Deconstructing Changes in the Strength of the Arctic Halocline with Transect Data from the Arctic Ocean Sections

There have been two major trans-Arctic scientific icebreaker cruises crossing the Central Arctic: the 1994 Arctic Ocean Sciences cruise aboard the Canadian Coast Guard's Louis S. St. Laurent, and the 2005 AOS cruise aboard the Swedish Polar Research Institute's Icebreaker Oden. The latter collected 53 full-depth CTD and bottle casts between Alaska and the Barents Sea. We present transects of hydrographic, nutrient and isotope tracers AOS 2005. Along the overlap of the two cruises, the expedition found a decrease in salinity in the upper waters of the Makarov Basin, leading to an increase in the strength of the Halocline there. We use oxygen isotope measurements, salinity and nutrient concentrations to attribute the change to a mixture of decreased sea-ice formation and increased concentrations of river runoff. The 2005 water mass analysis is also used to discuss some important differences in water-mass decomposition techniques, and important updates to the analysis of the 1994 isotope data are presented. Perhaps surprisingly, the change in sea-ice is responsible for less than 1/3 of the change, with the bulk of the anomaly attributable to increased focusing of meteoric water in the central Arctic.