Periodic Reporting for period 1 - INDEXCLIMA (Indian-Atlantic interocean exchange as modulator of global climate)
Reporting period: 2019-10-01 to 2021-09-30
The overall objectives of the project were:
(1) To reconstruct how the Atlantic deep water and southern-sourced deep water flowing into the Indian Ocean varied during the last 630,000 years, and evaluate how deep-water carbon storage varied with time and space.
(2) To analyse the relationship of Indian-Atlantic interocean exchange between surface and deep waters in order to evaluate the impact of the Indian surface waters entering Atlantic Ocean via the Agulhas rings to the Atlantic meridional overturning circulation under different climate conditions.
WP 1: Application of a new automated prototype machine to evaluate the preservation state of biogenic calcite
The fellow performed the analysis of the preservation of planktic foraminiferal shells distinguishing fragments of shells from complete shells using a prototype machine. This device is able to automatically recognise fragments and whole shells thanks to multiple images processed by artificial intelligence. Higher abundance of fragments, indicating possible dissolution of carbonate shells, occurred during warm interglacial periods. In addition, the fellow assessed visually the preservation of foraminiferal shells using a binocular magnifier. This helped to select only well-preserved foraminifera for chemical analyses. The fellow attended virtually a conference to present the first project results.
WP 2: Reconstruction of the Indian surface waters entering the Atlantic Ocean
For reconstructing the variation of Indian surface waters flowing into the Atlantic Ocean, a group of 5 species of planktic foraminifera were used. These species inhabit warm surface waters in the Indian Ocean and are found in Agulhas rings in the southeastern (SE) Atlantic Ocean. This group of species increased at the end of glacial periods, when Agulhas rings were estimated to be more abundant. Furthermore, the planktic foraminiferal species Globoconella inflata was used as proxy for temperate waters. Decreases of this species at the end of glacial periods indicated lower arrival of temperate waters from below 42°S. Based on these data, the most interesting time intervals over the last 630,000 years were selected.
WP 3: Atlantic deep-water circulation flowing into the Indian Ocean
To assess changes in Atlantic deep-water masses entering the southwestern (SW) Indian Ocean, Neodymium (Nd) isotopic composition and carbon isotopic composition were analysed. Nd isotopic composition is a tracer of water mass provenance while benthic foraminiferal carbon isotopic ratio is a sensitive tracer to water ventilation. Combination of the two geochemical tools revealed (i) decreases in northern-source Atlantic water contribution to the deep Indian water during glacial periods and (ii) storage of respired carbon that was enhanced in glacial waters below 2700 m. The new results suggest spatial extension deep-water with high carbon content to the SW Indian Ocean at least as far as 33ºS. The fellow attended an online international conference to present the final project results.
WP 4: Integration of project results to reconstruct influence of surface and deep Indian-Atlantic water mass exchange on global ocean circulation and climate
All project results were integrated and compared with available results to reconstruct spatiotemporal changes in surface and deep Indian-Atlantic water mass exchange. Two scientific articles will be submitted and published as open access articles with all data will be accessible (e.g. Pangaea data depository). The first article analyses the CO2 storage capacity of glacial Atlantic deep waters entering the SW Indian Ocean. The second article investigates the Indian-Atlantic subsurface- and deep-water mass exchange at the end of glacial periods. These two articles include the exploitable project results: planktic foraminiferal warm species and G. inflata abundances, fragmentation index data, foraminiferal Nd isotopic data, and benthic foraminiferal carbon isotope data.
The fellow also participated in an outreach activity (Science Festival) for Primary School students in France. He also supervised several students at the host institution, helping them to identify foraminiferal species. He performed scientific and administrative tasks related to project management, including budget expenses and organisation of meetings with supervisor and collaborators.