At a Glance
The Resplandy group studies global change in the biogeochemistry of the oceans and how this will affect other parts of the Earth system, with emphasis on the cause, magnitude, stability and longevity of the ocean carbon sink. In the last year, the Resplandy group’s research focused on the ocean’s response to climate change, in particular the ocean’s loss of oxygen associated with warming. They studied how this warming trend influences ecosystems, ecosystem services (e.g., fisheries) and the climate itself via the production of nitrous oxide, which occurs in low oxygen ocean waters. This work led to three publications in 2022, including one highlighted by the American Geophysical Union Newsroom that focuses on the fate of oxygen minimum zones and coastal “dead zones,” which are open ocean and coastal ocean areas with very low oxygen levels unsuitable for most organisms. It is important for companies and policymakers to learn how oxygen minimum zones may behave in a warming world and how plans for the energy transition may impact these zones.
The ocean has lost dissolved oxygen as a result of global warming in the past 50 years. A serious threat of this systematic ocean deoxygenation is the expansion of tropical oxygen minimum zones (OMZs) located in the subsurface ocean (Figure 6.1). An equally serious and more frequent threat is the occurrence of coastal dead zones, places where pollution originating from land, such as fertilizers, urbanization and wastewater, reinforces the depletion of oxygen. Uncertainties in the spatial and temporal evolution of OMZs and coastal dead zones severely restrict the ability to anticipate their ecological, climatic and societal impacts (Resplandy, 2018).
In this project, the Resplandy group leveraged state-of-the-art observations, the latest generation of Earth System Models (CMIP6 ESMs) and newly developed ocean model simulations to examine the evolution of the tropical OMZs in the global ocean and coastal dead zones in the densely populated and understudied Indian Ocean. A major outcome of this work is the first robust projections of tropical OMZs. This was achieved using a more holistic approach than the one used in prior work and that considers the different layers of the OMZs.
Another major finding is the crucial role of natural climate variability and ocean physical and biological complexity, such as ocean turbulence and ecosystem structure. These factors can reinforce and/or offset the effect of climate change on oxygen minimum zones and coastal dead zones, and ultimately influence the risk for ecosystems.
Busecke, J.J.M., J. Resplandy, S.L. Ditkovsky, and J.G. John, 2022. Diverging fates of the Pacific Ocean oxygen minimum zone and its core in a warming world. AGU Advances 3:e2021AV000470. (https://doi.org/10.1029/2021AV000470).
Lévy, M., L. Resplandy, J.B. Palter, D. Couespel, and Z. Lachkar, 2022. Chapter 13: The crucial contribution of mixing to present and future ocean oxygen distribution. Ocean Mixing (329–344). Elsevier. (https://doi.org/10.1016/B978-0-12-821512-8.00020-7).
Pearson, J., L. Resplandy, and M. Poupon, 2022. Coastlines at risk of hypoxia from natural variability in the Northern Indian Ocean. Global Biogeochemical Cycles 36(6):e2021GB007192. (https://doi.org/10.1029/2021GB007192).
Resplandy, L., 2018. Will ocean zones with low oxygen levels expand or shrink? Nature 557:314–315. (https://doi.org/10.1038/ d41586-018-05034-y).
Climate change will cause Pacific’s low-oxygen zone to expand even more by 2100, 2022. AGU Newsroom website (accessed Jan. 5, 2023).