For the last decade, increases in the Arctic Ocean's primary production have been driven by an increased abundance of phytoplankton rather than sea ice loss, indicating an influx of new nutrients into the region's relatively nutrient-deprived waters, researchers report. The results suggest that the Arctic Ocean (AO) could become more productive and efficient at exporting inorganic carbon to the deep ocean in the future. Due to the drastic loss of sea ice and warming sea temperatures in the Arctic for the last several decades, phytoplankton abundance in the AO has risen significantly, leading to the observed increases in primary production (PP) across the region. However, it's debated how climate change will continue to impact Arctic PP. Some argue that the increased freshwater inputs that accompany Arctic warming could intensify AO stratification, preventing the mixing of critical deepwater nutrients phytoplankton biomass requires, thus constraining PP potential. Others, however, suggest that greater expanses of open water and more frequent storms may instead enhance PP, by driving increased vertical mixing and the transport of new nutrients from other ocean regions into Arctic waters. The color of ocean water, which can be observed from space, can be used to estimate plankton biomass; here, Kate Lewis and colleagues used an ocean color algorithm to analyze satellite images of the AO to evaluate the effects of climate change on Arctic PP over the last 20 years. Lewis et al. show that the region's PP increased by 57% between 1998 and 2018 - a finding that far exceeds previous estimates. Over the first decade of the time series, the authors confirm that increased PP was largely due to sea ice loss. Surprisingly, however, increases observed during the following decade were instead driven by increases in plankton biomass, suggesting an influx of new nutrients into some - but not all - regions of the AO. In a related Perspective, Marcel Babin discusses the study's findings and the further questions they raise. "The rest of this story will stem from longer time series and a better grasp of the physical phenomena that control nutrient concentrations," Babin writes.
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Journal
Science