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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...

[1] We use data from Global Network of Isotopes in Precipitation (GNIP) database to explore how the atmosphere's meridional circulation cells control the latitudinal and seasonal distribution of d 18O and d-excess in precipitation. We demonstrate that the atmospheric general circulation (AGC) cells determine variations of zonally averaged isotopic composition of meteoric water; the local isotopic minimum near the equator coincides with the intertropical convergence (ITC), and two maxima on either side of the ITC coincide with the subtropical highs (STHs). Both the ITC and STHs migrate cum sole, as part of the systematic annual migration of the meridional cells. This migratory circulation pattern controls the phase of the annual oscillation of the precipitation d 18 O. At latitudes equatorward of the STHs, d18 O reaches its maximum in the winter of the respective hemisphere and at higher latitudes in the summer. From the monthly latitudinal distribution of the vertical velocity at the 500-hPa level, we obtain the seasonal variations of the latitudinal positions of the subtropical moisture source regions and their climates. The sea surface temperature and relative humidity at the moisture source regions are used to predict seasonal changes of the d-excess of water vapor evaporated from the source regions. The GNIP data is consistent with the predicted phase of the d-excess. However, the observed magnitude of the seasonal oscillation is greater than the predicted values. This work provides a baseline for understanding the influence of subtropical moisture source regions and other climatological factors on the d-excess.

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