Arctic cyclone water vapor isotopes support past sea ice retreat recorded in Greenland ice

Abstract

Rapid Arctic warming is associated with important water cycle changes: sea ice loss, increasing atmospheric humidity, permafrost thaw, and water-induced ecosystem changes. Understanding these complex modern processes is critical to interpreting past hydrologic changes preserved in paleoclimate records and predicting future Arctic changes. Cyclones are a prevalent Arctic feature and water vapor isotope ratios during these events provide insights into modern hydrologic processes that help explain past changes to the Arctic water cycle. Here we present continuous measurements of water vapor isotope ratios (δ18O, δ2H, d-excess) in Arctic Alaska from a 2013 cyclone. This cyclone resulted in a sharp d-excess decrease and disproportional δ18O enrichment, indicative of a higher humidity open Arctic Ocean water vapor source. Past transitions to warmer climates inferred from Greenland ice core records also reveal sharp decreases in d-excess, hypothesized to represent reduced sea ice extent and an increase in oceanic moisture source to Greenland Ice Sheet precipitation. Thus, measurements of water vapor isotope ratios during an Arctic cyclone provide a critical processed-based explanation, and the first direct confirmation, of relationships previously assumed to govern water isotope ratios during sea ice retreat and increased input of northern ocean moisture into the Arctic water cycle.

Synoptic and Mesoscale Mechanisms Drive Winter Precipitation δ18O/δ2H in South‐Central Alaska

“…For example, winter is characterized by the lowest δ 18 O P /δ 2 H P and highest d‐excess values, as well as the largest proportion of trajectories originating in the Arctic (~40%, Figure a). Similar relationships were observed in the northern interior of Alaska (Klein et al, ) and central Aleutian Islands (Bailey et al, ) where precipitating air masses from the Arctic bring water vapor and precipitation that has relatively low δ 18 O and high d‐excess values. Alternatively, prevailing southerly storm tracks entrain warm 18 O‐enriched water vapor from lower latitude regions (i.e., the Pacific), and in these cases precipitation was found to have relatively high δ 18 O P /δ 2 H P and low d‐excess values (Bailey et al, ; Klein et al, ).…”

“…However, there is no significant correlation between δ 18 O P and recorded precipitation amount ( r 2 = 0.01, p = 0.18, n = 332), and local SAT explains only ~30% of variability in the δ 18 O P data ( r 2 = 0.33, p < 0.01, n = 332) with a temperature‐δ 18 O slope of 0.31‰/°C (Figure S1). This regression is similar to precipitation data from northern Alaska that exhibit a temperature‐δ 18 O P slope of 0.35‰/°C (Klein et al, ). Based on these observations, we propose a regional temperature‐δ 18 O P relationship of ~0.33‰/°C to be more appropriate for mainland Alaska than the global spatial average of 0.67‰/°C (Dansgaard, ).…”

How does sea ice influence &lt;i&gt;δ&lt;/i&gt;&lt;sup&gt;18&lt;/sup&gt;O of Arctic precipitation?

“…7), it is speculated that the perturbation in the isotopic composition are caused by changes in the contribution from local moisture sources. ice changes on the isotopic composition of moisture (Klein et al, 2015;Kopec et al, 2016). Changes in evaporation of local ocean water have also been suggested by modelling studies as important for sea ice induced changes in δ 18 O p (Sime et al, 2013;Noone, 2004).…”

Influence of sea ice on Arctic precipitation

“…We partition the two proportions, using the precipitation deuterium excess (d-excess, defined as d = δD − 8δ 18 O atomic ratios, respectively, from those of the standard mean ocean water), which is an indicator of moisture source conditions, principally the sea surface temperature (SST) and relative humidity (RH) (11)(12)(13). Moisture from subtropical regions has high d-excess values, indicative of relatively high SST and low RH at the source, whereas locally evaporated Arctic moisture has low d-excess values (14), indicating low SST and high RH. We hypothesize that precipitation d-excess is positively associated with sea ice area as a consequence of increasing local evaporation and thus increasing proportion of Arctic-sourced moisture with reduction of sea ice.…”