Evaluation and application of foraminiferal element/calcium ratios: Assessing riverine fluxes and environmental conditions during sapropel S1 in the Southeastern Mediterranean
Mojtahid, M.; Hennekam, R.; de Nooijer, L.J.; Reichart, G.-J.; Jorissen, F.; Boer, W.; Le Houedec, S.; de Lange, G.J. (2019). Evaluation and application of foraminiferal element/calcium ratios: Assessing riverine fluxes and environmental conditions during sapropel S1 in the Southeastern Mediterranean. Mar. Micropaleontol. 153: 101783. https://dx.doi.org/10.1016/j.marmicro.2019.101783 In: Marine Micropaleontology. Elsevier: Amsterdam; New York; Oxford; Tokyo. ISSN 0377-8398; e-ISSN 1872-6186, more |  |
| Author keywords | Sapropel S1; Levantine basin; Productivity; Oxygenation; Salinity; Stable isotopes; Mg/Ca; Ba/Ca; Mn/Ca; Na/Ca |
| Authors | | Top | - Mojtahid, M.
- Hennekam, R., more
- de Nooijer, L.J., more
- Reichart, G.-J., more
| - Jorissen, F.
- Boer, W., more
- Le Houedec, S.
- de Lange, G.J.
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| Abstract | Paleostudies often rely on foraminiferal calcite chemistry, which reflect past sea water condition through so-called proxy relationships. One way to evaluate robustness of these proxy relationships is to test them in well-studied and during well-constrained climate transitions. The southeastern (SE) Mediterranean is a perfect natural laboratory with a large range of past environmental conditions. These range from low productivity well-ventilated waters like they are at present, to poorly ventilated, high productivity conditions during sapropels. We here explore the reliability of recently developed foraminiferal-based proxies (Ba/Ca, Mn/Ca, Na/Ca) as tracers for changes in productivity, oxygenation and salinity during the most recent sapropel S1. We use laser ablation ICP-MS analyses of the planktonic G. ruber and six benthic species (B. alata, G. affinis, G. altiformis, G. orbicularis, H. boueana, U. peregrina). Our results show that planktonic Ba/Ca is a reliable tracer for Ba2+-enriched Nile outflow, where benthic Ba/Ca traces enhanced paleo(export) productivity relatively well. The interpretation of Mn/Ca data is less straightforward, and the low values may suggest a lower precipitation of Mn-oxides under prevailing hypoxia. The decrease in planktonic and benthic Na/Ca is coherent with excess Nile runoff lowering salinities in the <500m water column. However, when applying the existing calibrations, unrealistic salinity values are found, highlighting potential secondary controls on Na-incorporation. Benthic Ba/Ca time series analyses highlight a multicentennial variability in paleo(export) productivity, consistently with redox proxies. We conclude that benthic Ba/Ca records the close coupling between Ba cycling, export productivity, and redox conditions during S1 in the SE Mediterranean. |
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