Global climate is influenced by the Arctic hydrologic cycle, which is, in part, regulated by sea ice through its control on evaporation and precipitation. However, the quantitative link between precipitation and sea ice extent is poorly constrained. Here we present observational evidence for the response of precipitation to sea ice reduction and assess the sensitivity of the response. Changes in the proportion of moisture sourced from the Arctic with sea ice change in the Canadian Arctic and Greenland Sea regions over the past two decades are inferred from annually averaged deuterium excess (d-excess) measurements from six sites. Other influences on the Arctic hydrologic cycle, such as the strength of meridional transport, are assessed using the North Atlantic Oscillation index. We find that the independent, direct effect of sea ice on the increase of the percentage of Arctic sourced moisture (or Arctic moisture proportion, AMP) is 18.2 ± 4.6% and 10.8 ± 3.6%/100,000 km 2 sea ice lost for each region, respectively, corresponding to increases of 10.9 ± 2.8% and 2.7 ± 1.1%/1°C of warming in the vapor source regions. The moisture source changes likely result in increases of precipitation and changes in energy balance, creating significant uncertainty for climate predictions.water cycle | precipitation | sea ice | climate change | deuterium excess T here is increasing interest in the response of the Arctic hydrologic cycle to changing climate because of its potential to influence, or feedback to, future climate change. Modeling studies have identified enhanced transport of subtropical moisture to the Arctic as well as increased Arctic evaporation as potential mechanisms of augmentation of the water cycle (1-3). The enhanced hydrologic cycle may feedback to climate change either positively or negatively; both the sign and the magnitude are yet to be determined.Observational evidence for hydrological acceleration during the past few decades is limited. Direct measurement of precipitation is difficult in the Arctic because of its cold, windy environments (4). Despite these difficulties, increasing precipitation has been reported for some Arctic locations (5, 6), and it has been hypothesized that changes in sea ice extent may have significantly influenced precipitation both in the past (7) and today (8-10). We report a study of changes in the isotopic composition of precipitation to understand the larger-scale changes of the hydrologic cycle, focusing on moisture source changes. The objective of this work is to assess observationally the effect of sea ice and the moisture transport regime on Arctic precipitation from 1990 to 2012, using the isotopic composition of precipitation from six Arctic stations. In particular, we quantify how the fraction of the total Arctic precipitation that is sourced in the Arctic responds to the sea ice extent. We then use these empirically established sensitivities of precipitation isotope ratios to sea ice change to project potential future precipitation changes and to evaluate impacts of...

We present a study of the dynamics of small-scale (~100 km) atmospheric circulation in west Greenland which is dominated by interactions of marine and continental air masses. Water vapor concentration and isotopic ratios measured continuously over a 25 day period in Kangerlussuaq, Greenland were used to monitor the convergence of easterly katabatic winds and westerly sea breezes that form a front between the dry, isotopically depleted, glacial air mass and the moist, isotopically enriched, marine air mass. During the latter 16 days of the measurement period, an interval with no large-scale synoptic interference, the inland penetration of the sea breeze controlled the largest day-to-day humidity and vapor isotopic variations. Kangerlussuaq experienced sea breezes in the afternoon on 9 days, consistent with the long-term average of such occurrences on 56% of days in July and August. The inland position of the sea breeze front is controlled by the katabatic wind strength, which is stronger during times of reduced cloud coverage and/or higher-pressure gradient between the coast and the Greenland ice sheet. The position and movement of the front will likely respond to changes in the general atmospheric circulation and regional radiation balance resulting from global warming, which will, in turn, impact the local hydrological cycle and ecosystem processes.

The hydrogen and oxygen isotopic composition of ice cores from Summit, Greenland, has provided invaluable information about variations in past climate. However, interpretations of these isotopic data have been made despite a paucity of direct isotopic studies of Summit precipitation. We provide insight to such interpretations by examining the annual cycle of deuterium excess (d‐excess) in precipitation samples from Summit and by considering the climatic controls on the annual cycle. Precipitation was collected daily from July 2011 to September 2014 at heights of 1, 2, and 4 m. The isotopic composition of precipitation sampled at 4 m above the snow surface is free of contamination from blowing snow. Precipitation d‐excess is high in the summer and low in the winter, a pattern opposite to that found at most high‐latitude locations, where summer d‐excess is low relative to winter. Low winter d‐excess values at Summit can be explained by varying degrees of Rayleigh distillation of moisture sourced from isotopically similar marine sources. However, the observed summer d‐excess maximum at Summit is anomalously high compared with other Arctic locations, and we propose that this is due to high d‐excess moisture contributed by sublimation of surface snow on the Greenland Ice Sheet. We demonstrate the plausibility of this hypothesis through simple isotopic mass balance calculations, analyses of cloud heights, and back trajectories to identify moisture sources. We show that Rayleigh distillation, sublimation, and the phase of the d‐excess annual cycle are all important factors that should be considered in ice core d‐excess interpretations.

No abstract