Thin-sections of marine bivalve shells: a window to environmental reconstructions on daily scale?

• Main Author: von Leesen, Gotje
• Format: Thesis
• Language: unknown
• Published: 2014
• Subjects: Arctica islandica; Ocean quahog
• Online Access: https://epic.awi.de/id/eprint/37098/; https://epic.awi.de/id/eprint/37098/1/Bachelorarbeit_Gotje_Druckversion_klein.pdf; https://hdl.handle.net/10013/epic.44817; https://hdl.handle.net/10013/epic.44817.d001

“Bioarchives” are organisms, which form hard parts over the course of their lifetime that remain even after the death of the organism. Environmental conditions prevailed during the lifetime of the bioarchives can be approximated from anatomical, morphological and geochemical properties on the shell. For instance, shell growth rates constitute a “proxy” of general living conditions, oxygen isotope ratios (δ18O) are an established proxy of water temperature, and shell content of heavy metals or of organic constituents can be indicative specific pollution histories. Due to their high resolution, bivalve shells are well suited for sclerochronological studies. Generally, this science focuses on growth rates and chemical properties of hard parts. The ocean quahog Arctica islandica is suited as a bioarchive due to its broad geographic distribution and longevity. This study looks at growth patterns in the shells of the bivalve A. islandica (marine) and Unio sp. (freshwater). The objective was to establish standard procedures for shell preparation to visualize shell increments formed on a daily basis (“microincrements”). In order to visualize microincrements thin-sections of the marine bivalve A. islandica and the freshwater bivalve Unio sp. were prepared. Therefore, different attempts for embedding, etching, bleaching and visualization were tested. Microincrements are visible in thin-sections of both genera. The microincrements of the freshwater mussel Unio sp. are significantly smaller (1.5 μm on average) than those of A. islandica (12.5 μm on average). However, microincrements in Unio sp. are more easily recognizable and can be measured consecutively over a range of more than one year. The visualization of microincrements in A. islandica remained more challenging and therefore additional attempts such as bleaching, etching and additional visualization techniques were tested for their potential to improve the visualization of microincrements. The visualization of microincrements in A. islandica still needs further ...