Browsing by Author "Zaragosi, S."
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- Climate variability across the last deglaciation in NW Iberia and its marginPublication . Naughton, F.; Goni, Maria F. Sanchez; Rodrigues, T.; Salgueiro, Emilia; Costas, Susana; Desprat, S.; Duprat, J.; Michel, E.; Rossignol, L.; Zaragosi, S.; Voelker, Antje; Abrantes, FatimaThe direct comparison between marine and terrestrial data from the NW Iberian margin, core MD03-2697, allows us to accurately evaluate, without chronological ambiguity, the vegetation response to North Atlantic climate events across the last deglaciation. Comparison of MD03-2697 data with other marine and terrestrial records from a vast area stretching from the Azores to western (W) France, Iberia and its margin, the W Mediterranean and NW Africa reveals the importance of enhanced winter North Atlantic westerlies episodes in driving a heterogeneous regional climatic signal during particular events of the last deglaciation. Heinrich Stadial 1 (HS1)/Oldest Dryas is a complex event marked by three synchronous main phases (a: extremely cold/relatively wet; b: cool/dry; c: relatively warmer/increasing moisture availability) in regions directly influenced by the North Atlantic while it is characterized by a single phase (cold and dry) in most inland and high altitude areas. Changes in the strength and position of North Atlantic westerlies could explain the variability in moisture during HS1 from W Pyrenees to W Mediterranean. The Bolling-Allerod (B-A) event is marked by a synchronous progressive increase of ocean and atmospheric temperatures and precipitation from the Bolling to the Allerod in W Iberia and W Pyrenees contrasting with the Greenland temperature pattern. Mid-to high latitudes thermal contrast and the gradual strengthening of the Atlantic Meridional Overturning Circulation (AMOC) triggered the continuing enhancement of westerlies, and moisture, along this period.Finally, the Younger Dryas (YD) Stadial is characterized by a land-ocean synchronous returning cold conditions (but not so cold as HS1) and, although dry conditions persisted during this period, extreme winter precipitation occurrences might have affected the most coastal areas of north and central W Iberia and Pyrenees. In contrast, dry conditions persisted during the YD in the western Mediterranean regions. The westerlies migrated further north following the displacement of the Polar Front during the deglaciation precluding the input of moisture in the W Mediterranean region, which persisted very dry during the YD Stadial. (C) 2016 Published by Elsevier Ltd.
- Ocean productivity in the Gulf of Cadiz over the last 50 kyrPublication . 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.