Craig-Gordon model validation using observed meteorological parameters and measured stable isotope ratios in water vapor over the Southern Ocean
The stable isotopic composition of water vapor over the ocean is governed by the isotopic composition of surface water, ambient vapor isotopic composition, exchange and mixing processes at the water-air interface as well as the local meteorological conditions. In this study we present water vapor an...
| Main Authors: | , , , |
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| Format: | Text |
| Language: | English |
| Published: |
2019
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/acp-2019-950 https://www.atmos-chem-phys-discuss.net/acp-2019-950/ |
| Summary: | The stable isotopic composition of water vapor over the ocean is governed by the isotopic composition of surface water, ambient vapor isotopic composition, exchange and mixing processes at the water-air interface as well as the local meteorological conditions. In this study we present water vapor and surface water isotope ratios in samples collected across the latitudinal transect from Mauritius to Prydz Bay in the Antarctic coast. The samples were collected on-board the ocean research vessel SA Agulhas during the 9 th (Jan-2017) and 10 th (Dec-2017 to Jan-2018) Southern Ocean expeditions. The inter annual variability of the meteorological factors governing water vapor isotopic composition is explained. The parameters governing the isotopic composition of evaporation flux from the oceans can be considered separately or simultaneously in the Craig-Gordon (CG) models. The Traditional Craig-Gordon (TCG) (Craig and Gordon, 1965) and the Unified Craig-Gordon (UCG) (Gonfiantini et al., 2018) models were used to evaluate the isotopic composition of evaporation flux for the molecular diffusivity ratios suggested by Merlivat (1978) (MJ), Cappa et al. (2003) (CD) and Pfahl and Wernli (2009) (PW) and for different ocean surface conditions. We found that the UCG model with CD molecular diffusivity ratios where equal contribution from molecular and turbulent diffusion is the best match for our observations. By assigning the representative end member isotopic compositions and solving the two-component mixing model, a relative contribution from locally generated and advected moisture was calculated along the transect. Our results suggest varying contribution of advected westerly component with an increasing trend upto 65° S. Beyond 65° S, the proportion of Antarctic moisture was found to be increasing linearly towards the coast. |
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