Primary Versus Secondary Effects on the Chemical Composition of Planktonic Foraminifera: Insights from In-situ Analyses
Abstract
The chemical composition of planktonic foraminifera shells (tests) is widely used by paleoceanographers to infer past ocean environments. However, not all tests are equal with many species exhibiting thickened and non-thickened forms. This thickened layer, referred to as secondary calcite or a gametogenic crust, is thought to be added at a greater depth in the water column and is often chemically distinct from the primary calcite (e.g. Rosenthal et al., 2000). Furthermore, there is growing evidence that dissolution of test material can occur well above the lysocline because respiration of organic matter within marine sediments lowers the pH of their pore waters (e.g. deVilliers, 2005). Variations in the extent of both secondary calcification and post-depositional dissolution can therefore bias test chemistry-based records including even those from sediments thought to be free of diagenetic problems. We have examined the chemical composition of similar sized G. inflata, G. scitula and G. bulloides tests from ~48°N in the eastern north Atlantic using laser ablation ICP-MS and electron microprobe techniques. We compare the intratest variability of Mg/Ca and Sr/Ca between tests recovered from sediment traps located at ~3000m water depth (>1500m above the sea floor) and material recovered from Holocene sediments located at 2410m water depth. We discuss the implications of these observations for Mg/Ca-based temperature reconstructions and other trace element/Ca proxies. References: Y. Rosenthal et al. (2000) Paleocenography 15, No. 1, 135-145 S. deVilliers (2005) Deep-Sea Research I 52, 671-680
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFMPP11B1455H
- Keywords:
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- 4890 Zooplankton;
- 4924 Geochemical tracers;
- 4954 Sea surface temperature