Insight into the sulfur cycle in the Baltic Sea surface sediments based on sulfur isotope records

Abstract

This thesis explores the sulfur cycle in the surface sediments of the Northern Baltic Sea, focusing on the isotopic composition of reduced sulfur. Additionally, the work includes setting up and validating an extraction line for acid volatile sulfide (AVS) and chromium reducible sulfur (CRS) at the University of Tartu. The extraction line proved effective for extracting sulfur species for isotope analysis but requires further improvements for achieving quantitative recoveries. Isotopic analyses of AVS and pyrite sulfur from three stations revealed significant differences in δ34S values despite similar sediment composition. This study suggests that the differences are linked to depositional conditions such as water depth, sedimentation rate, and redox state that create variabilities in system openness. The findings highlight the complexity of sulfur cycling and the importance of integrating depositional context and geochemical data to interpret isotopic signals in marine sediments.