The coupled marine and terrestrial proxy analyses enable to correlate without chronological ambiguities the vegetation and climatic changes in Sicilia and mainly Northern Tunisia to the Central Mediterranean Sea environment variations. This study seeks to characterize the nature and amplitude of terrestrial and marine ecosystem changes in the Central Mediterranean region in response to orbital and millennial climatic variability during the current interglacial. The Mediterranean is one of the most sensitive regions to future climate change (Giorgi, 2006); a strong aridity increase by the end of the century is predicted by most of the models using the IPCC scenarios (IPCC report, 2007). The presented direct land-sea correlation will contribute to tackle the marine and atmospheric mechanisms controlling the orbital and abrupt hydrological changes in the Mediterranean. The marine pollen sequence MD04-2797CQ records long term changes in seasonal precipitation during the Holocene. The marine proxies show contemporaneous variations of the Mediterranean Sea environments as well as several abrupt changes. Interestingly, while pollen assemblage percentages do not reveal pervasive Holocene abrupt vegetation variability, the pine frequencies display clear recurrent oscillations which are apparently coeval with the millennial Holocene North Atlantic changes. These fluctuations probably reflect changes in the pine pollen supply to the Central Mediterranean which is mainly controlled by atmospheric circulation. They would mirror the reorganization of the ocean-atmosphere system associated with Holocene abrupt climate changes.
The high-temporal resolution pollen record from the Alboran Sea ODP Site 976, and associated poll... more The high-temporal resolution pollen record from the Alboran Sea ODP Site 976, and associated pollen-based quantitative climate reconstruction and biomisation show that Mediterranean vegetation changes have been clearly modulated by short and long term variability during the last 25,000 years. The reliability of the quantitative climate reconstruction from marine pollen spectra using the Modern Analogue Technique (MAT) has been tested on 22 marine core-top samples from the Mediterranean. Although the MAT seems to slightly underestimate the winter temperatures and overestimate the winter precipitation, the present-day observed and MAT estimations show an adequate consistency, in particular for summer temperatures and annual and summer precipitation. According to these results, the MAT appears as a valuable approach to quantify the past climatic changes on land from marine Mediterranean pollen records. The ODP Site 976 pollen record and associated climatic reconstruction confirm that Mediterranean environments have a rapid response to the abrupt climatic changes of the last Termination such as Heinrich event 1, Bölling/Allerød and Younger Dryas and even the centennial cold event, Older Dryas, within the Bölling/Allerød period. The western Mediterranean vegetation and North Atlantic changes appear nearly synchronous. In contrast to the general warming climatic trend shown in Greenland and north European records (Rasmussen et al., 2006, 2007; Lowe et al., 2008; von Grafenstein et al., 1999), the ODP Site 976 pollen record shows a cooling trend during the Bölling/Allerød period. During the Holocene, recurrent declines of the forest cover over the Alboran Sea borderlands (southern Spain and northern Morocco) indicate abrupt climatic changes that correlate well with several events of increased Mediterranean aridity previously observed on land (Jalut et al. 2002) and with Mediterranean Sea cooling episodes detected by alkenone and foraminifer -based sea surface temperature records from other Mediterranean cores (Cacho et al., 2001; Frigola et al., 2003). They also are timely correlated to the Holocene North Atlantic cold events (Bond et al, 2001). This suggests the rapid response of the western Mediterranean vegetation to the Holocene short-time climate events and reflects the large ocean-atmosphere coupling.
Developments in Quaternary Science, 2007
The last five isotopic interglacials (marine isotope stages 11, 9, 7, 5 and 1) were investigated ... more The last five isotopic interglacials (marine isotope stages 11, 9, 7, 5 and 1) were investigated in Iberian margin deep-sea cores, using terrestrial (pollen) and marine (planktic foraminifera assemblages, benthic and planktic oxygen isotopes) climatic indicators. This work shows that the climatic variability detected on the continent is contemporaneously recorded in the ocean, but temperature changes are not in phase with ice volume variations. The comparison of the different marine isotope stages highlights a common pattern within these stages. They are characterized by three major climatic cycles, related to orbital cyclicity, on which suborbital climatic fluctuations are superimposed. Particularly, suborbital events interrupt the deglacial warming associated with Terminations IV to I and the second major warm period of each isotopic interglacial as well as the transitions towards glacial marine isotope stages. MIS 7 displays a short first warm period ($ 8 kyr) followed by a striking cold and dry period succeeded by a new strong warmth. In contrast, MIS 11 presents the longest period ($ 31 kyr) of the last 450 000 years.
Earth and Planetary Science Letters, 2009
surface temperature variability during the last glacial-interglacial cycle: assessing the magnitu... more surface temperature variability during the last glacial-interglacial cycle: assessing the magnitude and pattern of climate change in the North Atlantic. Palaeogeography-Palaeoclimatology-Palaeoecology, 157: 1 -25.
Quaternary Science Reviews, 2005
The Marine Isotope Stage 11 interglacial, centred at $400 ka, appears to be the best candidate fo... more The Marine Isotope Stage 11 interglacial, centred at $400 ka, appears to be the best candidate for understanding climatic changes in the context of low insolation forcing such as that of our present interglacial. Direct correlation between terrestrial (pollen) and marine climatic indicators and ice volume proxy from deep-sea core MD01-2447 (off northwestern Iberia) shows for the first time the phase relationship between southwestern European vegetation, sea surface temperatures in the northeastern Atlantic midlatitudes and ice volume during MIS 11. A warmest 32,000 years-long period and three following warm/cold cycles occurred synchronously on land and ocean. The end of the warmest period sees the glacial inception which coincides with the replacement of warm deciduous forest by conifer (pine-fir) expansion in northwestern Iberia and, consequently, with the southward migration of the tree line in high latitudes in response to declining summer insolation. As weak insolation changes alone cannot account for ice growth, the associated vegetation changes must now be considered as a potential major feedback mechanism for glaciation initiation during MIS 11. r
Marine Micropaleontology, 2007
The comparison between modern terrestrial and marine pollen signals in and off western Iberia sho... more The comparison between modern terrestrial and marine pollen signals in and off western Iberia shows that marine pollen assemblages give an integrated image of the regional vegetation colonising the adjacent continent. Present-day Mediterranean and Atlantic forest communities of Iberia are well discriminated by south and north marine pollen spectra, respectively. Results from Total Pollen Concentration together with recognized conceptual models of fine particle dynamics in the Iberian margin have allowed us to establish the present-day pattern of pollen dispersion in this region.
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Papers by Stephanie Desprat