SCANALOGUE_Geochemical scanning of climate change analogues to assess future hypoxia in restricted basins

Our aim is to deconvolve the effects of rapid changing sea level, sea surface temperatures, and evaporation/precipitation on the overturning circulations in restricted basins, which can potentially lead to low oxygen (hypoxic) conditions in these basins.

Temperature and the evaporation/precipitation balance determine surface-water buoyancy, thus water-column stratification, and thereby ventilation of deeper water. However, also sea-level changes are likely to impact water-column ventilation, particularly in restricted basins such as the Mediterranean and Red Seas. This potentially results in rapid drawdown of deep-water oxygen.

Reconstructing past water-column ventilation

We propose to reconstruct past water-column ventilation in the Mediterranean and Red Sea basins analyzing redox-sensitive trace elements in the sedimentary records. Short-term hypoxic events, in addition to the well-known sapropels, revealed in preliminary data are potentially linked to rapid climate and/or sea level changes. We will combine sediment geochemistry with trace metal analyses in benthic foraminiferal tests to identify precursor phases during which pore water oxygenation is reduced, but redox-sensitive elements have not yet accumulated in the sediment.

Calibrating the XRF core-scanner for sub-mm analyses of trace elements in wet sediments allows targeting high frequency variability (e.g. Dansgaard-Oeschger events). This is important as not only magnitude, but also rate of change is probably of major importance for water-column ventilation. State-of-the-art chronological control will be achieved through cross-calibration to the Soreq Cave speleothem records. Ultimately, we will combine our hypoxia reconstructions with O-GCM and conceptual box models to better define the thresholds where restricted seas shift into a basin-wide anoxic state, providing important constraints for future oceans.