The large‐scale freshwater cycle of the Arctic

Abstract

This paper synthesizes our understanding of the Arctic's large‐scale freshwater cycle. It combines terrestrial and oceanic observations with insights gained from the ERA‐40 reanalysis and land surface and ice‐ocean models. Annual mean freshwater input to the Arctic Ocean is dominated by river discharge (38%), inflow through Bering Strait (30%), and net precipitation (24%). Total freshwater export from the Arctic Ocean to the North Atlantic is dominated by transports through the Canadian Arctic Archipelago (35%) and via Fram Strait as liquid (26%) and sea ice (25%). All terms are computed relative to a reference salinity of 34.8. Compared to earlier estimates, our budget features larger import of freshwater through Bering Strait and larger liquid phase export through Fram Strait. While there is no reason to expect a steady state, error analysis indicates that the difference between annual mean oceanic inflows and outflows (∼8% of the total inflow) is indistinguishable from zero. Freshwater in the Arctic Ocean has a mean residence time of about a decade. This is understood in that annual freshwater input, while large (∼8500 km3), is an order of magnitude smaller than oceanic freshwater storage of ∼84,000 km3. Freshwater in the atmosphere, as water vapor, has a residence time of about a week. Seasonality in Arctic Ocean freshwater storage is nevertheless highly uncertain, reflecting both sparse hydrographic data and insufficient information on sea ice volume. Uncertainties mask seasonal storage changes forced by freshwater fluxes. Of flux terms with sufficient data for analysis, Fram Strait ice outflow shows the largest interannual variability.

Liquid export of Arctic freshwater components through the Fram Strait 1998–2011

“…2.4). The average section LFW transport is at the higher end of published transport estimates from observations, which range from 28 to 95 mSv (Dickson et al, 2007;Serreze et al, 2006), and from high-resolution, coupled ice-ocean simulations (Jahn et al, 2012). In our surveys, mean MW section transports were about 130 % of LFW transports and FIFB about 60 % (FSIM about −60 %), whereas FPW (PW contribution to LFW) only contributed about 30 % (Table 4) …”

Arctic Ocean Circulation Patterns Revealed by GRACE

“…These values are further adjusted for underestimated freshwater fluxes by multiplying for a factor of 1.2 (Nguyen et al 2011). This adjustment helps the freshwater budget of the model to be closer to other estimates (e.g., Serreze et al 2006). Finally, neither PIOMAS nor ECCO2 includes the global-mean SLP, which is a term included in GRACE OBP.…”

Simulated Response of the Arctic Freshwater Budget to Extreme NAO Wind Forcing

“…We derive a freshwater budget for the model Arctic, based on the annual average of the 10-yr control integration, and compare its freshwater storage and release and exchanges with adjacent oceans to the observational Arctic freshwater budget of Serreze et al (2006). This observed freshwater budget offers an improvement over the original Arctic Ocean freshwater budget produced by Aagaard and Carmack (1989) by synthesizing large amounts of observational data gathered over the 1990s.…”

“…For historic reasons, the storage and fluxes of freshwater are calculated to a reference salinity of 34.8 psu-a value that approximates the average salinity of the Arctic Ocean (Aagaard and Carmack 1989). Serreze et al (2006) estimate the total liquid freshwater storage of the Arctic to be 74 000 km 3 (610%), with ;60% of this freshwater stored in the central Beaufort Sea, using the same PHC salinity dataset that we used to initialize our model. The large storage of freshwater in this region is visible by a ;20-m maximum thickness of freshwater when freshwater content is vertically integrated from the surface to the bottom (Fig.…”