Modification of the Laptev Sea Freshened Shelf Waters based on Isotope and Salinity Relations

Abstract—This work addresses the problem of estimating the contribution of river runoff in seawaters of the Arctic shelf, where freshening is accompanied by intense freezing and melting of desalinated water. The water mixing–modification model was proposed with correction for the formation of sea ice from desalinated waters on the shelf. The model was applied to the interpretation of data obtained during cruises 63 and 69 of the R/VAkademik Mstislav Keldysh (2015 and 2017). Two water sources were established for the Laptev Sea shelf waters in the studied area: Atlantic and Lena waters. However, waters in this shelf zone were modified, i.e., have higher salinity than that inferred from mixing of two established components. The presence of modified waters supplying from the Laptev Sea shelf is traced in the zone of continental slope. Desalination in this zone reaches 15–27%, spans depths up to 20 m, and is practically absent at depths more than 50 m. A mixing–modification model was developed in order to calculate the fraction of river runoff in modified waters. Based on obtained data, the fraction of river runoff was determined using the proposed model and generally accepted model of three-component mixing (Ostlund and Hut, 1984). The comparison of results obtained using both the models for the Laptev Sea shelf showed that the application of three-component mixing to modified waters yields overestimated values (up to 20%) for the contribution of river runoff. The criterion was proposed to decide which model is better for each sample. Using such complex approach, we avoid obtaining erroneous and negative values for end-member fractions and overestimated values for contribution of freshwater component.