Circulation of Pacific Winter Water in the Western Arctic Ocean

Pacific Winter Water (PWW) enters the western Arctic Ocean from the Chukchi Sea; however, the physical mechanisms that regulate its circulation within the deep basin are still not clear. Here, we investigate the interannual variability of PWW with a comprehensive data set over a decade. We quantify the thickening and expansion of the PWW layer during 2002–2016, as well as its changing pathway. The total volume of PWW in the Beaufort Gyre (BG) region is estimated to have increased from 3.48 ± 0.04 × 1014 m3 during 2002–2006 to 4.11 ± 0.02 × 1014 m3 during 2011–2016, an increase of 18%. We find that the deepening rate of the lower bound of PWW is almost double that of its upper bound in the northern Canada Basin, a result of lateral flux convergence of PWW (via lateral advection of PWW from the Chukchi Borderland) in addition to the Ekman pumping. In particular, of the 70‐m deepening of PWW at its lower bound observed over 2003–2011 in the northwestern basin, 43% resulted from lateral flux convergence. We also find a redistribution of PWW in recent years toward the Chukchi Borderland associated with the wind‐driven spin‐up and westward shift of the BG. Finally, we hypothesize that a recently observed increase of lower halocline eddies in the BG might be explained by this redistribution, through a compression mechanism over the Chukchi Borderland. Plain Language Summary Pacific Winter Water (PWW) is a deeper freshwater source via subduction in contrast to the wind‐driven Ekman convergence of freshwater in the surface Ekman layer of the western Arctic Ocean. It supplies the western Arctic Ocean with acidifying water. Our study reveals a redistribution of PWW associated with the wind‐driven spin‐up of Beaufort Gyre. The lateral advection of PWW from the Chukchi Borderland to the northern Canada Basin plays an important role in the deepening of PWW lower bound at the edge of Beaufort Gyre. In addition, the total volume of PWW has increased about 18% over the years 2002–2016. Our findings provide an important implication not only for the physical oceanographer but also for the marine chemists and biologists. Key Points PWW is a deeper freshwater source in contrast to the wind‐driven Ekman convergence of freshwater in the surface layer of the western Arctic An anticyclonic pathway of PWW is identified from hydrographic and mooring data over the years 2002‐2016 The upper and lower bounds of PWW show a significantly different deepening rate at the edge of the Beaufo