Fate of ocean oxygenation in a warming world

点击翻译按钮获取中文摘要

Oxygen is critical to the health of all higher life. In the oceans dissolved oxygen concentrations have declined by 2% since 1960, and are expected to continue to decline into thefuture in relation to man-made climate change. Future deoxygenation, along with overfishing, threatens the sustainability of economically important fisheries and marineecosystems and will impact global biogeochemical cycles. It is therefore crucial that we obtain a well-informed view about what the future may hold.Current model simulations that predict the future carry considerable uncertainties; they do not all agree and grossly underestimate the documented decrease of the last 50 years. Thissuggests the models are missing key interactions, calling for urgent action and a dedicated and inclusive scientific approach.FARGO provides such an approach by addressing why, and to what extent, seawater dissolved oxygen concentrations may change in a warming world. FARGO is studyingdissolved oxygen concentrations in the Pacific Ocean, the largest low-oxic water body in the current ocean, through an innovative and dedicated research programmeincorporating a novel multi-proxy approach feeding IPCC-type climate model simulations across key warm time intervals:i- warmer climates across the closure of the American sea-way (4-15 million years);ii- warmer climates as future analogue (mid-Pliocene Warm Period; 3.3 to 3 million years ago, early Pliocene interglacials; 4.0-4.8 million years ago);iii- Pleistocene warm intervals (interglacials of the last ca. 800,000 years).During its first three years FARGO has made important advances to improve bottom water and subsurface water oxygen reconstructions using foraminifera (microorganisms). Some species float near the ocean surface, called planktonic foraminifera, we have made major advances in how trace elements of planktonic foraminifera may be used to understand changes in seawater oxygen levels. Species that live on or in sediments at the bottom of the ocean are termed benthic foraminifera and can be used to reconstruct bottom water oxygen concentrations and ventilation. Here we are also making major advancements, and are advancing various calibrations. FARGO's approach is however multidisciplinary, and we are applying a multiproxy approach to our reconstructions of seawater oxygen levels and also processes that drive this. We are using sediments from the International Ocean Discovery Program to determine if there have been changes in the natural extent and intensity of the shallow Pacific Ocean oxygen deficient zones (ODZ, e.g. areas where oxygen levels are too low to support aerobic life), during the key warm intervals. Furthermore FARGO is carrying out model simulations which help us understand how environmental changes (temperature, ocean circulation) impacted seawater oxygen not only for the Pacific, but also on a global scale. We are using two models to test the robustness of the model results and identification of model specific biases across each key time-period.The time-series generated by the proxy reconstructions will feed the IPCC-type climate model simulations and provide robust tests to investigate if the model simulations are realistic and correct for the specific time periods, and identify routes to improve the model simulations. Utilizing these improvements, FARGO will carry out simulations for future, including 1.5 and 2 degree warming scenarios.To raise awareness of ocean deoxygenation FARGO has several bespoke impact and engagement activities aimed at scientific peers, policy makers, and defined public audiences.