Paired bulk organic and individual amino acid δ 15 N analyses of bivalve shell periostracum: A paleoceanographic proxy for water source variability and nitrogen cycling processes
Nina M. Whitney Beverly Johnson Philip Dostie Katherine Luzier Alan D. Wanamaker
Developing high-resolution, well-dated, marine proxies of environmental, climatic, and oceanographic conditions is critical in order to advance our understanding of the ocean's role in the global clim..
Developing high-resolution, well-dated, marine proxies of environmental, climatic, and oceanographic conditions is critical in order to advance our understanding of the ocean's role in the global climate system. While some work has investigated bulk and compound specific stable nitrogen isotope (δ 15 N) values in bivalve shells as proxies for environmental variability, the small concentrations of nitrogen found in the organic matrix of the shell calcium carbonate (hereafter carbonate) makes developing high resolution records challenging. This study investigates the potential of using the bulk and amino acid δ 15 N values of bivalve periostracum, the protein layer on the outside of the shell, as a proxy archive of nitrogen cycling processes and water source variability. Bulk δ 15 N values were measured on the periostracum, carbonate, and adductor muscle of Arctica islandica shells collected in the Gulf of Maine. Increased variability of isotopic values across growth lines compared to along growth lines support mechanistic reasoning based on growth processes that periostracum is recording changes in δ 15 N values over the course of the clam's lifetime (up to 500 years). In addition, the statistically significant relationship between periostracum δ 15 N values and contemporaneous carbonate δ 15 N values of the same shell (r = 0.82, p