Large-scale temperature and salinity changes in the upper Canadian Basin of the Arctic Ocean at a time of a drastic Arctic Oscillation inversion

摘要

Between 2008 and 2010, the Arctic Oscillation index over Arctic regionsshifted from positive values corresponding to more cyclonic conditionsprevailing during the 4th International Polar Year (IPY) period(2007–2008) to extremely negative values corresponding to strong anticyclonicconditions in 2010. In this context, we investigated the recent large-scaleevolution of the upper western Arctic Ocean, based on temperature and salinitysummertime observations collected during icebreaker campaigns and fromice-tethered profilers (ITPs) drifting across the region in 2008 and 2010.Particularly, we focused on (1) the freshwater content which was extensivelystudied during previous years, (2) the near-surface temperature maximum dueto incoming solar radiation, and (3) the water masses advected from thePacific Ocean into the Arctic Ocean. The observations revealed a freshwatercontent change in the Canadian Basin during this time period. South of80° N, the freshwater content increased, while north of80° N, less freshening occurred in 2010 compared to 2008. This wasmore likely due to the strong anticyclonicity characteristic of a low AOindex mode that enhanced both a wind-generated Ekman pumping in the BeaufortGyre and a possible diversion of the Siberian River runoff toward theEurasian Basin at the same time. The near-surface temperature maximum due toincoming solar radiation was almost 1 °C colder in the southernCanada Basin (south of 75° N) in 2010 compared to 2008, whichcontrasted with the positive trend observed during previous years. This wasmore likely due to higher summer sea ice concentration in 2010 compared to2008 in that region, and surface albedo feedback reflecting more sunradiation back in space. The Pacific water (PaW) was also subjected to strongspatial and temporal variability between 2008 and 2010. In the Canada Basin,both summer and winter PaW signatures were stronger between 75° N and80° N. This was more likely due to a strong recirculation within theBeaufort Gyre. In contrast, south of 75° N, the cooling and warmingof the summer and winter PaW, respectively, suggest that either the PaW wasless present in 2010 than in 2008 in this region, and/or the PaW was older in2010 than in 2008. In addition, in the vicinity of the Chukchi Sea, bothsummer and winter PaW were significantly warmer in 2010 than in 2008, as aconsequence of a general warming trend of the PaW entering in the deep ArcticOcean as of 2008.