Acceleration of the hydrological cycle with climate warming disrupts marine ecosystem function in the Arctic Ocean

One of the most robust changes in the hydrological cycle predicted by Earth System Models (ESMs) during the remainder of 21st century is an increase in the difference between precipitation and evapotranspiration (P-E) in arctic and boreal regions. Here we explore the long-term consequences of this change for marine ecosystems in the Arctic Ocean using the Community Earth System Model forced with a business as usual scenario of future greenhouse gas concentrations. We find that by the year 2300 increases in freshwater delivery considerably reduce Arctic Ocean surface salinity, creating a freshwater lens that has far-reaching impacts on marine biogeochemistry. The expanding freshwater lens limits vertical nutrient supply into the euphotic zone by enhancing vertical stratification and accelerating surface lateral mixing with surface waters in the North Atlantic, which become nutrient poor from weakening of the Atlantic meridional overturning circulation (AMOC). The resulting increase in nutrient stress reduces net export production in the Arctic Ocean by 53% in 2300 relative to the 1990s and triggers a shift in community composition with small phytoplankton replacing diatoms. Over the same period, the seasonal timing of marine productivity in the Arctic undergoes a 2 month forward shift, with the peak advancing from July to May. Our analysis suggests the threat to food webs and higher trophic levels may intensify after the year 2100 as gains in productivity from sea ice loss saturate and freshwater impacts on nutrient stress continue to strengthen. Our analysis highlights the critical importance of land-ocean hydrologic coupling as a driver of long-term biogeochemical change in the Arctic Ocean.