Figure 1. Idealized patterns of the dominant circulation regimes of the Arctic Ocean. Two simulated wind-driven circulation regimes of surface waters (anticyclonic—left; cyclonic—right) are shown in top panels. In the cyclonic regime (right panel) the clockwise circulation pattern (left panel) dominated during anticyclonic regime in the Beaufort Sea region (the Beaufort Gyre) weakens, and the flow across the basin, from the Siberian and Russian coasts to Fram Strait (the Transpolar Drift), shifts poleward. The cyclonic pattern dominated during 1989–1996; the anticyclonic pattern has prevailed since 1997. Isolines depict atmospheric sea level pressure distribution (hPa) typical for these climate regimes. Lower panel shows time series of the Arctic Ocean Oscillation (AOO) index and positive index values correspond to the year of anticyclonic circulation regime and negative – to the years of the cyclonic circulation regime. The Beaufort Gyre accumulates fresh water during anticyclonic circulation regime periods and releases it during cyclonic regimes.
	Figure 2. In 2007, the ocean surface circulation regime in the Beaufort Sea was strongly anticyclonic (clockwise) in winter (left) and summer (right) . Since the circulation of the sea ice cover and ocean surface layer are closely coupled and primarily wind-driven, this resulted in strong clockwise motion of sea ice in the Beaufort toward Fram Strait, where sea ice was flushed out of the Arctic Ocean at an unusually high rate. In winter the major flow stream removed sea ice from the Kara and Laptev Seas, while in the summer sea ice from the Canada Basin was transported out quickly by strong winds.
	Figure 3. In 2008, the ocean surface circulation regime in the central Arctic was anticyclonic (clockwise) in winter and summer (Figure 5c1). The intensity of motion was weaker than observed in 2007, consistent with changes in the observed sea level atmospheric pressure (SLP) patterns (see section 5b). In winter the major flow stream removed sea ice from the Kara and Laptev Seas, while in the summer sea ice from the Canada Basin was transported toward Fram Strait.
	Figure 4. Idealized patterns of the Arctic surface (blue arrows) and Atlantic water (red arrows) layers circulation. See discussion in Proshutinsky et al. (2005).

Results - Beaufort Gyre (BG) circulation

The Beaufort Gyre is an important circulation cell of the Arctic Ocean dynamics. Figure 1 illustrates idealized patterns of the two dominant wind-driven ocean circulation regimes: anticyclonic and cyclonic. Climatological studies (e.g., Proshutinsky and Johnson, 1997) provide a foundation for understanding the significance of these ocean surface conditions. These studies indicate that the Arctic Ocean surface layer currents are consistent with the Arctic atmosphere surface layer motion, alternating between cyclonic and anticyclonic circulation regimes. Each regime persists from 4 to 8 years, resulting in a period of 8-–16 years. The cyclonic pattern dominated during 1989-1996. Since 1997 the dominant regime has fluctuated, with an anticyclonic pattern being more prevalent (Fig. 1). Figures 1-9 show annual simulated wind-driven surface ice and ocean motion for 2000 through 2008. The Arctic Ocean Oscillation index (bottom panel in Figure 1) illustrates alternation of circulation regimes at a period of 8-16 years. During anticyclonic circulation regimes the BG region accumulates fresh water and during cyclonic regimes the BG region releases fresh water and this water could be available for transportation to the North Atlantic via Straits of Canadian Archipelago and Fram Strait.

The circulation of Pacific water (located at depths between 50 and 200 m) in the Arctic Ocean may be coherent with the surface currents, but its pathways are not known from direct observations.

The Atlantic water circulates in the Arctic Ocean at approximately 200–800m deep. This water penetrates to the Arctic via Fram Strait and St. Anna Trough (Barents Sea). Under extensive surface cooling, it sinks to intermediate depths and forms the warm Atlantic Layer, with water temperatures greater than 0°C. This layer is covered by low-density surface waters and is thus prevented from undergoing heat exchange with the atmosphere. The most widely accepted circulation scheme of Atlantic water (Rudels et al., 1994) postulates that it circulates counterclockwise, forming several loops in the Arctic basins (Fig. 4, red arrows). The variability of the Atlantic water circulation pattern is not known from observations, but model results show that its circulation has a pulsating character expressed in the propagation of warm and cold events, changing from seasonal to decadal time scales.

References

Proshutinsky, A. Yu., and M. Johnson, 1997. Two circulation regimes of the wind-driven Arctic Ocean. Journal of Geophysical Research, 102, 12,493–12,514.

Proshutinsky, A. et al., 2005. Arctic Ocean Study: Synthesis of model results and observations, Eos Transactions, American Geophysical Union, 86(40), 368, 370.

Rudels, B., Jones, E.P., Anderson, L.G. and Kattner, G., 1994. On the intermediate depth waters of the Arctic Ocean. In: O.M. Johannessen, R.D. Muench and J.E. Overland (Editors), The Polar Oceans and their role in shaping the global environment: the Nansen centennial volume. Geophysical Monograph 85. American Geophysical Union, Washington DC, USA, pp. 33-46.