Arctic Ocean freshwater: How robust are model simulations?

Abstract

[1] The Arctic freshwater (FW) has been the focus of many modeling studies, due to the potential impact of Arctic FW on the deep water formation in the North Atlantic. A comparison of the hindcasts from ten ocean-sea ice models shows that the simulation of the Arctic FW budget is quite different in the investigated models. While they agree on the general sink and source terms of the Arctic FW budget, the long-term means as well as the variability of the FW export vary among models. The best model-to-model agreement is found for the interannual and seasonal variability of the solid FW export and the solid FW storage, which also agree well with observations. For the interannual and seasonal variability of the liquid FW export, the agreement among models is better for the Canadian Arctic Archipelago (CAA) than for Fram Strait. The reason for this is that models are more consistent in simulating volume flux anomalies than salinity anomalies and volume-flux anomalies dominate the liquid FW export variability in the CAA but not in Fram Strait. The seasonal cycle of the liquid FW export generally shows a better agreement among models than the interannual variability, and compared to observations the models capture the seasonality of the liquid FW export rather well. In order to improve future simulations of the Arctic FW budget, the simulation of the salinity field needs to be improved, so that model results on the variability of the liquid FW export and storage become more robust.

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) …”

“…Several ice-ocean general circulation models show a decrease in net Arctic LFW exports since the 1990s, in particular through the Canadian Arctic Archipelago (Jahn et al, 2012). At the same time, the LFW storage in the upper Arctic Ocean basins increased between the 1990s and 2006-2008 (Rabe et al, 2011), further supported by several ice-ocean model simulations (Jahn et al, 2012) June and September, spanning more than a decade. The transports were derived using liquid freshwater component fractions from δ 18 O and nutrient observations (Dodd et al, 2012) together with velocities from an inverse model; the latter combines six hydrographic / velocity sections from observational campaigns between 1998 and 2011 as well as concurrent records from moored instruments.…”

“…Thompson and Wallace, 1998). Several ice-ocean general circulation models show a decrease in net Arctic LFW exports since the 1990s, in particular through the Canadian Arctic Archipelago (Jahn et al, 2012). At the same time, the LFW storage in the upper Arctic Ocean basins increased between the 1990s and 2006-2008 (Rabe et al, 2011), further supported by several ice-ocean model simulations (Jahn et al, 2012) June and September, spanning more than a decade.…”

“…3.2.4 indicate that the LFW component fractions strongly influence the LFW component transports in the Fram Strait. This is supported by the study of Arctic liquid freshwater storage and export in model simulations and moored observations, that partly focused on the Fram Strait (Jahn et al, 2012). Further studies of individual liquid freshwater components include the link of low FPW transports after 1998 and changes in the extent and the pathways of PW in the Arctic basins; in particular, a climate model simulation has shown that the pathways of PW exports from the Arctic are strongly related to the strength of the Beaufort Gyre (Jahn et al, 2010).…”

Sea ice assimilation into a coupled ocean–sea ice model using its adjoint

“…The representation of the Arctic Ocean circulation in existing ocean models considerably improved during the last 10 years, to the point that today many models reproduce the variability of SSH reasonably well (Koldunov et al, 2014), while for the components of the freshwater balance the picture is mixed (Jahn et al, 2012) and for circulation and water mass models show significant discrepancies .…”