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Percorrer por autor "Waelbroeck, C."

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  • Dansgaard-Oeschger and Heinrich event temperature anomalies in the North Atlantic set by sea ice, frontal position and thermocline structure
    Publication . Pedro, J.B.; Andersson, C.; Vettoretti, G.; Voelker, Antje; Waelbroeck, C.; Dokken, T.M.; Jensen, M.F.; Rasmussen, S.O.; Sessford, E.G.; Jochum, M.; Nisancioglu, K.H.
    We use eighteen timescale-synchronised near-surface temperature reconstructions spanning 10-50 thousand years before present to clarify the regional expression of Dansgaard-Oeschger (D-O) and Heinrich (H) events in the North Atlantic. The North Atlantic Drift region shows D-O temperature variations of ca. 2-5?? with Greenland-like structure. The Western Iberian Margin region also shows Greenland-like structure, but with more pronounced surface cooling between interstadials and Heinrich stadials (ca. 6-9 ??C) than between interstadials and non-Heinrich stadials (ca. 2-3 ??C). The southern Nordic Seas show smaller D-O temperature anomalies (ca. 1-2 ??C) that appear out of phase with Greenland. These spatial patterns are replicated in a new global climate model simulation that features unforced (D-O-like) and freshwater forced (H-like) abrupt climate changes. The model simulations and observations suggest consistently that the spatial expression and amplitude of D-O and H event temperature anomalies are dominated by coupled changes in the Atlantic Meridional Overturning, sea ice extent, polar front position and thermocline structure. ?? 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
    2022Artigo científico Acesso aberto Ver mais
  • 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.
    2022-02Artigo científico Acesso aberto Ver mais