Arctic Ocean Freshwater Changes Over the Past 100 Years and Their Causes

Using a vast collection of previously unsynthesized observational data, we demonstrate that over the 20th century the central Arctic Ocean became increasingly saltier with a rate of freshwater loss ~239km3 per decade. In contrast, long-term (1920-2003) freshwater content (FWC) trends over the Siberian shelf show general freshening tendency with a rate of ~29km3 per decade. These FWC trends are modulated by strong variability with sustained and widespread patterns. Associated with this variability, the FWC record shows two periods in the 1920-30s and in recent decades when the central Arctic Ocean was saltier and two periods in the earlier century and in the 1940-70s when it was fresher. Our analysis of potential causes for the recent central Arctic Ocean salinification suggests that the FWC anomalies generated on arctic shelves (including anomalies resulting from river discharge inputs) and those caused by net atmospheric precipitation were too small to trigger long-term FWC variations in the central Arctic Ocean; to the contrary, they tend to moderate the observed long-term central-basin FWC changes. Variability of the intermediate Atlantic Water did not have apparent impact on changes of the upper Arctic Ocean water masses. Our estimates suggest that ice production and sustained draining of freshwater from the Arctic Ocean in response to winds are the key contributors to the salinification of the upper Arctic Ocean over recent decades. Strength of the export of arctic ice and water controls the supply of Arctic fresh water to sub-polar basins while the intensity of the Arctic Ocean FWC anomalies is of less importance. Observational data demonstrate striking coherent long-term variations of the key Arctic climate parameters and strong coupling of long-term changes in the Arctic/North Atlantic climate system.