Catherine Kissel’s research while affiliated with University of Paris-Saclay and other places

Chilean Patagonia is confronted with several geohazards due to its tectonic setting, i.e., the presence of a subduction zone and numerous fault zones, e.g., the Liquiñe-Ofqui Fault Zone (LOFZ). This region has therefore been the subject of numerous paleoseismological studies. However, this study reveals that the seismic hazard is not limited to these large tectonic structures by identifying past fault activity near Coyhaique in Aysén Region. Mass-wasting deposits in Lago Pollux, a lake located ca. 15 km SW of this region's capital, were identified through analysis of reflection-seismic data and were linked to a simultaneous event recorded in nearby Lago Castor. Furthermore, a coeval ∼50-year-long catchment response was identified in Aysén Fjord based on the multiproxy analysis of a portion of a sediment core. Assuming that this widely recognized event was triggered by an earthquake, ground-motion modeling was applied to derive the most likely magnitude and source fault. The model showed that an earthquake rupture along a local fault, in the vicinity of Lago Pollux and Lago Castor, with a magnitude of 5.6–6.8, is the most likely scenario.

Sea ice conditions in the eastern Fram Strait between 40 and 36.5 ka b2k (thousand years before the year 2000) are reconstructed in detail, based on biomarker analyses. Following extensive sea ice conditions around the Greenland Interstadial 9/Greenland Stadial 9 transition at 39.9 ka b2k, repeated polynya activity marked Greenland Stadial 9 in the eastern Fram Strait. Nearly perennial sea ice was observed around the Greenland Stadial 9/Greenland Interstadial 8 transition at 38.22 ka b2k, followed by a gradual establishment of seasonal sea ice cover over the research area during Greenland Interstadial 8. Previous studies highlighted sea ice retreat in the southeastern Nordic Seas as a driver of abrupt Greenland Stadial to Interstadial climate change. We document intervals with less sea ice in the eastern Fram Strait during Greenland Stadial 9 and Interstadial 8 than previously suggested. By mapping the variable sea ice extent during Greenland Stadial 9 and Interstadial 8, further constraints are detected that may help define the role of the Nordic Seas sea ice cover in driving abrupt climate change during glacial times.

Chilean Patagonia is confronted with several geohazards due to its tectonic setting, i.e., the presence of a subduction zone and numerous fault zones (e.g. the Liquiñe-Ofqui Fault Zone). This region has therefore been the subject of numerous paleoseismological studies. However, this study reveals that the seismic hazard is not limited to these large tectonic structures by identifying past fault activity near Coyhaique in the Aysén Region. Mass wasting deposits in Lago Pollux, a lake located ca. 15 km SW of this region’s capital, were identified through analysis of reflection-seismic data and was linked to a simultaneous event recorded in nearby Lago Castor. Furthermore, a coeval ~50 year-long catchment response was identified in Aysén Fjord based on the multiproxy analysis of a portion of a sediment core. Assuming that this widely recognized event was triggered by an earthquake, ground-motion modelling was applied to derive the most likely magnitude and source fault. The model showed that an earthquake rupture along a local fault, in the vicinity of Lago Pollux and Lago Castor, with a magnitude of 5.6–6.8, is the most likely scenario.

The Southern Ocean (SO) plays a fundamental role in global climate due to the presence of the intense eastward‐flowing Antarctic Circumpolar Current (ACC), one of the most important ocean current systems. The configuration of the frontal systems of the ACC is controlled by the orbital‐ and millennial‐scale variations of the Southern Hemisphere westerly winds (SHWW) and the SO upwelling. However, the reconstruction of paleoclimate and paleocurrent in the SO remains controversial possibly because of the complex interpretation of paleo‐proxies and the regional variations. Here, we present results from rock magnetic measurements and electron microscopic analyses on marine core MD11‐3353 over the past 150 Kyr, which is located in the Polar Front Zone, west of the Kerguelen Plateau. Our data sets indicate that magnetic mineral assemblages in the core are dominated by detrital magnetic minerals mixed with biogenic magnetic minerals (i.e., magnetofossils formed by magnetotactic bacteria) during the interglacial periods. Changes in the detrital magnetic mineral content indicate a strong modulation of the ACC intensity and the SHWW stress at the orbital scale over the last climatic cycle with an enhanced activity during the glacial periods. The increase in magnetofossils content during the interglacial periods indicates an enhanced nutrient supply from the SO upwelling resulting from the southward migration of the Antarctic Polar Front. Our results suggest that the variations of concentration and assemblage of magnetic minerals can be used as faithful proxies for reconstructing ocean circulation and upwelling changes in the South Indian Ocean over the past 150 Kyr.

Megaturbidites are commonly used to reconstruct the seismic history (palaeoseismology) of areas where large earthquakes occur. However, the depositional mechanisms and sedimentary characteristics of these deposits are not yet fully understood. This study unravels the sequence of sediment deposition that occurred in Lake Lucerne (Vitznau Basin) following the 1601 CE earthquake in central Switzerland. During this event, slope failures were triggered, generating mass flows and turbidity currents that led to the formation of mass‐transport deposits and a megaturbidite. These deposits are sampled in 28 sediment cores, which are examined with X‐ray computed tomography scans (medical and μCT), grain‐size analysis and natural remanent magnetisation. This suite of analyses allows a detailed reconstruction of turbidite stacking and amalgamation in the centre of the basin, followed by settling of finer sediments influenced by a lake seiche. Initial deposition of mass‐transport deposits is followed by sandy turbidites reaching the depocentre. Some of these turbidite sands can be linked to their source areas, and evidence is found of some turbidites being overridden by mass flows in the peripheral parts of the megaturbidite deposit. Hereafter, sedimentation becomes controlled by seiche‐induced currents, which rework fine sediments upon deposition, leading to subtle grain‐size variations at the base of the seiche‐influenced sub‐unit and a ponded geometry of the megaturbidite. As the seiche movement dampens, a relatively muddy, homogeneous sub‐unit is deposited that drapes the basin plain. Overall, this study provides the first highly detailed sedimentological analysis of megaturbidite deposition in a lake, demonstrating the distinct sedimentological imprint of lake seiching and turbidite amalgamation/stacking. This will improve the recognition and interpretation of earthquake‐induced megaturbidites in other lake records or isolated basins, and demonstrates the value of using (μ)CT scans in combination with traditional sedimentological parameters to reconstruct the depositional processes of megaturbidites.

Reconstructions of past changes in deep‐sea current intensities are needed to understand ocean‐climate interactions in the past. The mean size of the sortable silt fraction (10–63 μm, SS‾ $\overline{SS}$) is one of the most used proxies in this domain. However, in polar and subpolar environments under relatively low flow speed conditions, the presence of Ice‐Rafted Detritus (IRD) may alter the SS‾ $\overline{SS}$ record and thus bias the interpretation of paleo‐current strength changes. In this paper, we examine the influence of IRD on the SS‾ $\overline{SS}$ record of three sedimentary cores from the subpolar North Atlantic and the Antarctic margin. The influence of unsorted IRD on SS‾ $\overline{SS}$ records is clearly established. To remove this IRD influence on grain‐size distributions (GSDs), we propose a new method based on End‐Member Analysis approach, and for which a MATLAB script is made available. This method characterizes the GSD of the unsorted IRD input, allowing it to be isolated and discarded, and the current sensitive SS‾ $\overline{SS}$ variability to be robustly identified. The method therefore allows the recalculation of a modified sediment GSD free of unsorted IRD influence and the construction of modified SS‾ $\overline{SS}$ and sortable silt percentage (the % of the 10–63 μm in the total <63 μm fraction) records. The application of the method to the three studied cores shows that (a) the unsorted IRD component is correctly removed from the grain‐size signal and (b) the new SS‾ $\overline{SS}$ record is consistent with the XRF‐based ln(Zr/Rb) grain‐size proxy.

The Arabian Sea (AS) is one of the most productive oceanic regions in the world due to several monsoon‐related processes that can increase nutrients contents in the euphotic zone. Previous studies of the imprint of oceanic primary productivity (PP) in AS sediments yielded diverse results depending on the studied area and the chosen proxies, with unprecise paleoclimatic interpretations. Here, we provide multi‐decennial PP and coastal upwelling dynamic records off northern Oman over the last 23 Kyr, based on the analysis of coccoliths from sediment core MD00‐2354. Our results have been compared with previous paleoenvironmental records as well as new modeling data to get precise paleoclimatic interpretations. We document higher PP and weaker coastal upwelling during the Last Glacial Maximum relative to the Holocene, and significant millennial‐scale variations over the last deglaciation corresponding to the fluctuations of the Atlantic Meridional Overturning Circulation strength. Higher PP and weaker upwelling are found during the cold stadials, while lower PP and stronger upwelling during the warm interstadial. We propose that the increases of PP were driven by increased bioavailable nutrient content in surface waters under both stronger winter monsoon conditions that strengthened the convective mixing, and higher aeolian inputs. Over the Holocene, stronger upwelling and slightly lower PP are found during the Early‐Mid Holocene, when higher summer insolation triggered stronger summer monsoon. At that time, the lower PP was probably the result of restricted advection of eutrophic summer upwelling seawater under negative wind stress curls and less aeolian inputs.

Assuming that foraminiferal clumped isotope (Δ47) values are independent of seawater salinity and pH, the combination of Mg/Ca, δ¹⁸O and Δ47 values, may in theory allow us to disentangle the temperature, salinity/δ¹⁸Osw and pH signals. Here, we present a new Mg/Ca-Δ47 dataset for modern planktonic foraminifera, from various oceanographic basins and covering a large range of temperatures (from 0.2 to 25.4 °C). These measurements were performed on the same samples and species as the ones used for the foraminiferal Δ47 calibration of Peral et al. (2018), allowing comparison between both Mg/Ca and Δ47 paleothermometers (excluding the two benthic foraminiferal data points). There is a good agreement between these two paleothermometers when the Mg/Ca-temperature is corrected for seawater salinity and pH, suggesting that foraminiferal Δ47 may not be influenced by salinity or pH. However, our results show that Δ47 temperature uncertainties still limit our ability to reconstruct pH and δ¹⁸Osw from the combination of Mg/Ca, δ¹⁸O and Δ47 in a useful manner. We also find that disagreements between Mg/Ca and Δ47 values in G. bulloides persist after correction for vital, salinity and pH effects, suggesting that other process(es) may also influence Mg/Ca in this species. This study also provides an updated I-CDES version of the previously published planktonic and benthic foraminiferal Δ47 calibration of Peral et al. (2018) , covering a range of temperature from -2 to 25.4 °C.

Assuming that foraminiferal clumped isotope (Δ47) values are independent of seawater salinity and pH, the combination of Mg/Ca, δ18O and Δ47 values, may in theory allow us to disentangle the temperature, salinity/δ18Osw and pH signals. Here, we present a new Mg/Ca-Δ47 dataset for modern planktonic foraminifera, from various oceanographic basins and covering a large range of temperatures (from -0.8 to 25 °C). These measurements were performed on the same samples and species as the ones used for the foraminiferal Δ47 calibration of Peral et al. (2018), allowing comparison between both Mg/Ca and Δ47 paleothermometers. There is a good agreement between these two paleothermometers when the Mg/Ca-temperature is corrected for seawater salinity and pH, suggesting that foraminiferal Δ47 shows not relationship to salinity nor pH. Our results show, however, that Δ47 temperature uncertainties still limit our ability to reconstruct accurately enough pH and δ18Osw from the combination of Mg/Ca, δ18O and Δ47. This article also presents an update of the previously published foraminiferal Δ47 calibration (Peral et al., 2018), that can be directly applied to palaeoceanographic studies: Δ47 = 37.0 x 10^3 / T^2 + 0.181.