Paper No. 41-8
Presentation Time: 9:00 AM-5:30 PM
RECONSTRUCTING SOUTHEASTERN MEDITERRANEAN BOTTOM AND SURFACE WATER ENVIRONMENTS DURING SAPROPEL S1 USING LASER-ICPMS ELEMENTAL RATIOS ON FORAMINIFERAL SHELLS
To improve climate projections in the current context of climate change, our understanding of processes controlling the physics of ocean-atmosphere exchange needs to advance. Studying past environmental changes is the key to understand ocean circulation patterns. Proxies for reconstructing seawater temperatures are relatively well-developed, whereas those for past salinity, productivity, and bottom-water oxygen levels do not yet allow sufficiently detailed reconstructions. In this study, we explore the potential of using Mg/Ca, Na/Ca, Ba/Ca, and Mn/Ca measured by Laser Ablation (LA) ICP-MS on foraminiferal shells as proxies for reconstructing past changes in temperature, salinity, productivity and deep-water oxygenation. The eastern Mediterranean provides an ideal natural laboratory to perform such a study as it is characterized by extreme shifts in overturning circulation and periodical anoxia, leading to the formation of organic-rich sediment layers, i.e. sapropels. Deposition of sapropels probably requires both (1) freshwater flooding leading to stagnant bottom waters with reducing conditions, and (2) high primary production. The present study focuses on the most recent sapropel (S1) from a marine core located in the southeastern Levantine Basin. This core was earlier studied for its bulk sedimentary geochemistry, and planktonic foraminiferal assemblages and stable isotopes. Our study presents a unique dataset of LA-ICP-MS elemental ratios performed on six benthic and one planktonic foraminiferal species, which are compared with the relatively well-known water-column characteristics during S1 deposition. For instance, the simultaneous increase in sedimentary Ba and incorporated Ba in benthic foraminiferal tests points to a close coupling between Ba cycling and export productivity. The synchronized decrease in surface water salinities and incorporated Na in planktonic tests reveals the high potential of this innovative method to reconstruct paleo-salinities.