Changes in planktic and benthic foraminifer assemblages in the Gulf of Lions, off south France: Response to climate and sea level change from MIS 6 to MIS 11

Abstract

[1] A multidisciplinary study involving micropaleontological and geochemical tools was carried out in borehole PRGL1 (Promess 1), with the aim of reconstructing the impact of climate change and sea level variation between 133 ka and 406 ka in the upper slope of the Gulf of Lions. We used factor analysis to obtain three main benthic assemblages related to eutrophic, mesotrophic, and oxygenated environments; planktic foraminifers were grouped as warm-water and cold-turbulent species. These results were compared with records of CaCO 3 and major and trace elements (Al, Ca, K, Sr) as well as the C/N ratio of organic matter. Power and cross-spectral analysis showed a straightforward relationship between precession minima and thermal stratification of the water column as well as the occurrence of eutrophic bottom conditions during lowstand periods and mesotrophic environments at times of highstand. These eutrophic-mesotrophic oscillations, usually driven by global eustatic change, also involved regional variations in CaCO 3 source to this environment. During periods of precession maxima, enhancement of northwesterly winds increased primary productivity by mixing, enhancing the percentage of cold-turbulent species in the water column and the proportion of oxygenated benthic species on the bottom. During interglacial stages, these events were recorded by lower biogenic carbonate at the expense of higher silicate-related components most likely due to a higher supply from Pyrenees rivers. The record of oxygenated benthic species can be a good proxy to monitor past changes in Winter Intermediate Water dynamics driven by northwesterly winds.

Quantifying Biogenic Versus Detrital Carbonates on Marine Shelf: An Isotopic Approach

“…During glacial times, we observe a greater CaCO 3 proportion of what is unexpected considering the low carbonate productivity observed in the western Mediterranean Sea (Hoogakker et al, 2004;Toucanne et al, 2015). Interestingly, this increase in carbonate content is concomitant with a higher detrital flux (Cortina et al, 2013(Cortina et al, , 2016Pasquier et al, 2017Pasquier et al, , 2018; as the rise around 155 ka is synchronous with an extensive melting episode of Alpine ice-caps and local glaciers (Toucanne et al, 2009;Bickel et al, 2015 and reference therein), (Figure 2). This suggests a significant increase of detrital carbonates exported during glacial conditions.…”

The response of SST to insolation and ice sheet variability from MIS 3 to MIS 11 in the northwestern Mediterranean Sea (Gulf of Lions)

“…This pattern contrast with low North Atlantic Deep Water (NADW) production, being this anticorrelation broken at times of Heinrich events [ Sierro et al ., ]. Although WMDW formation does not take place at the location of PRGL1, our core site is in the path of northwesterly winds and records satisfactorily its intensity from MIS 6 to MIS 11 [ Cortina et al ., ].…”

“…The enhancement of northwesterly winds has been recorded during glacial substages of MIS 7, MIS 9, and MIS 11 [ Cortina et al ., ] when the NADW weakened. However, the high sensitivity of SST in the GL to northern ice sheet inception in comparison with southern locations could indicate an increase of WMDW production at times of warmer events in the Mediterranean basin, resulting in coupled WMDW and NADW productions between the colder and the warmer episodes during interglacials.…”

“…At present, sea surface temperature (SST) distribution and surface circulation are strongly affected by cold northwesterly winds [Pinardi and Masetti, 2000]. Some micropaleontological studies at PRGL1 [Cortina et al, 2011[Cortina et al, , 2013 recorded an intensification of these winds during cold periods, causing increased mixing of the water column. Kuhlemann et al [2008] produced for the Last Glacial Maximum (LGM) a Mediterranean synthesis of proxy data from sea surface to alpine latitudes.…”

Climate-driven changes in sedimentation rate influence phosphorus burial along continental margins of the northwestern Mediterranean

“…3E, 3F, 3G). Moreover, weak correlations were found between previous published [Al] data (Cortina et al, 2013) and % Non-recovered P (R 2 <0.2). Titanium is preferentially concentrated in the coarser sediment fractions (Spears and Kanaris-Sotiriou, 1976) being an indicator of average grain size.…”