Isotopic signals (18O, 2H, 3H) of six major rivers draining the pan-Arctic watershed

We present the results of a 4-year collaborative sampling effort that measured delta O-18, delta H-2 values and H-3 activities in the six largest Arctic rivers (the Ob, Yenisey, Lena, Kolyma, Yukon and Mackenzie). Using consistent sampling and data processing protocols, these isotopic measurements provide the best available d2H and 3H estimates for freshwater fluxes from the pan-Arctic watershed to the Arctic Ocean and adjacent seas, which complements previous efforts with d18O and other tracers. Flow-weighted annual d2H values vary from -113.3% to -171.4% among rivers. Annual 3H fluxes vary from 0.68 g to 4.12 g among basins. The integration of conventional hydrological and landscape observations with stable water isotope signals, and estimation of areal yield of 3H provide useful insights for understanding water sources, mixing and evaporation losses in these river basins. For example, an inverse correlation between the slope of the delta O-18-delta H-2 relation and wetland extent indicates that wetlands play comparatively important roles affecting evaporation losses in the Yukon and Mackenzie basins. Tritium areal yields (ranging from 0.760 to 1.695 10(-6) g/km(2) per year) are found to be positively correlated with permafrost coverage within the studied drainage basins. Isotope-discharge relationships demonstrate both linear and nonlinear response patterns, which highlights the complexity of hydrological processes in large Arctic river basins. These isotope observations and their relationship to discharge and landscape features indicate that basin-specific characteristics significantly influence hydrological processes in the pan-Arctic watershed.