Tracking the history of Baltic Sea hypoxia with bivalve shells

• Main Author: Huang, Xizhi
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Johannes Gutenberg-Universität Mainz 2024
• Subjects: ddc:333.7; ddc:500; ddc:550; ddc:560; Arctica islandica; Ocean quahog
• Online Access: https://openscience.ub.uni-mainz.de/handle/20.500.12030/10292; https://hdl.handle.net/20.500.12030/10292; https://doi.org/10.25358/openscience-10274

Deoxygenation is a growing issue in global open oceans and coastal waters leading to hypoxia, of which the Baltic Sea is one of the largest oxygen-deficient settings in the world. As a model region, understanding the past occurrence of Baltic Sea hypoxia is crucial for informing present- day coastal perturbations and developing future mitigation strategies. To date, reconstructing the history of hypoxia in the Baltic Sea is almost exclusively on proxies archived in sediment cores, which have low temporal resolution and poor dating control, limiting the ability to provide detail information on dissolved oxygen (DO) variability and hypoxic events. To reliably predict the DO development in the Baltic Sea, it is of paramount important to identify the leading to oxygen depletion based on an accurate understanding of historical trends in DO. Hence, developing temporally well-constrained and highly resolved DO proxy archives that can overcome the limitations of sedimentary records is imperative. The shells of bivalve mollusks may fulfill this task as they can function as precisely dated and seasonally to interannually resolved archives of environmental changes. Specifically, an redox-sensitive element such as Mn has the potential to be used as a surrogate for DO. However, it remains a challenge to quantitatively interpret the environmental signatures from elemental impurities in bivalve shells. Before shell Mn/Ca values can be used to quantify DO concentrations, this proxy needs to be calibrated. The present study was based on shell materials of long-lived bivalve specimens and adopted sclerochronological techniques (Chapter 2). The results of this project comprise four manuscripts published in international, peer-reviewed scientific journals. In Chapter 3, the ocean quahog Arctica islandica, an extremely long-lived and low- oxygen adapted bivalve species commonly used for paleoclimate reconstructions, was studied. All specimens of A. islandica were collected alive at the same time from the Mecklenburg Bight, SW Baltic ...