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  1. Historically, sea ice loss in the Arctic Ocean has promoted increased phytoplankton primary production because of the greater open water area and a longer growing season. However, debate remains about whether primary production will continue to rise should sea ice decline further. Using an ocean color algorithm parameterized for the Arctic Ocean, we show that primary production increased by 57% between 1998 and 2018. Surprisingly, whereas increases were due to widespread sea ice loss during the first decade, the subsequent rise in primary production was driven primarily by increased phytoplankton biomass, which was likely sustained by an influx of new nutrients. This suggests a future Arctic Ocean that can support higher trophic-level production and additional carbon export.

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  2. Abstract

    As the physical environment of the Arctic Ocean shifts seasonally from ice‐covered to open water, the limiting resource for phytoplankton growth shifts from light to nutrients. To understand the phytoplankton photophysiological responses to these environmental changes, we evaluated photoacclimation strategies of phytoplankton during the low‐light, high‐nutrient, ice‐covered spring and the high‐light, low‐nutrient, ice‐free summer. Field results show that phytoplankton effectively acclimated to reduced irradiance beneath the sea ice by maximizing light absorption and photosynthetic capacity. In fact, exceptionally high maximum photosynthetic rates and efficiency observed during the spring demonstrate that abundant nutrients enable prebloom phytoplankton to become “primed” for increases in irradiance. This ability to quickly exploit increasing irradiance can help explain the ability of phytoplankton to generate massive blooms beneath sea ice. In comparison, phytoplankton growth and photosynthetic rates are reduced postbloom due to severe nutrient limitation. These results advance our knowledge of photoacclimation by polar phytoplankton in extreme environmental conditions and indicate how phytoplankton may acclimate to future changes in light and nutrient resources under continued climate change.

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