Holocene North-Atlantic Gyres and Mediterranean Overturning dynamic through Climate Changes – HAMOC

The salinity and heat balance of the North Atlantic region is of paramount importance for the Northern Hemisphere climate and is intimately tied to the northward transport of heat and salt through the gyre and intergyre circulations and the Atlantic Meridional Overturning Circulation (AMOC), as revealed by modern hydrographical observations and model simulations. However, little is known about the long-term and low frequency (centennial to millennial) Atlantic gyres variability and their link to climate as well as to salt and heat contributions from the Mediterranean Sea. Previous studies have shown that sub-millennial variability throughout the last 11,500 years (the Holocene) are modulated by wind forcing and freshwater fluxes affecting the subpolar gyre strength and thus the surface properties of the North Atlantic waters entering the Nordic Seas. During the Holocene, the North Atlantic/European climate, including the Mediterranean area, have undergone significant changes as recorded by sea surface temperatures (SSTs), continental precipitation and air temperature reconstructions. Understanding the causes of climate variability in proxy records requires an integrated approach combining surface and sub-surface ocean properties and continental time series at decadal to centennial time-scales and their comparison with model simulations.
This project aims at producing robust geochemical proxy reconstructions in key regions of the North Atlantic and Mediterranean Sea for the past 11,500 years by using paleoceanographic proxies of SST (d18O and Mg/Ca from foraminifera, alkenones, derived quantification from microfossil assemblages), geochemical water mass tracers (eNd and d13C of foraminiferal tests) as well as novel tracers (eNd, Li/Mg) recorded in precisely dated cold-water corals (U/Th dating). Paleoclimate reconstructions will be evaluated against instrumental data over the 20th century, when possible, using modern corals and sediments collected with box-corers and ROV. To reach these objectives, our strategy will take advantage of the successful developments and scientific partnership of the ANR PICC, IDEGLACE (2005-2009) and NEWTON (2006-2010) previous projects. The HAMOC project will also benefit from the unique sample collections gathered during the past ten years of research on cold-water coral collection from along the eastern European margin and Mediterranean basin (INSU ICE-CTD, projects FP6 HERMES, FP7 HERMIONE, FP7 EPOCA, and FP7 CORALFISH) and interactions with European climate projects such as the FP7 Past4Future that produced numerical simulations and climate reconstructions including the Holocene period. Finally, HAMOC will strongly benefit from new laboratory infrastructure such as cutting edge mass spectrometry techniques (Neptuneplus MC-ICPMS – IDES/LSCE and CEREGE) and recent analytical developments for rapid and precise isotope measurements (eNd) and age determination (U-series and AMS 14C dating) on corals. On the modelling side, the project will benefit from long simulations over the Holocene from the state-of-the-art IPSLCM5A climate model where ocean tracers are implemented.
Broader Impacts: The project will document the relationships between climate and cold-water coral ecosystems in the North Atlantic and Mediterranean Sea. This project will further support the career of young research fellows (PhD students and postdocs) who will develop their scientific skills in an emerging field linking marine geochemistry, oceanography and climatology expertises. The consortium will dedicate a significant effort for public outreach to raise awareness on coral ecosystems and the natural climate variability of the North Atlantic Ocean.