Evidence of deuterium excess in water vapor as an indicator of ocean surface conditions

Abstract

[1] Stable isotopes of water are important climatic tracers used to understand atmospheric moisture cycling and to reconstruct paleoclimate. The combined use of hydrogen and oxygen isotopes in water provides an additional parameter, deuterium excess (d), which might reflect ocean surface conditions in moisture source regions for precipitation. The d records from polar ice cores covering glacial-interglacial cycles were used to reconstruct ocean surface temperatures at the moisture source, enabling elimination of source effects from the conventional isotope thermometer. However, observations of the essential relationship between d in vapor and ocean surface conditions are very limited. To date, theoretical values predicted using simple and atmospheric general circulation models (GCM) have not been validated against the data. Here, we show the isotope ratios of atmospheric water vapor near the ocean surface in middle and high latitudes of the Southern Ocean. Our observations show that d negatively correlates with relative humidity (h) above the ocean and correlates with sea surface temperature (SST). Despite the fact that the GCMs would underestimate the absolute value of observed d, the observations and simulation results are consistent for slopes between d versus h and d versus SST, suggesting that d is a reliable index to h and SST over the ocean surface.

The influence of the synoptic regime on stable water isotopes in precipitation at Dome C, East Antarctica

“…No correlation was found between observed deuterium excess and relative humidity at the estimated moisture source, which is contradictory to measurements by Uemura et al (2008) and Steen-Larsen et al (2014). Whether this has general physical reasons or is due to the fact that we studied individual events or to errors in moisture source estimation cannot be determined with the given data set.…”

Hydrogen and oxygen isotopic compositions of water vapor over the Bay of Bengal during monsoon

“…Though this leads to a systematic bias in predicting the vapor isotopic values [Jouzel et al, 1996], the relationship between h and d-excess is indeed observed in the marine vapor over the Southern Ocean [Uemura et al, 2008]. This relation is yet to be verified in the tropical oceans, a major moisture source for the global hydrological cycle.…”

Synoptic scale controls on the δ18O in precipitation across Beringia

“…Specifically, high d-excess values arise when there is insufficient time for vapor to equilibrate between the saturated ocean surface layer and the subsaturated atmosphere [e.g., Pfahl and Sodemann, 2014]. Evaporated moisture entrained in the Arctic (as opposed to Pacific) is subject to such conditions, whereby large-humidity gradients between the ocean surface and the dry atmosphere above-particularly at the sea ice margin [e.g., Kurita, 2011]-will lead to strong nonequilibrium (kinetic) fractionation and an evaporate characterized by relatively high d-excess and low δ 18 O [e.g., Gat et al, 2003;Uemura et al, 2008;Pfahl and Sodemann, 2014]. Furthermore, Adak receives increased snowfall during months with Arctic-derived moisture, and this will also be characterized by high d-excess due to nonequilibrium condensation during ice particle growth [Jouzel and Merlivat, 1984].…”