Evaluation and application of foraminiferal element/calcium ratios: Assessing riverine fluxes and environmental conditions during sapropel S1 in the Southeastern Mediterranean
- Research areas:
- Year:
- 2019
- Authors:
-
- Meryem Mojtahid
- R. Hennekam
- L. De Nooijer
- G. -J. Reichart
- Frans Jorissen
- W. Boer
- Sandrine Le Houedec
- G. J. De Lange
- Journal:
- Marine Micropaleontology
- Volume:
- 153
- Pages:
- 101783
- Month:
- December
- ISSN:
- 0377-8398
- 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 {\textless}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.
