Hydrographic trends in Prince William Sound, Alaska, 1960–2016

Abstract

A five-decade time series of temperature and salinity profiles within Prince William Sound (PWS) and the immediately adjacent shelf was assembled from several archives and ongoing field programs, and augmented with archived SST observations. Observations matched with recent cool (2007–2013) and warm (2013-onward) periods in the region, and also showed an overall regional warming trend (~ 0.1 to 0.2°C decade−1) that matched long-term increases in heat transport to the surface ocean. A cooling and freshening trend (~ − 0.2°C decade−1 and 0.02 respectively) occurred in the near surface waters in some portions of PWS, particularly the northwestern margin, which is also the location of most of the ice mass in the region; discharge (estimated from other studies) has increased over time, suggesting that those patterns were due to increased meltwater inputs. Increases in salinity at depth were consistent with enhanced entrainment of deep water by estuarine circulations, and by enhanced deep water renewal caused by reductions in downwelling-favorable winds. As well as local-scale effects, temperature and salinity were positively cross correlated with large scale climate and lunar indexes at long lags (years to months), indicating the longer time scales of atmospheric and transport connections with the Gulf of Alaska. Estimates of mixed layer depths show a shoaling of the seasonal mixed layer over time by several meters, which may have implications for ecosystem productivity in the region.