Circulation Pathways and Exports of Arctic River Runoff Influenced by Atmospheric Circulation Regimes

Abstract

River runoff supplies the Arctic Ocean with a large amount of freshwater and land-derived material, so it is important for both the physical and biogeochemical marine environment. In this study, we used wind perturbation simulations to elucidate the response of the circulation pathways and exports of Arctic river runoff to different atmospheric circulation regimes. Specifically, wind perturbations representing the negative and positive phases of the Arctic Oscillation and Beaufort High modes were imposed over the Arctic Ocean separately in different sensitivity experiments. In addition, some combinations of the two modes were also considered in sensitivity experiments. By comparing these experiments with a control simulation, we revealed the impact of different wind perturbations. The atmospheric circulation regimes influence the Arctic surface geostrophic currents through changing the halosteric height, which is associated with the changes in spatial distribution of surface freshwater. The circulation pathways of river runoff, and Pacific and Atlantic derived surface waters are mainly determined by the surface geostrophic currents. The positive (negative) Arctic Oscillation reduces (increases) freshwater storage and sea surface height in the Makarov and Eurasian basins, thus strengthening (weakening) the cyclonic circulation and weakening (strengthening) the anticyclonic circulation; Accordingly, the Eurasian runoff leaves the Siberian shelf at more eastern (western) locations, and has an enhanced export through the Fram Strait (Canadian Arctic Archipelago). The positive (negative) Beaufort High increases (reduces) freshwater storage and sea surface height in the Amerasian Basin, thus strengthening (weakening) the anticyclonic circulation; Accordingly, the Eurasian runoff export through the Fram Strait and the Mackenzie River runoff export through the Canadian Arctic Archipelago are reduced (increased). The positive Arctic Oscillation increases freshwater available to the Beaufort Gyre, which can be efficiently accumulated there in the presence of a positive Beaufort High forcing. The impact of the Beaufort High mode on the location of the Transpolar Drift Stream and runoff circulation pathways is stronger with a positive Arctic Oscillation than with a neutral Arctic Oscillation state. Our results also showed that Eurasian runoff can only have a relatively small contribution to freshwater accumulation in the Beaufort Gyre region.

A Synthesis of the Upper Arctic Ocean Circulation During 2000–2019: Understanding the Roles of Wind Forcing and Sea Ice Decline

“…This can be explained by the weak but positive sea level pressure anomaly in the central Arctic basin averaged over the past 20 years (Figure S9). The sea level pressure anomaly roughly resembles a negative Arctic Oscillation pattern, which tends to shift the surface freshwater circulation pathway from the Amerasian Basin towards the Eurasian Basin (Wang et al, 2021b). The sea ice decline completely changes this tendency.…”

“…Changes in ocean inflow from the North Pacific and North Atlantic could also influence the upper ocean circulation in the Arctic Ocean (Spall, 2020;Karami et al, 2021;Wang et al, 2021b). For example, stronger Pacific Water inflow through the Bering Strait can increase the sea surface height along the continental slope of the Canada Basin so that the ocean circulation towards the Canadian Arctic Archipelago and Fram Strait is strengthened (Spall, 2020;Wang et al, 2021b).…”

“…Model studies also demonstrate that the Arctic Oscillation can influence the strength and spatial extent of the cyclonic ocean circulation, which further impacts the location of the Transpolar Drift Stream and the spatial extent of the anticyclonic circulation (Wang et al, 2021b). The strength of the Beaufort High mainly influences the anticyclonic circulation, and it can influence the location of the Transpolar Drift Stream only when the Arctic Oscillation has been strongly positive for a long time so that the Transpolar Drift Stream has been shifted close to the Alpha-Mendeleev Ridge (Wang et al, 2021b). The cyclonic and anticyclonic ocean circulations are not isolated from each other by the Transpolar Drift Stream, but possibly interconnected through mesoscale eddies as suggested by both observations and idealized model simulations (Timmermans et al, 2008;Spall, 2020).…”

“…This situation happened in the 1990s as revealed by hydrography observations (Carmack et al, 1995;Morison et al, 1998;Steele and Boyd, 1998;Ekwurzel et al, 2001;McLaughlin et al, 2002) and model simulations (Maslowski et al, 2000), which can be explained by the highest Arctic Oscillation of the longest duration (from 1989 to the mid 1990s) at least for the past six decades (Figure 3A). Dynamically, an eastward shift of the Transpolar Drift Stream is a result of the reduction in the halosteric height (that is, reduction in the liquid FWC) in the Makarov Basin induced by strongly positive Arctic Oscillation (Wang et al, 2021b). Following the weakening of the Arctic Oscillation in the second half of the 1990s, the ocean condition became similar to the pre-1990s climatology after 2000, with the Transpolar Drift Stream moving back to the Lomonosov Ridge as revealed by hydrography and chemical tracer observations (Steele et al, 2004;Morison et al, 2006;Alkire et al, 2007).…”

On the Interplay between Freshwater Content and Hydrographic Conditions in the Arctic Ocean in the 1990s–2010s

“…According to the authors, the mean FWC trend calculated using S ref = 35.0 based on monthly gridded fields between 1992 and 2012 was about 600 ± 300 km 3 yr −1 , which is equivalent to the 16,800 ± 8400 km 3 increase in FWC estimated for the period covered by our observations. We speculate that the freshening in the Arctic Ocean will continue since several observation-and model-based studies have suggested an increasing trend in the freshwater supply to the Arctic under warming climate due to increasing atmospheric moisture transport from lower latitudes and increased river runoff [50][51][52][53][54].…”