| Summary: | Water isotopes (δ18O (delta-O-18) , δ2H (delta deuterium), deuterium-excess) are important tracers that help understand the changing Arctic water cycle and how Arctic sourced water can influence lower latitudes. We present simultaneous boundary layer water vapor and ocean water isotopes measured continuously from the western Arctic Ocean. Sea surface water isotopes vary between the shallower continental Chukchi Shelf and deeper Chukchi Borderlands waters. The Chukchi Borderlands surface waters are less saline than the Chukchi Shelf, as it is influenced by greater sea ice cover and contribution of sea ice melt to the surface freshwater component. This greater contribution of sea ice melt results in lower deuterium-excess (δ2H - 8*δ18O) surface water values in the deeper Chukchi Borderlands than on the shallower Chukchi Shelf. Additionally, the sea ice melt contributions to freshwater are less than river runoff, but freshwater from both sources decrease substantially below 70 meters depth in the Chukchi Borderlands. Our observed water isotope values provide the foundation for a remote sensing and machine learning based production of water isotope maps (isoscapes), which incorporate parameters that can influence ocean circulation and thus water isotopes (e.g., salinity, sea surface temperature, water depth). These isoscapes reveal unprecedented insight into the spatial complexity of Arctic water isotopes, including sharp gradients between sea water isotopes that are more representative of ocean dynamics. Additionally, the isoscapes reveal how the Anadyr Current and Alaska Coastal Current differentially influence water isotope characteristics in the Bering Sea and flow through the Bering Strait into the Arctic Ocean. These isoscapes can be improved in future iterations (e.g., with the availability of more spatially-continuous remotely sensed oceanic variables to use as additional predictors) and could become a useful tool for understanding the past, present, and future global water cycle as the Arctic experiences rapid changes that transport waters beyond the Arctic basin.
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