Solène Pourtout

Doctoral / Post-doctoral researcher

THESIS SUBJECT

Past changes in Atlantic Ocean circulation at intermediate water depths from micropaleontological and geochemical proxies since the last glacial maximum

THESIS SUMMARY

Ocean circulation plays a fundamental role in the redistribution of heat, nutrients and salt throughout the global ocean, thus exerting a major influence on climate regulation. Most of the paleoceanographic work of the last decades has made it possible to find out about the variations in the production of the North Atlantic Deep Water (NADW), highlighting in particular the reduction (during the Last Glacial Maximum, LGM) or even the total stop (during the Younger Dryas YD or the Heinrich 1 H1 event) of NADW production, offset by significant changes in intermediate and deep water flows from the Southern Hemisphere. However, the role of intermediate water bodies during these events remains to be documented and is very controversial. Indeed, some studies have highlighted the increase in the extension of Antarctic Intermediate Water (AAIW) in all ocean basins during the cold events recorded in the North Atlantic while other studies suggest the absence of contribution from these water masses.

This research project therefore aims to 1) better understand the relationships between variations in ocean circulation in the North Atlantic and the Southern Ocean, 2) to characterize the physical and chemical properties of water masses, 3 ) to reconstitute the extension of the AAIW towards the North, 4) to better constrain the variations of source and dynamics of the intermediate water masses and finally, 5) to document the impact of these changes on the global carbon cycle during the last glacial-interglacial termination (termination I). To do this, we are going to work on two sedimentary cores, the first in the north of the Porcupine Basin and the second at the level of the Iberian margin in the south of Portugal. On these two sediment cores, we are going to combine the micropaleontological and geochemical study, in particular by the study of benthic foraminifera assemblages, which are sensitive to variations in the geochemistry of water masses and sediment with complementary geochemical tracers such as elementary ratios (Mg / Ca, Cd / Ca, Sr / ca…), stable isotopes (δ18O oxygen and δ13C carbon), radiocarbon (14C) and neodymium (εNd).

SUPERVISORS

Thesis supervisor : Christophe Colin (GEOPS, Université Paris-Saclay, France)

Thesis co-supervisor : Sophie Sépulcre (GEOPS, Université Paris-Saclay, France)

FUNDING

MESRI (Université Pars-Saclay)