Deuterium excess in marine water vapor: Dependency on relative humidity and surface wind speed during evaporation

Abstract

We provide the first continuous measurements of isotopic composition (δD and δ 18 O) of water vapor over the subtropical Eastern North Atlantic Ocean from mid-August to mid-September 2012. The ship was located mostly around 26°N, 35°W where evaporation exceeded by far precipitation and water vapor at 20 m largely originated from surface evaporation. The only large deviations from that occurred during a 2 day period in the vicinity of a weak low-pressure system. The continuous measurements were used to investigate deuterium excess (d-excess) relation to evaporation. During 25 days d-excess was negatively correlated with relative humidity (r 2 = 0.89). Moreover, d-excess estimated in an evaporative model with a closure assumption reproduced most of the observed variability. From these observations, the d-excess parameter seems to be a good indicator of evaporative conditions. We also conclude that in this region, d-excess into the marine boundary layer is less affected by mixing with the free troposphere than the isotopic composition. From our data, the transition from smooth to rough regime at the ocean surface is associated with a d-excess decrease of 5‰, which suggests the importance of the ocean surface roughness in controlling d-excess in this region.

Airborne in situ vertical profiling of HDO / H<sub>2</sub><sup>16</sup>O in the subtropical troposphere during the MUSICA remote sensing validation campaign

“…These measurements were taken at an altitude of less then 440 m above the ocean, and they are around 20 ‰ above the Rayleigh model. The elevated δD may be due to the evaporation of a fraction of sea spray into the lower atmosphere, a process suggested, e.g., by Benetti et al (2014).…”

“…Around the Canary Islands, the ocean water has δD ow ≈ +7 ‰ w.r.t. VSMOW (Benetti et al, 2014). The sea surface temperature (SST), which is used to derive the initial isotope fractionation during evaporation, was around 22.5 • C (NOAA_OI_SST_V2 data, http://www.esrl.…”

“…If the droplets evaporate (even partially), δD of the vapor becomes less negative (Gat et al, 2003;Benetti et al, 2014). We can estimate the fraction F of sea spray that evaporated without fractionation and mixed with evaporated ocean water by solving…”

Vapor hydrogen and oxygen isotopes reflect water of combustion in the urban atmosphere

“…We show that water vapor deuterium excess (d = δ 2 H -8 × δ 18 O) closely tracks changes in CO 2 through inversion events and across a daily cycle dominated by patterns of human activity. Deuterium excess reflects deviations in the coupled H and O isotopic compositions of water from a covariant trend established by equilibrium phase-change reactions in the atmosphere, and has previously been used to diagnose vapor source region conditions, nonequilibrium processes, and vertical mixing (18)(19)(20)(21). We demonstrate that combustion-derived water vapor is characterized by a distinctive d value due to its unique mode of production, illustrate that this strong signal is detectible and can be used to quantify the concentration of combustion-derived vapor in the SLC wintertime atmosphere, and demonstrate congruence between these estimates and those derived from a mass-balance model forced by meteorological and emissions data.…”

Fuel Production from Seawater and Fuel Cells Using Seawater

“…[61] The near-surface relative humidity over the oceans is fairly constant between 75 and 90 %w ith only minor variation by seasono rt ime of day. [62,63] Marine solar water vapor electrolysis can indirectly split seawater without any water purification process. [63] The electrolyzer consists of two stainless steel grids for the anode andt he cathode, two carbon To ray paper sheets as gas-diffusion layers, and one membrane electrode assembly (MEA)w ith catalystp articles (Pt/C) on either side of a sulfonated polytetrafluoroethylene (Nafion) proton-exchange membrane ( Figure 5).…”