By 2300, climate change may cause fishery yields to decline by as much as 20% around the globe, and by as much as 60% in the North Atlantic, a new modeling study suggests. The study primarily attributes this decline to a lack of ocean mixing, such that nutrients sink into the deep ocean instead of staying at the ocean surface; such alterations to ocean mixing would ultimately drive a decline in fish populations near the surface, the authors say. Climate change models consistently estimate that fisheries will decline by the end of this century, yet there have been few efforts to explore what changes might occur beyond 2100. Here, J. Keith Moore and colleagues used modeling to explore the effects of climate change on fisheries under a "business-as-usual" scenario whereby carbon emissions continue apace, at the same level as they are now. The Southern Ocean currently experiences mixing between the bottom and top oceanic layers, delivering such a substantial amount of nutrients to the surface that an abundance flows into other oceans. However, simulations by Moore et al. suggest that a combination of changing winds and warmer upper oceanic layers, plus a poleward shift of nutrient upwelling in the Antarctic, will cause an increased portion of nutrients to sink into the deeper layer of the ocean and become trapped there (for example, the amount of phosphate being upwelled will be reduced by 41%, the model estimates). This will reduce the delivery of nutrients to other oceanic areas, they note. While ocean warming and stratification will increase globally, deep mixing in the North Atlantic will be particularly reduced, the authors find. They note that the long-term effects of these changes mean that fisheries will be reduced for a thousand years or more. Charlotte Laufkötter and Nicolas Gruber discuss this study in a related Perspective.
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