A 1950-2100 Re-Evaluation of the Arctic Ocean Freshwater Budget’s Atmospheric Component

Freshwater in the Arctic region is in a delicate and complicated balance between the atmosphere, ocean, and terrestrial water cycles. One of the dominant sources of freshwater to the Arctic Ocean is net precipitation (precipitation minus evaporation), which accounts for more than a quarter of freshwater input into the Arctic Ocean. With the Arctic experiencing 2-3 times the global average climate warming, increased evaporation invariably results in a higher atmospheric water vapor content and can drastically alter or accelerate complex climate feedbacks in sea ice cover anomaly regions. Much of the previous work on atmospheric moisture variability in the Arctic has focused on quantifying the increasing precipitation trend, although differing time periods have led to discrepancies regarding the Arctic precipitation response. Combined with an increase in river runoff into the Arctic Ocean — which is the largest contributing freshwater source — the Arctic freshwater balance is in a state of flux and should be updated in the context of climate change and a warming Arctic.

We therefore re-evaluate the Arctic Ocean freshwater budget by quantifying how increasing precipitation advected into the Arctic region balances enhanced local recycling. Using ERA5, we quantify precipitation and evaporation rates from 1950 to 2019. We then utilize a bulk recycling formula for both monthly and annual regional recycling rates. Previously unreported for the Arctic Ocean as a whole, we determine Arctic precipitation recycling — the ratio of local to remote precipitation — to be approximately 25% in the 1950s and increasing 1% per decade. Additionally, we assess precipitation, evaporation, and recycled precipitation rates for seven individual regional Arctic seas, given the importance of declining sea ice areas in each of these areas. When scaled to a common area, the North Atlantic storm track unsurprisingly dominates Arctic recycling rates as a whole (greater than 40%), however, increasing and statistically significant precipitation, evaporation, and recycling rates are observed throughout the entire Arctic, with a strong Atlantic-versus-Pacific signal. By treating the sea ice area as a spatiotemporally variable surface cover, we also determine that declining sea ice cover in each specific Arctic subregion is a key factor in the strength of regional recycling rates with important implications for the Arctic freshwater budget and strong local climatic feedbacks near the sea ice margin.

In addition to the historical 1950–2019 period, we also calculate the precipitation recycling rates for the Arctic Ocean and associated subregions for 2015–2100 CMIP6 model output under shared socio-economic pathways 1-2.6, 2-4.5, and 5-8.5 emissions scenarios. With end-of-century projections for Arctic precipitation, evaporation, and the resulting precipitation recycling, we address the complex relationship between a declining sea ice cover and a moistening Arctic. By quantifying both the historical and projected future precipitation recycling for the Arctic, we provide an updated perspective of the atmospheric component of the Arctic Ocean freshwater budget under climate conditions, with local and remote implications.