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When eastern India oscillated between desert versus savannah‐dominated vegetation

Publication . Zorzi, Coralie; Desprat, Stéphanie; Clément, Charlotte; Thirumalai, Kaustubh; Oliveira, Dulce; Anupama, Krishnamurthy; Prasad, Srinivasan; Martinez, Philippe

During the last glacial period, the tropical hydrological cycle exhibited large variability across orbital and millennial timescales. However, the response of the Indian summer monsoon (ISM), its related impact on terrestrial ecosystems, and associated forcing mechanisms remain controversial. Here we present a marine record of pollen-inferred vegetation changes suggesting that eastern India shifted from woody-savanna mosaics during Marine Isotopic Stage 3 to grasslands during the Last Glacial Maximum resulting from large-scale drying. Our data shows that ISM maximum is in phase with obliquity and precession maxima suggesting a dominant role of the Indian Ocean interhemispheric temperature gradient on glacial ISM variability. Persistent and abrupt dryland expansions of varying magnitude suggest rapid-scale onset of aridity during Heinrich Stadial events and during the Toba eruption. We propose that the amplitude of ISM drought events are initiated by high latitude and volcanic forcings, although modulated by precession.

2022Journal article

Open access

Ocean productivity in the Gulf of Cadiz over the last 50 kyr

Publication . Penaud, A.; Eynaud, F.; Etourneau, J.; Bonnin, J.; Vernal, A.; Zaragosi, S.; Kim, J.-H.; Oliveira, Dulce; Waelbroeck, C.

Reconstructions of ocean primary productivity (PP) help to explain past and present biogeochemical cycles and climate changes in the oceans. We document PP variations over the last 50 kyr in a currently oligotrophic subtropical region, the Gulf of Cadiz. Data combine refined results from previous investigations on dinocyst assemblages, alkenones, and stable isotopes ( 18O, 13C) in planktonic (Globigerina bulloides) and endobenthic (Uvigerina mediterranea) foraminifera from cores MD04-2805 CQ and MD99-2339, with new isotopic measurements on epibenthic (Cibicides pachyderma–Cibicidoides wuellerstorfi) foraminifera and dinocyst-based estimates of PP using the new n = 1,968 modern database. We constrain PP variations and export production by integrating qualitative information from bio-indicators with dinocyst-based quantitative reconstructions such as PP and seasonal sea-surface temperature and information about remineralization from the benthic  13C (difference between epi- and endo-benthic foraminiferal  13C signatures). This study also includes new information on alkenone-based SST and total organic carbon which provides insights into the relationship between past regional hydrological activity and PP regime change. We show that PP, carbon export, and remineralization were generally high in the NE subtropical Atlantic Ocean during the last glacial period and that the Last Glacial Maximum (LGM) had lower  13C than the Heinrich Stadials with sustained high PP, likely allowing enhanced carbon sequestration. We link these PP periods to the dynamics of upwelling, active almost year-round during stadials, but restricted to spring-summer during interstadials and LGM, like today. During interstadials, nutrient advection through freshwater inputs during autumn–winter needs also to be considered to fully understand PP regimes.

2022-02Journal article

Open access