Background
The authors say contemporary climate modeling "shows that an increased freshwater export from the Arctic Ocean into the northern North Atlantic could induce changes of the Atlantic meridional overturning circulation, which at the end would affect climate of the Northern Hemisphere," and, therefore, that "freshening of Arctic surface waters in general is found to be an alarming signal for global change (e.g., Arctic Climate Impact Assessment (ACIA), 2004)."  Hence, they evaluate the validity of this "alarming signal" assumption for the waters of the Kara Sea off the northern coast of Siberia between 73 and 77°N and 75 and 86°E.

What was done
Simstich et al. calculated 1996 to 2000 trends in the mean salinity of the whole Kara Sea (surface to bottom) by means of combined modeling and hydrographic data derived from measurements of temperature and salinity made with deep-sea thermometers, electrical salinity meters, and titration and conductivity-temperature-depth probes, as well as same-period bottom-water salinity trends based on oxygen and stable carbon isotope profiles derived from bivalve shells, which they say "reliably record all important aspects of the bottom water hydrography in the shallow southeastern Kara Sea."

What was learned
The group's research revealed that the mean salinity of the whole Kara Sea dropped by roughly 0.5 between 1996 and 2000.  However, the increase in river discharge over this period was deemed to be far below the range required to produce a widespread freshening of this magnitude.  As a result, Simstich et al. concluded that "an increased supply of river water to the Kara Sea can thus be ruled out as a single cause for the observed freshening."  Looking for other explanations, they found them in wind-driven phenomena, whereby over the period of their study "weakening of the prevailing southwesterly winds diminished the inflow of saline Atlantic-derived water from the Barents Sea through the Kara Strait in the southwest, and, additionally, reduced the export of river water toward the north and northeast into the Arctic basin," so that "saline Atlantic-derived water thus was replaced by freshwater, which was successively accumulated in the Kara Sea and accordingly imprinted on the stable isotope composition of the bivalve shells."

What it means
When all was said and done, Simstich et al. concluded that the salinity decrease in the Kara Sea during the 1990s "seems to be less the result of changes in the hydrologic cycle owing to greenhouse forcing than the result of natural variations in atmospheric pressure fields."  Once again, therefore, the "alarming signal" of CO2-induced global warming could not be convincingly identified where, according to model simulations and climate-alarmist claims, it is supposed to be most evident, i.e., in high northern latitudes.

Reference
Arctic Climate Impact Assessment (ACIA).  2004.  Impacts of a Warming Arctic: Arctic Climate Impact Assessment.  Cambridge University Press, New York, New York, USA.