Last Glacial Maximum paleoproductivity and water masses off NW-Africa: Evidence from benthic foraminifera and stable isotopes

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• 作者：A. Eberwein ; A. Mackensen
• 关键词：Last Glacial Maximum ; Paleoproductivity ; NW-Africa ; Water mass ; Stable carbon and oxygen isotopes ; Benthic foraminifera
• 刊名：Marine Micropaleontology
• 出版年：2008
• 期刊代码：58_03778398
• 类别：ear
• 出版时间：April 2008
• 卷：67
• 期：1-2
• 页码：87-103
• 文件大小：835 K

摘要

Last Glacial Maximum (LGM) paleoproductivity, organic carbon (C_org) fluxes, and seasonality was reconstructed from benthic foraminiferal faunas and the stable carbon and oxygen isotopes of foraminiferal calcite. Sediments of the LGM between 23,000 to 19,000 cal-yr BP of sixteen cores from the upwelling region off Morocco between Cape Ghir (31°N) and Cape Yubi (27.5°N) were investigated. Four regions with distinct paleo-C_org fluxes and seasonality were reconstructed based on faunal assemblages and δ¹³C values of Hoeglundina elegans: (1) the Cape Yubi Upwelling Region with high paleoproductivity, high paleo-C_org fluxes and very low seasonality as indicated by the Bolivina albatrossi/Uvigerina mediterranea Assemblage and lowest mean δ¹³C_H.elegans; (2) the Cape Ghir Upwelling Region with moderate to high paleoproductivity and paleo-C_org fluxes and low seasonality as indicated by the Bulimina mexicana/Gavelinopsis translucens Assemblage, and low mean δ¹³C_H.elegans; (3) the Cape Yubi Filament Region with moderate to high paleoproductivity, high paleo-C_org fluxes and high seasonality as indicated by the Cassidulina laevigata/Nonionella iridea Assemblage, and δ¹³C_H.elegans as low as those from the Cape Ghir Upwelling Region; (4) the Cape Ghir Filament Region with highest paleoproductivity, high paleo-C_org fluxes and seasonality as indicated by the Epistominella exigua Assemblage, and highest δ¹³C_H.elegans. Productivities during the LGM and today were compared based on faunal assemblages and Δδ¹³C values (Δδ¹³C = δ¹³C_LGM–δ¹³C_Present) of three infaunal species. Generally, during the LGM, the upwelling region was characterized by higher paleo-C_org fluxes, particularly in the area between the capes, similar seasonality along the coast, and higher seasonality further offshore than at present-day. For the reconstruction of LGM water mass stratification we used the δ¹³C of Cibicidoides wuellerstorfi and equilibrium adjusted δ¹⁸O of several species. Deep water mass stratification is characterized by glacial North Atlantic Central Water above 800 m, by glacial Mediterranean Outflow Water between 800 and 1900 m and glacial North Atlantic Deep Water below 1900 m and a southern source deep water mass. This means, considering the lowered glacial sea level, water mass stratification during the LGM was similar to present-day conditions.