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Zooplankton grazing of microplastic can accelerate global loss of ocean oxygen
Summary
Researchers modeled the effect of zooplankton microplastic ingestion on ocean oxygen levels, finding that reduced zooplankton grazing on phytoplankton due to plastic consumption could decrease export of organic carbon to depth, leading to lower oxygen consumption by deep-water bacteria and counterintuitively reducing oxygen loss in some scenarios.
Global warming has driven a loss of dissolved oxygen in the ocean in recent decades. We demonstrate the potential for an additional anthropogenic driver of deoxygenation, in which zooplankton consumption of microplastic reduces the grazing on primary producers. In regions where primary production is not limited by macronutrient availability, the reduction of grazing pressure on primary producers causes export production to increase. Consequently, organic particle remineralisation in these regions increases. Employing a comprehensive Earth system model of intermediate complexity, we estimate this additional remineralisation could decrease water column oxygen inventory by as much as 10% in the North Pacific and accelerate global oxygen inventory loss by an extra 0.2-0.5% relative to 1960 values by the year 2020. Although significant uncertainty accompanies these estimates, the potential for physical pollution to have a globally significant biogeochemical signal that exacerbates the consequences of climate warming is a novel feedback not yet considered in climate research.
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