A. Proshutinsky1, M.-L. Timmermans2, I. Ashik3, A. Beszczynska-Moeller4, E. Carmack5, I. Frolov3, R. Krishfield1, F. McLaughlin5, J. Morison6, I. Polyakov7, K. Shimada8, V. Sokolov3, M. Steele6, J. Toole1, and R. Woodgate6
1Woods Hole Oceanographic Institute, Woods Hole, MA
In 2009 the annual wind-driven Arctic Ocean circulation regime was cyclonic for the first time since 1997. This regime significantly influenced the characteristics of the sea ice cover and ocean: maximum upper ocean temperatures in summer 2009 continued to decline relative to the historical extreme warm conditions observed in summer 2007; surface-layer waters in the Arctic Ocean in 2009 remained much fresher than in the 1970s and were comparable to 2008 conditions; and the sea level along the Siberian coastline significantly decreased relative to 2008. An interesting change in ocean geochemistry was observed in the Canada Basin. The combination of an increase in the amount of melt water from the sea ice cover and CO2 uptake (acidification) in the ocean caused the surface waters of the Canada Basin to become corrosive to calcifying organisms.
In 2009, the annual wind-driven ocean circulation regime can be characterized as cyclonic (counterclockwise), with a Beaufort Gyre that is significantly reduced in strength and a Transpolar drift that is effectively nonexistent (Fig. O.1). This is the first time that an annual cyclonic circulation regime has been observed in the Arctic since 1997. The anticyclonic circulation regime that persisted through 2008 lasted at least 12 years instead of the typical 5–8 year pattern [as reported in Proshutinsky and Johnson (1997), who analyzed statistics of Arctic circulation regimes between 1948 and 1989]. The climatological seasonal cycle of the Arctic has anticyclonic ice and ocean circulation prevailing in winter and cyclonic circulation in summer. Since 2007, this seasonality has changed dramatically. In 2007, both summer and winter circulations were very strongly anticyclonic (Fig. O.1, top panels) and resulted in the unprecedented reduction of the Arctic Ocean summer sea ice cover. In 2008, the winter circulation was anticyclonic but the summer circulation was unusual with a well-pronounced Beaufort Gyre and a cyclonic circulation cell north of the Laptev Sea (Fig. O.1, middle panels). In 2009 (Fig. O.1, bottom panels), the circulation reversed relative to climatology in both winter and summer: it was anticyclonic in summer (instead of cyclonic) and cyclonic in winter (instead of anticyclonic). These wind-driven conditions significantly influenced the characteristics of the sea ice cover, oceanic currents, ocean freshwater and heat content observed during 2007–09.
Water temperature and salinity
Maximum upper ocean temperatures in summer 2009 continued to decline since the historical extreme in summer 2007 (Fig. O.2). This tendency is strongly linked to changes in the characteristics (e.g., pace and location) of the summer sea ice retreat and their effect on local atmospheric warming (Steele et al. 2010, manuscript submitted to J. Geophys. Res.). Surface warming and sea ice reduction in the Canada Basin has also been accompanied by the widespread appearance of a near-surface temperature maximum at 25–35 m depth due to penetrating solar radiation (Jackson et al. 2010). As described in the Arctic atmosphere section, the heat accumulated in the surface and near-surface layers of the ocean can be released back into the atmosphere in the fall—a cycle that is likely to influence sea ice conditions in the future.
Surface-layer waters in the Arctic Ocean in 2009 remained much fresher than in the 1970s (Timokhov and Tanis 1997, 1998). In the Beaufort Gyre, freshwater content in 2009 (Fig. O.3) was comparable to the 2008 freshwater conditions, with the exception of the southwest corner of the Canada Basin. In this region, the freshwater accumulation was increased relative to 2008 by approximately 0.4 km3 under enhanced Ekman pumping and sea ice melt in this region. In total, during 2003–09 the Beaufort Gyre (Proshutinsky et al. 2009) has accumulated approximately 5000 km3 of freshwater (from 17 300 km3 in 2003 to 22 300 km3 in 2009), which is 5800 km3 larger than climatology of the 1970s (Timokhov and Tanis 1997, 1998).
Hydrographic surveys conducted in 2007–09 summer (Fig. O.3) in the Canada Basin indicate that in 2007 and 2008 there were two shallow temperature maximums in the upper Pacific water layer. However, in 2009, the heat content in this layer was reduced.
Atlantic Water layer maximum temperature anomalies for 2007–09 (Fig. O.4) were calculated relative to the 1970s (Timokhov and Tanis 1997, 1998; Polyakov and Timokhov 1994). The 2007–09 Atlantic Water layer data were derived from ship-based and Ice-Tethered Profiler (ITP) instruments. In 2007–09, the temperature anomalies were generally higher on the Eurasian side of the Lomonosov Ridge, reaching a maximum of up to 1.5°C along the Eurasian Basin boundaries. Warming was less pronounced in the Canada Basin. There was little to no temperature anomaly (<0.1°C) at the southeast boundary of the Canada Basin or in the basin boundary regions adjacent to Greenland and the Canadian Archipelago. Negative (cooling) temperature anomalies were detected in the vicinity of Nares Strait. Considering 2009 data alone, the warming pattern remained similar with the major difference being that maximum temperature anomalies along the Eurasian Basin boundaries were lower (<1.0°C).
The characteristics of the Atlantic Water layer discussed above are regulated by the Atlantic water parameters in the Fram Strait (Fig. O.5), where the Atlantic water inflows to the Arctic Ocean. After reaching a maximum in 2006, the temperature of Atlantic water in Fram Strait decreased until 2008. In 2009, Atlantic water temperature and salinity in the northern Fram Strait started to rise again, returning to their long-term means. The late winter of 2008 and early spring of 2009 were also characterized by a higher Atlantic water volume inflow with the West Spitsbergen Current as compared to 2005–07 (Fig. O.5).
The Bering Strait is another important gateway to the Arctic Ocean. Preliminary analysis of mooring data from the Bering Strait does not suggest a repeat of the very high heat fluxes from 2007 (Woodgate et al. 2010). Temperatures in 2008 were generally cooler than in 2007, reaching only 2°C–3°C in near-bottom temperature, compared to 4°C–5°C in 2007. Similarly, by the time of mooring turn-around in 2009, water temperatures were about a degree colder than the same month (August) in 2007. These cooler temperatures are more in agreement with temperatures of 2000–06 in the strait.
An interesting change in ocean geochemistry was observed in the Canada Basin in 2008 and 2009. The input of sea ice meltwater, in combination with CO2 uptake and global ocean acidification, caused the surface waters of the Canada Basin to become corrosive to calcifying organisms in the upper layer in 2008 (Yamamoto-Kawai et al. 2009). This is the first deep basin observation of aragonite undersaturation in surface waters. In 2009 the areal extent of surface waters unsaturated in aragonite, a form of calcium carbonate produced by marine organisms, increased. The increased stratification and decrease in upper-layer nutrient concentrations has also resulted in an increase in the number of picoplankton and a decrease in nanoplankton. Shifts such as these may alter the food web in the future (Li et al. 2009).
Figure O.6 shows sea level (SL) time series from nine coastal stations in the Siberian Seas, having representative records for the period of 1954–2009 (Arctic and Antarctic Research Institute data archives). In 2009, the SL along the Siberian coastline has significantly decreased relative to 2008. This caused a slight reduction in the estimated rate of SL rise for the nine stations over the period, to 2.57 ± 0.45 mm yr−1 (after correction for glacial isostatic adjustment, GIA). The changing SL rise tendency may be due to the substantial change in the wind-driven ocean circulation regime (less anticyclonic, as described in section 5c1) and/or due to steric effects associated with the reduction of surface ocean warming and freshening rates (section on Water temperature and salinity, above). Ocean cooling and salinification both result in sea level decrease.
Jackson, J. M., E. C. Carmack, F. A. McLaughlin, S. E. Allen, and R. G. Ingram, 2010: Identification, characterization, and change of the nearsurface temperature maximum in the Canada Basin, 1993-2008. J. Geophys. Res., 115, C05021, doi:10.1029/2009JC005265.
Li, W. K., F. A. McLaughlin, C. Lovejoy, and E. C. Carmack, 2009: Smallest algae thrive as the Arctic Ocean freshens. Science, 326, 539.
Polyakov, I. V., and L. A. Timokhov, 1994: Mean fields of temperature and salinity of the Arctic Ocean. Russian Meteor. Hydrol., 7, 33–38.
Proshutinsky, A. Y., and M. A. Johnson, 1997: Two circulation regimes of the wind-driven Arctic Ocean. J. Geophys. Res., 102 (C6), 12 493–12 514.
——, and Coauthors, 2009: Beaufort Gyre freshwater reservoir: State and variability from observations J. Geophys. Res., 114, C00A10, doi:10.1029/2008JC005104.
Timokhov, L., and F. Tanis, Eds., 1997: Environmental Working Group Joint U.S.-Russian Atlas of the Arctic Ocean-Winter Period. Environmental Research Institute of Michigan in association with the National Snow and Ice Data Center, CD-ROM.
——, and ——, Eds., 1998: Environmental Working Group Joint U.S.-Russian Atlas of the Arctic Ocean-Summer Period. Environmental Research Institute of Michigan in association with the National Snow and Ice Data Center, CD-ROM.
Yamamoto-Kawai, M., F. McLaughlin, E. Carmark, S. Nishino, and K. Shimada, 2009: Aragonite undersaturation in the Arctic Ocean: Effects of ocean acidification and sea ice melt. Science, 326, 1098–1100.