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
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AuthorMcKay, C. L.; Groeneveld, J.; Filipsson, H. L.; Gallego-Torres, Daniel; Whitehouse, M. J.; Toyofuku, T.; Romero, O. E.
Copernicus Publications; European Geosciences Union (EGU)
Northern Arabian seaPaleothermometryMediterranean sapropelManganese carbonateTemperature
McKay, C.L.; et al. 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. Biogeosciences, 12(18): 5415-5428 (2015). [http://hdl.handle.net/10481/38573]
SponsorshipWe would like to thank the NORDSIM laboratory (a joint Nordic infrastructure operated under an agreement regulated by NOS-N) for granting analytical time and to Lev Ilyinsky and Kerstin Lindén for their support. This work is NordSIM contribution no. 411.We also thank Mike Hall for foraminiferal test cross-sectioning and also Ed Hathorne and Dave Heslop for flowthrough assistance. This research was funded by the Crafoord Foundation (20100547), the Lund University Centre for Studies of Carbon Cycle and Climate Interactions (LUCCI) and Kungl. Fysiografiska Sällskapet i Lund. H. L. Filipsson and J. Groeneveld acknowledge support from the Swedish Research Council VR (621-2011-5090) as well as funding from the Strategic Research Area Biodiversity and Ecosystem Services in a Changing Climate (BECC). D. Gallego-Torres acknowledges the JAE programme from the CSIC and programme FEDER R5/10FOR/2014 (Junta de Andalucía).
Trace element incorporation into foraminiferal shells (tests) is governed by physical and chemical conditions of the surrounding marine environment, and therefore foraminiferal geochemistry provides a means of palaeo-oceanographic reconstructions. With the availability of high-spatial-resolution instrumentation with high precision, foraminiferal geochemistry has become a major research topic over recent years. However, reconstructions of past bottom-water oxygenation using foraminiferal tests remain in their infancy. In this study we explore the potential of using Mn / Ca determined by secondary ion mass spectrometry (SIMS) as well as by flow-through inductively coupled plasma optical emission spectroscopy (FT-ICP-OES) in the benthic foraminiferal species Eubuliminella exilis as a proxy for recording changes in bottom-water oxygen conditions in the low-latitude NE Atlantic upwelling system. Furthermore, we compare the SIMS and FT-ICP-OES results with published Mn sediment bulk measurements from the same sediment core. This is the first time that benthic foraminiferal Mn / Ca is directly compared with Mn bulk measurements, which largely agree on the former oxygen conditions. Samples were selected to include different productivity regimes related 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). Foraminiferal Mn / Ca determined by SIMS and FT-ICP-OES is comparable. Mn / Ca was higher during periods with high primary productivity, such as during the Younger Dryas, which indicates low-oxygen conditions. This is further supported by the benthic foraminiferal faunal composition. Our results highlight the proxy potential of Mn / Ca in benthic foraminifera from upwelling systems for reconstructing past variations in oxygen conditions of the sea floor environment as well as the need to use it in combination with other proxy records such as faunal assemblage data.