Technical Notes 1–7 > Figure TN1

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Supporting Online Materials for Oceanography Volume 25, Issue 3, September 2012

Recent Arctic Climate Change and Its Remote Forcing of Northwest Atlantic Shelf Ecosystems

By the Marine Ecosystem Responses to Climate In the North Atlantic (MERCINA) Working Group | Charles H. Greene, Bruce C. Monger, Louise P. McGarry, Matthew D. Connelly, Neesha R. Schnepf, Andrew J. Pershing, Igor M. Belkin, Paula S. Fratantoni, David G. Mountain, Robert S. Pickart, Rubao Ji, James J. Bisagni, Changsheng Chen, Sirpa M.A. Hakkinen, Dale B. Haidvogel, Jia Wang, Erica Head, Peter Smith, and Alessandra Conversi

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TECHNICAL NOTES

1. The Arctic Oscillation (AO) is the coupling between atmospheric and oce- 4. The distance from the Canadian most important mode of interannual to anic circulation with the rapid decline in Arctic Archipelago to Georges Bank interdecadal climate variability above the sea ice thickness and extent since 1980 is ~ 5,000 km. Estimated propaga- Arctic Circle and can be quantified by (Giles et al., 2012). tion speeds for salinity anomalies the AO Index, the first empirical orthog- in the Northwest Atlantic vary from onal function (EOF) of the Northern 2. A sequential t-test analysis of regime 2–13 cm s–1, with lower values on the Hemisphere’s winter sea level pressure shifts (STARS; Rodionov, 2004) was shelf closer to the coast and higher val- field from 20°N to the pole (Thompson applied to each of the time series in ues along the shelf-slope break (Belkin, and Wallace, 1998). The Arctic Ocean Figure 1. For analyses of decadal-scale 2004; Sundby and Drinkwater, 2007; Oscillation (AOO) Index quantifies regime shifts, cut-off lengths of L = 5 Bisagni et al., 2009). Assuming an advec- the simulated sea-surface height gradi- and L = 10 years were tested. An L of five tive speed of 4 cm s–1, a parcel of low- ent forced by observed winds near the years better fit the AO Index and AOO salinity water would travel 1,261 km yr –1, center of the Arctic Basin; it provides a Index time series; an L of 10 years better and therefore the travel time between measure of geostrophic circulation in the fit all other time series. Statistically sig- the Canadian Arctic Archipelago and Beaufort Gyre, with positive (negative) nificant regime shifts were detected in all Georges Bank would be ~ 4 years. values corresponding to anticyclonic time series at p = 0.05. The 1996 regime (cyclonic) circulation (Proshutinsky and shift in the AO Index was only found 5. The Arctic Dipole Anomaly is an Johnson, 1997; Dukhovskoy et al., 2006; to be significant at p = 0.10. STARS atmospheric pressure pattern character- McLaughlin et al., 2011). The associa- was applied conservatively when gaps ized by high pressure above the North tion between Beaufort Gyre circulation, appeared in the time-series data, with American Arctic and low pressure above as measured by the AOO Index, and the regimes only indicated at L/2 before such the Eurasian Arctic. The Arctic Dipole generation of Great Salinity Anomalies gaps and L/2 after such gaps. Anomaly favors winds that generate (GSAs) in the North Atlantic has been a meridional transport of sea ice and relatively consistent since the 1960s. 3. The term Great Salinity Anomaly upper ocean waters across the Arctic The association between atmospheric (GSA) originally referred to the major Ocean and into the North Atlantic’s circulation in the Arctic, as measured pulse of low-salinity water entering the Greenland Sea through Fram Strait (Wu by the AO Index, and the generation of North Atlantic from the Arctic Ocean et al., 2006; Wang et al., 2009). GSAs in the North Atlantic, has changed during the late 1960s. Subsequently, dramatically since 1980. Prior to 1980, the term has been applied to similar 6. Individual time series of (a) Centro- the correlation between the AO Index events occurring during the 1980s and pages typicus, (b) Metridia lucens, and the AOO Index was not significant. 1990s (Belkin et al. 1998; Belkin 2004). (c) Oithona spp., and (d) Pseudocalanus After 1980, it became strongly nega- Three GSAs have been recognized in spp. abundance index values used in a tive. Dukhovskoy et al. (2006) suggest the literature (1970s GSA, 1980s GSA, principal component analysis to define that the abrupt switch may be related 1990s GSA), each with its own distinc- the Small Copepod Abundance Index to either insufficient observational data tive characteristics (Belkin 2004). All (Figure TN1). Each time series corre- before the International Arctic Buoy of these GSAs appear to have resulted sponds to the annual abundance anom- Program began in 1978 or a change in primarily from the export of ice and/ aly for late copepodites of each species the Atlantic’s influence over the Arctic, or low-salinity liquid water from the as determined from Gulf of Maine con- with a weaker Atlantic influence associ- Arctic Ocean to the North Atlantic tinuous plankton recorder survey data. ated with a reduced correlation between via either Fram Strait or the Canadian Positive values of indices are shaded in the AO and AOO Indices. Another Arctic Archipelago. red; negative values are shaded in blue. contributing factor may be the increased Solid black lines show regime shifts significant at the p 0.05 level.

1 7. Unusual atmosphere-ocean-cryo- freshwater in the Arctic Ocean served catastrophic reduction of sea ice extent sphere interactions have been observed to maintain the gyre’s anticyclonic observed in the Arctic Ocean. During in the Arctic since 2005 (see http://www. circulation despite countervailing 2008, the winter circulation was strongly whoi.edu/beaufortgyre/index.html, atmospheric winds. anticyclonic, but summer circulation was http://www.arctic.noaa.gov/reportcard/, During 2009, the annual AOO Index unusual with a relatively pronounced http://www.arctic.noaa.gov/future/ shifted to negative (cyclonic), with the Beaufort Gyre and a strong cyclonic index.html). During 2007 and 2008, the Beaufort Gyre significantly reduced circulation cell north of the Laptev Sea. annual AOO Index was strongly positive in strength and the Transpolar Drift During 2009, the system reversed rela- (anticyclonic) despite positive (cyclonic) becoming negligible. This was the first tive to seasonal climatology, being anti- values of the AO Index. Morison et al. cyclonic AOO Index observed since cyclonic during summer and cyclonic (2012) suggest that enhanced cyclonic 1997. The anticyclonic circulation during winter. These ocean circulation circulation on the Eurasian side of the regime that persisted from 1997–2008 patterns significantly influenced sea-ice Arctic Ocean may explain this unusual lasted 12 years rather than the typical extent as well as ocean freshwater and behavior. According to their explanation, five to eight years. The climatological heat content during 2008 and 2009. this recently enhanced cyclonic circula- seasonality of Arctic Ocean circulation is These changes feed back into the atmo- tion freshened the Canadian Basin by anticyclonic during winter and cyclonic sphere and may have long-term impacts transporting Eurasian river runoff east- during summer. Since 2007, this season- on the teleconnections between the ward along the Russian coast and inject- ality has shifted dramatically. During Arctic and lower latitudes (Overland and ing it across the Chukchi Borderland 2007, both summer and winter circula- Wang, 2010; Overland, 2011). into the Beaufort Gyre. By freshening tions were strongly anticyclonic, with the the Beaufort Gyre, this redistribution of summer conditions contributing to the

a c

b d

Figure TN1. Individual time series of (a) Centropages typicus, (b) Metridia lucens, (c) Oithona spp., and (d) Pseudocalanus spp. abundance index values. Positive values of indices above the climatological means are shaded in red; negative values below the climatological means are shaded in blue. Solid black lines show regime shifts significant at p = 0.05.