A comparison of benthic foraminiferal Mn / Ca and sedimentary Mn / Al as proxies of relative bottom-water oxygenation in the low-latitude NE Atlantic upwelling system

[摘要] Trace element incorporation into foraminiferal shells (tests) is governed byphysical and chemical conditions of the surrounding marine environment, andtherefore foraminiferal geochemistry provides a means of palaeo-oceanographicreconstructions. With the availability of high-spatial-resolutioninstrumentation with high precision, foraminiferal geochemistry has become amajor research topic over recent years. However, reconstructions of pastbottom-water oxygenation using foraminiferal tests remain in their infancy.In this study we explore the potential of using Mn / Ca determined bysecondary ion mass spectrometry (SIMS) as well as by flow-through inductivelycoupled plasma optical emission spectroscopy (FT-ICP-OES) in the benthicforaminiferal species Eubuliminella exilis as a proxy for recordingchanges in bottom-water oxygen conditions in the low-latitude NE Atlanticupwelling system. Furthermore, we compare the SIMS and FT-ICP-OES resultswith published Mn sediment bulk measurements from the same sediment core.This is the first time that benthic foraminiferal Mn / Ca is directlycompared with Mn bulk measurements, which largely agree on the former oxygenconditions. Samples were selected to include different productivity regimesrelated to Marine Isotope Stage 3 (35–28 ka), the Last Glacial Maximum(28–19 ka), Heinrich Event 1 (18–15.5 ka), Bølling Allerød(15.5–13.5 ka) and the Younger Dryas (13.5–11.5 ka). ForaminiferalMn / Ca determined by SIMS and FT-ICP-OES is comparable. Mn / Ca washigher during periods with high primary productivity, such as during theYounger Dryas, which indicates low-oxygen conditions. This is furthersupported by the benthic foraminiferal faunal composition. Our resultshighlight the proxy potential of Mn / Ca in benthic foraminifera fromupwelling systems for reconstructing past variations in oxygen conditions ofthe sea floor environment as well as the need to use it in combination withother proxy records such as faunal assemblage data.

[学科分类] 地球化学与岩石