During MD218 CROTALE expedition, four CALYPSO piston cores and three gravity CASQ cores were retrieved. Three piston cores, ranging from ~40 m to ~70 m long, possibly cover the last ~1.5 to ~5 million years. However, on-board measurements did not allow to develop a robust chronological framework for these long cores, which is obviously essential to replace all analyses in a paleoclimatic context. The present demand therefore focuses on performing key analyses to obtain a chronological framework for these three cores as a basis for future large-scale national and international projects. Analyses will be: – 20 cm resolution d18O and d13C measurements on foraminifera to evidence glacial-interglacial cyles. – Paleomagnetism analyses to evidence glacial-interglacial cycles and excursions/reversals. – Centimetric measurements of sediment elemental composition through XRF core-scanner to evidence glacial-interglacial cycles and rapid changes. – Biostratigraphy based on coccolith ACME zones and diatom LAD/FAD. Diatom census counts in samples older than 0.35 Ma will also ensure applicability of diatom-based transfer functions to reconstruct sea-surface temperatures when extinct diatoms were present. Sea-surface temperatures will also be used to refine chronologies.
MD225 – ACCLIMATE-2 coring cruise took place on board the R/V Marion Dufresne between February 9th and March 1st 2020, sailing from Durban to Durban (South Africa) in the Atlantic sector of the Southern Ocean. The objective of the cruise was to retrieve high sedimentation rate marine sediments from different latitudes and water depths in the South-East Atlantic in order to fill a critical gap in paleoceanographic data in this area. Sediment cores collected from different water depths will provide the necessary material to reconstruct the evolution of the water mass vertical structure in this region over the last 40 thousand years (ky) and beyond. Coring sites are distributed between 33 and 53°S and between ~2000 and 4600 m water depth This coring cruise is a follow-up of the ACCLIMATE cruise which took place in March 2016 in the framework of the European Research Council (ERC) project ACCLIMATE (“Elucidating the Causes and Effects of Atlantic Circulation Changes through Model-Data Integration”). Because of bad weather conditions due to the lateness of the cruise that year, 7 coring sites out of the 12 sites initially planned had to be abandoned; these were the sites revisited in 2020. The project’s purpose is to elucidate the links between Atlantic Ocean circulation changes and climatic changes. Indeed, rapid changes in ocean circulation and climate have been observed in marine sediment and ice cores, notably over the last 40 ky, highlighting the non-linear character of the climate system and underlining the possibility of rapid climate shifts in response to anthropogenic greenhouse gas forcing. To date, these rapid changes in climate and ocean circulation are still not fully explained. The quality of the recovered cores, specially of the long Calypso ones, is outstanding. After analysis of the first onboard data, it was shown that not only they contain exceptional records of the last 40 ky, but, thanks to their length, they are also unique archives of the last few glacial-interglacial cycles. The research plan presented here will focus on defining a robust chronology of the sediment sequences, analyzing sediment composition at high resolution, and producing medium/low resolution isotopic records that will provide information on deep water mass variations. For that, we request funding to produce preliminary age scales and the first low resolution reconstructions of water mass changes.