Modeling of the isotope (δ18O, δ2H) composition and salinity of the seawater surface layer in polar regions: Application for the East and European arctic

Abstract

The surface sea water salinity and isotope (δ¹⁸O, δ²H) composition in polar regions are determined by the balance between freshening and freezing-related processes. Due to sea ice formation and its melting, the relation between the salinity and δ¹⁸O(δ²H) values does not correspond entirely to an additive process. We propose the dynamic model of surface layer (DMSL), which considers the fluxes corresponding to the freshening, freezing, and sea ice melting in order to describe the δ¹⁸O(δ²H)–salinity and δ¹⁸O–δ²H relations in Arctic seawater. The DMSL shows that the slope in the δ–salinity space is a complex function of melting and freezing fluxes, freshwater flux, salinity, and isotope composition of marine and freshwater endmembers. The model can be applied to salinity and isotope signatures both for any whole water region and for single water samples. The testing of the DMSL was done for water areas covered with different freezing–melting activity, located both in shelf areas influenced of continental runoff and in areas isolated from it. The data used for test calculations were obtained for surface (0–15 m) seawater collected in the Eastern and European Arctic in 2017, 2018, and 2021 (70°–82.7° N, and −4° W to 168° E) at the end of ice-free seasons. The calculations show that the model is capable of adequately estimating both the isotope signature of fresh water and the ratio of the main fluxes that form the surface layer: freshening, modification, and the contribution from melting sea ice.