River freshwater flux to the Arctic ocean

Abstract

Various estimates of freshwater discharge to the Arctic Ocean with different methods and for different drainage areas have shown a good consistency in long-term mean runoff ranging from 200 mm/year to 226 mm/year. Most of the estimates are derived from available discharge measurements at the downstream gauging stations. According to the most recent assessment of the total discharge to the Arctic Ocean is approximately 4300 km3 year-1 and continental contributions to the river input into the Arctic Ocean for Asia, North America, and Europe are 55%, 28%, and 17%, respectively. The river flux to the Arctic Ocean has significantly changed with an increase of 210 km3 over 1936-2015 across Eurasia, and 36 km3 over 1964-2015 for northern Canada. These changes were especially pronounced during the last 30-years, associated with most intense warming of air temperature over the northern hemisphere and significant declines in sea ice extent over the Arctic Ocean. The significant increase in annual river flow is mainly due to increases in winter (60%) and spring (33%) discharge. Winter flows have a very consistent and significant increase throughout the Eurasian pan-Arctic. All six largest Eurasian Arctic rivers show a significant increase in winter river flows over the long-term period 1936-2015. Similar but less significant trends in winter and spring discharge were found for Canadian northern rivers. Seasonal discharge has been altered as the result of human activity, particularly reservoir regulation. Eliminating reservoir effect in the largest Arctic rivers of Yenisei, Lena, and Ob, using the hydrograph transformation model, show significant increase in annual discharge, i.e., increase in spring by 49%, winter by 31%, and summer-fall by 20%. These results are different from those obtained from the observational discharge data. Thus, for hydroclimatic analysis to understand possible changes in river flux to the Arctic Ocean, it is necessary to take into account human impact on the discharge regime and change. Sea surface salinity (SSS) links various components of the Arctic freshwater system, including river discharge. Analysis of remote sensed SSS data has shown that SSS distribution pattern in the Arctic Ocean during warm period is partly defined by river flux. There is a great potential of using remote sensing data for a better understanding of variability in the Arctic freshwater system.