A process study on the impact of the Arabian Sea oxygen minimum zone on organic matter degradation, nutrient regeneration, trace metal cycling and foraminiferal proxies
04 / 2008 - 03 / 2012
The Arabian Sea represents the iconic text book example of an open ocean oxygen minimum zone (OMZ). Low oxygen concentrations (down to less than 2 µM ) are found between 200 and 1000 meters water depth. This makes the northern Arabian a perfect natural laboratory to test the impact of oxygen depleted bottom waters on sediment organic matter processing, early diagenesis and the validity of proxies. Although the existence of the Arabian Sea OMZ is known for at least a century, the biological communities and the biogeochemical functioning of this system are still poorly understood. Low bottom-water oxygen concentrations have consequences for the organisms living at and within the sediments and consequently for the biogeochemical processes taking place. Here we propose to investigate the impact of oxygen depletion on organic matter processing and preservation and the recording of proxies by obtaining a set of multi cores along a transect through the OMZ on the slopes of a sub-marine mountain, the Murray Ridge and deploying sediment traps within and below the OMZ. Key objectives of the proposed research are: 1) to assess the impact of water column and bottom water oxygenation on organic matter degradation and transformation, in particular on specific biomarkers, 2) to identify the key organisms involved in organic matter processing under low-oxygen conditions and to link this to foraminiferal distribution patterns in order to evaluate and refine foraminiferal based proxies, 3) to investigate the impact of bottom water oxygenation on sedimentary nitrogen and phosphorus regeneration and trace metal cycling, 4) to assess the consistency and accuracy of diverse proxies (foraminifera, various organic biomarkers and trace metals) in recording bottom-water oxygen conditions.