Quantitative reconstruction of past seawater oxygen concentrations

ongoing

Because of their sheer size and tight coupling to the atmosphere the oceans are a pivotal climate regulator. Their interaction with climate is associated with both physical processes such as ocean circulation, which redistribute heat, freshwater, and carbon around the globe, and biogeochemical processes, which ultimately control the strength of the biological carbon pump, and by inference the storage of remineralized carbon in the ocean interior. Seawater oxygen concentrations are intimately linked to both type of processes and are thus a crucial parameter for assessing the state of the oceans today but also in the past. Despite the crucial role these processes play on climate and climate variability, they remain surprisingly poorly understood. While paleoceanography offers a unique opportunity to observe the state and behaviour of the oceans under different boundary conditions, no reliable and widely applicable method for the quantitative reconstruction of past bottom water oxygen concentrations (BWO) has yet been established. Thus, the objective of OxyQuant is to develop and calibrate an innovative proxy toolkit to reliably reconstruct past BWO. To this end, three fundamentally independent approaches for which promising preliminary observations exist will be calibrated using a range of sediments retrieved from contrasted marine environments. While the first approach associated with the sedimentary concentrations of redox-sensitive trace metals, has already attracted much interest over the past decades, the other two methods, namely the organic matter – associated iodine and the stable isotope composition of authigenic cerium (δ142Ce) archived in fossilised fish debris, are novel and have yet to be comprehensively tested. Combined with their application in two case studies on glacial – interglacial time scales, OxyQuant will provide the paleoceanographic community with the means to finally fill the gap of quantitative reconstructions of past BWO.