| Summary: | The High Latitude North Atlantic is a globally significant region of deepwater formation home to intense primary productivity. Controls on phytoplankton growth in this region remain poorly constrained but are thought to seasonally be dominated by iron availability, with the potential to be influenced by predicted increases in sea surface temperatures. We conducted iron-temperature experiments in the Irminger Basin in late summer of 2021 to examine the impact of iron addition, with and without changes in temperature, on phytoplankton. We found clear evidence of iron limitation and that iron and temperature interactively impacted phytoplankton growth. Bacillariophyta responded to iron addition, and metaproteomic analyses revealed diverging strategies between Bacillariophyta and Prymnesiophyceae to iron-limiting conditions. Bacillariophyta deployed photosynthesis-related protein responses to manage iron stress regardless of changes in temperature. These interactive iron-temperature effects on phytoplankton growth have implications for the future of bloom progression and the biogeochemistry in this key marine region.
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