Origin of Arctic water vapor during the ice-growth season

Abstract

[1] Recent extreme minima in Arctic summer sea ice extent have led to enhanced heat flux from the ocean to the atmosphere. This change may increase the humidity in Arctic air masses during the ice-growth season. Humidity increases may also be sustained by enhanced moisture transport into the Arctic and the relative influence of local- versus distant-moisture sources remains uncertain. Here we examined the predominant origin of Arctic water vapor during the ice-growth period, using water isotopologues (HDO, H218O) as tracers. An exploration of the isotopic evolution of surface water vapor in the Arctic Ocean found that isotopic values of moisture originating from the Arctic Ocean were characterized by higher d-excess values, a second-order isotopic parameter, than those of moisture originating from lower latitudes. These high d-excess values (>20‰) in Arctic-origin air masses were observed in mid-autumn. Subsequently, high d-excess values gradually decreased to the global average (d = 10) and disappeared in early winter, when sea ice covered a large part of the Arctic Ocean. This change suggests that the humidity source of Arctic air masses switches in early winter from locally driven to moisture transport from lower latitudes.