Papers by Marie-alexandrine Sicre
We investigate the low frequency variability of the Atlantic subpolar and subtropical gyres over ... more We investigate the low frequency variability of the Atlantic subpolar and subtropical gyres over the last millennium. First, a compilation of the several recent proxy recontructions (e.g. Sicre et al. 2008, Richter et al. 2009 for the subpolar gyre, Mc Gregor et al. 2007 and unpublished data from Sicre et al. in the subtropical gyre) will allow to assess the
ABSTRACT The recent rapid decline in Arctic sea ice cover has increased the need to improve the a... more ABSTRACT The recent rapid decline in Arctic sea ice cover has increased the need to improve the accuracy of the sea ice component in climate models and to provide detailed long-term sea ice concentration records, which are only available via proxy data. Recently, the highly branched isoprenoid IP25, identified in marine sediments underlying seasonal sea ice, has emerged as a potential sea ice specific proxy for past sea ice cover. We tested the reliability of this biomarker as a sea ice proxy against observational sea ice data (sea ice concentrations from the global HadISST1 database) and against a more established sea ice proxy (sea ice diatom abundance in sediments) in the South-West (SW) Labrador Sea. Furthermore, our study location at the southern margin of Arctic sea ice drift provided a new environmental setting in which to further test the novel PIP25 index. Our two study sites are located North-East (NE) and South-East (SE) of Newfoundland where box cores covering the last ca 100-150 years were collected. IP25 concentrations are nearly an order of magnitude higher and sea ice diatoms more abundant in sediments from NE of Newfoundland, where sea ice prevails 2-4 months per year compared to the sediments SE of Newfoundland, where conditions are generally ice-free year round. The IP25 fluxes NE of Newfoundland agree well with multi-decadal North Atlantic Oscillation (NAO) trends in the study area, which in previous studies have been shown to affect the climatic and sea ice conditions in the region. When assessed against observational sea ice data, IP25 appears to be a more sensitive indicator of sea ice variability in this setting compared to sea ice diatoms and proved to be a robust and reliable proxy for reconstructing low-frequency variability in past sea ice concentrations. The PIP25 index results clearly differ from the observed sea ice data underlining that caution needs to be exercised when using the index in different environmental settings.
A high resolution account of Icelandic sea ice over the last millennium has been constructed usin... more A high resolution account of Icelandic sea ice over the last millennium has been constructed using a novel proxy based on the presence in sediments of a biomarker (IP25) produced by sea ice algae. Comparison with historical sea ice records demonstrates a strong correlation between documented sea ice occurrences and the IP25 proxy. An excellent agreement is also observed between the IP25 record and a diatom-based sea surface temperature reconstruction obtained from the same core and the Crowley and Lowery Northern Hemisphere temperature reconstruction. Using this approach, we provide new historical sea ice data for periods where records are scarce or absent and evidence for abrupt changes to sea ice and/or climate conditions around Iceland during the Little Ice Age.
La Météorologie, 2015
Déterminer les causes à l'origine de l'optimum médiéval chaud au début du dernier millénaire et d... more Déterminer les causes à l'origine de l'optimum médiéval chaud au début du dernier millénaire et de la période froide qui lui a succédé est un véritable défi. La comparaison des températures reconstruites aux résultats des nouvelles simulations numériques à la base du 5 e rapport du Giec révèle le rôle prépondérant du volcanisme avant le XX e siècle. Des incertitudes entourent néanmoins ces résultats. Les estimations des variations du forçage solaire et les processus par lesquels l'activité du Soleil peut agir sur le climat restent insuffisamment contraints. La signature spatiale des anomalies climatiques reconstruites suggère également l'influence des variations internes du climat via les variations lentes de la circulation océanique de grande échelle.
Geochemistry Geophysics Geosystems, 2002
This study assesses the relationship to salinity and temperature of the levels of the tetra-unsat... more This study assesses the relationship to salinity and temperature of the levels of the tetra-unsaturated 37-carbon methyl alkenone (C37:4) in the surface ocean. UK′37, a measure of the relative abundances of the C37:2 and the C37:3 alkenones, has a well constrained linear relationship to temperature in the open ocean [Prahl and Wakeham, 1987] and is a well-established technique for estimating
Geophysical Research Letters, 2000
Two sediment cores were investigated to study the regional climatic variability of the NW African... more Two sediment cores were investigated to study the regional climatic variability of the NW African upwelling over the late Quaternary. Biomarker data and Sea Surface Temperatures (SSTs) predicted from alkenones at 25°N and 21°N exhibited distinct features. The amplitude of the last deglaciation was estimated to 4.5°C at 25°N and 2-2.5°C at 21°N. At 25°N, terrestrial and marine glacial inputs
We present preliminary composite multi-decadal resolution summer (May-October) sea surface temper... more We present preliminary composite multi-decadal resolution summer (May-October) sea surface temperature (SST) reconstructions for the North Atlantic region back to 1255 AD. The composite reconstructions are based on SST records from across the region, derived from a mixture of marine based proxies (diatoms, alkenones, oxygen isotopes and Mg/Ca ratios from planktonic and benthic foraminifera and shell increment widths of Arctica
Ocean variability at decadal,time-scales remains poorly described partly because of the scarcity ... more Ocean variability at decadal,time-scales remains poorly described partly because of the scarcity ofhigh temporal resolution marine records. Here, we present a reconstruction of Sea Surface Temperatures (SSTs) over the past two millennia at unprecedented, temporal ,resolution (2 to 5 years), from a marine core located off North Iceland. Alkenone paleothermometry was used to infer SST variability, and tephrochronology to
Organic Geochemistry, 2001
Molecular statigraphic records of core SU94-11K (21°N, 18°W, 1200 m water depth) were reconstruct... more Molecular statigraphic records of core SU94-11K (21°N, 18°W, 1200 m water depth) were reconstructed for organic carbon (OC), carbonates, alkenones, n-alkanols and sterols over the last 70 ky to study past changes of production and paleoceanographic conditions in the coastal upwelling of Northwest Africa. UK′37-derived sea surface temperatures (SST) show a 2.5 °C warming during the last deglaciation. Surprisingly, they also
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1999
Decadal-scale SST changes were reconstructed over the last millennium from two marine cores, MD99... more Decadal-scale SST changes were reconstructed over the last millennium from two marine cores, MD99-2275 and RAPiD-21-3K, respectively located North and South of Iceland, along the path of the MOC (Meridional Overturning Circulation) to improve our undertanding on the role of this critical region in the global climate system. SSTs during the MCA (Medieval Climatic Anomaly) in both records show similar
Quaternary Science Reviews, 2008
Marine paleo-records acquired at high temporal resolution provide critical data for testing numer... more Marine paleo-records acquired at high temporal resolution provide critical data for testing numerical climate models and help to understand processes underlying ocean variability. This study presents a unique 4500-year reconstruction of sea surface temperature (SST) obtained from alkenones in the North Atlantic Polar Front area off North Iceland, at an average temporal resolution of 4-5 years. Spectral analysis of this signal shows dominant multidecadal oscillations which occurred with a stronger amplitude between 2500 and 4200 years BP, hand in hand with fluctuations of bottom currents indicated by paleomagnetic proxies. Contemporaneous large excursions of the Inter-tropical Convergence Zone (ITCZ) are also recorded by the distant Cariaco titanium time series, suggesting a link with low latitude Atlantic climate. We speculate that the oscillations reflect changes of the Meridional Overturning Circulation (MOC) induced by increased ENSO activity.
Organic Geochemistry, 1998
AbstractÐHydrocarbons, sterols and alkenones were analyzed in samples collected from a 10 month s... more AbstractÐHydrocarbons, sterols and alkenones were analyzed in samples collected from a 10 month sediment trap time series deployed in the Indian Ocean sector of the Southern Ocean. Fluxes and within-class distributions varied seasonally. During higher mass and organic carbon (OC)¯ux periods, which occurred in austral summer and fall, fresh marine inputs were predominant. Vertical¯uxes were most intense in January, but limited to one week in duration. They were, however, low compared with other oceanic regions. In contrast, low mass and OC¯ux periods were characterized by a strong unresolved complex mixture (UCM) in the hydrocarbon fraction and a high proportion of stanols as a result of zooplanktonic grazing. Terrigenous inputs were not detectable. The alkenone compositions were consistent with previous data on suspended particles from Antarctic waters. However, U 37 K' values diverged from the linear and exponential ®ts established by Sikes, E. L. and Volkman, J. K. Calibration of alkenone unsaturation ratios (U 37 K' ) for paleotemperature estimation in cold polar waters. Geochimica et Cosmochimica Acta, 1993, in the low temperature range. The seasonal pattern of alkenone production implied that IPT (integrated production temperature) is likely to be strongly imprinted by austral summer and fall SST (sea surface temperature). #
Organic Geochemistry, 2000
Terrigenous and marine biomarkers were investigated in a core o Northwest Africa in the Northeast... more Terrigenous and marine biomarkers were investigated in a core o Northwest Africa in the Northeast Atlantic (25 N, 16 W, 1445 m depth) to assess changes in the sedimentation pattern of organic carbon (OC) over the last 150 kyears. Alkenone derived temperatures recorded a warming of 4.5 C during the last deglaciation. n-Alkanol Mass Accumulation Rates (MAR)¯uctuated in parallel with Northeast Trade Winds (NETW) intensity. OC and sterol MAR both increased during glacial times indicating enhanced fertility of the ocean in response to intensi®ed NETW. Alkenone/OC ratios were higher by a factor of two over stages 4±6 than stages 1±3 thus re¯ecting distinct coccolithophorid inputs. This transition coincides with a major change of alkenone producers inferred from coccolith counts. #
Marine Geology, 2004
A high-resolution study of clay mineralogy and major element geochemistry has been conducted on h... more A high-resolution study of clay mineralogy and major element geochemistry has been conducted on high sedimentation rate cores (MD01-2393 and MD97-2150) collected off the Mekong River mouth in the southwestern South China Sea in order to reconstruct the erosional and weathering history of the Mekong Basin. The chronology is based upon planktonic foraminiferal oxygen isotope records combined with carbonate stratigraphy.
Marine Chemistry, 2008
A C 25 highly branched isoprenoid (HBI) monoene hydrocarbon, designated IP 25 , has been proposed... more A C 25 highly branched isoprenoid (HBI) monoene hydrocarbon, designated IP 25 , has been proposed previously to originate from diatoms living in Arctic sea ice, while the presence of IP 25 in sediments has been suggested to be a proxy for the occurrence of former Arctic sea ice. Here, we show that the 13 C isotopic composition of IP 25 in sea ice, in sediment trap material collected under sea ice, and in high latitude northern sediments, is distinctive (isotopically 'heavy') and distinguishable from that of organic matter of planktonic or terrigenous origin. Mean δ 13 C values for IP 25 were − 22.3 ± 0.4‰ (sea ice), −19.6 ± 1.1‰ (sediment traps) and −19.3 ± 2.3‰ (sediments). These measurements, therefore, support further the proposed use of IP 25 as an Arctic sea ice proxy.
Geochemistry, Geophysics, Geosystems, 2006
1] In this paper, we compile the current surface seawater C 37 alkenone unsaturation (U 37 K 0 ) ... more 1] In this paper, we compile the current surface seawater C 37 alkenone unsaturation (U 37 K 0 ) measurements (n = 629, À1 to 30°C temperature range) to derive a global, field-based calibration of U 37 K 0 with alkenone production temperature. A single nonlinear ''global'' surface water calibration of U 37 K 0 accurately predicts alkenone production temperatures over the diversity of modern-day oceanic environments and alkenonesynthesizing populations (T = À0.957 + 54.293(U 37 K 0 ) À 52.894(U 37 K 0 ) 2 + 28.321(U 37 K 0 ) 3 , r 2 = 0.97, n = 567). The mean standard error of estimation is 1.2°C with insignificant bias in estimated production temperature among the different ocean regions sampled. An exception to these trends is regions characterized by strong lateral advection and extreme productivity and temperature gradients (e.g., the Brazil-Malvinas Confluence). In contrast to the surface water data, the calibration of U 37 K 0 in surface sediments with G 3
Geochemistry, Geophysics, Geosystems, 2000
... Woods Hole Oceanographic Institution, 360, Woods Hole Road, Woods Hole, Massachusetts 02543-1... more ... Woods Hole Oceanographic Institution, 360, Woods Hole Road, Woods Hole, Massachusetts 02543-1543. H. Rodger Harvey. Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, PO Box 38, Solomons, Maryland 20688. Miguel Goñi. ...
Earth and Planetary Science Letters, 2008
Ocean variability at decadal time-scales remains poorly described partly because of the scarcity ... more Ocean variability at decadal time-scales remains poorly described partly because of the scarcity of high temporal resolution marine records. Here, we present a reconstruction of Sea Surface Temperatures (SSTs) over the past two millennia at unprecedented temporal resolution (2 to 5 years), from a marine core located off North Iceland. Alkenone paleothermometry was used to infer SST variability, and tephrochronology to built the age model. Spectral analyses of the SST signal indicate intermittent 20-25 year oscillations, with periods of strong and weak power, that are likely reflecting the ocean response to wind forcing, presumably the North Atlantic Oscillation (NAO). Warmer SSTs and paleo-magnetic proxy data, between 1000 and 1350 year A.D., overlapping the Medieval Warm Period (MWP), suggest enhanced heat transport across the Denmark Strait by the North Icelandic Irminger Current (NIIC) This is in contrast with the subsequent period, which includes the Little Ice Age (LIA), showing continuous cooling towards the 20th century. Reduced NIIC flow through the Denmark Strait likely resulting from higher freshwater and sea ice export from the Arctic would account for the observed colder conditions.
Earth and Planetary Science Letters, 2008
A high resolution account of Icelandic sea ice over the last millennium has been constructed usin... more A high resolution account of Icelandic sea ice over the last millennium has been constructed using a novel proxy based on the presence in sediments of a biomarker (IP25) produced by sea ice algae. Comparison with historical sea ice records demonstrates a strong correlation between documented sea ice occurrences and the IP25 proxy. An excellent agreement is also observed between the IP25 record and a diatom-based sea surface temperature reconstruction obtained from the same core and the Crowley and Lowery Northern Hemisphere temperature reconstruction. Using this approach, we provide new historical sea ice data for periods where records are scarce or absent and evidence for abrupt changes to sea ice and/or climate conditions around Iceland during the Little Ice Age.
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Papers by Marie-alexandrine Sicre