Compilation of a database of Holocene nearshore marine mollusk shell geochemistry from the California Current System

Abstract

Abstract. The shells of marine invertebrates can serve as high-resolution records of oceanographic and atmospheric change through time. In particular, oxygen and carbon isotope analyses of nearshore marine calcifiers that grow by accretion over their lifespans provide seasonal records of environmental and oceanographic conditions. Archaeological shell middens generated by Indigenous communities along the northwest coast of North America contain shells harvested over multiple seasons for millennia. These shell middens, as well as analyses of archival and modern shells, have the potential to provide multi-site, seasonal archives of nearshore conditions throughout the Holocene. A significant volume of oxygen and carbon isotope data from archaeological shells exist, yet they are separately published in archaeological, geochemical, and paleoceanographic journals and have not been comprehensively analyzed to examine oceanographic change over time. Here, we compiled a database of previously published oxygen and carbon isotope data from archaeological, archival, and modern marine mollusks from the California Current System (North American coast of the northeast Pacific, 32 to 55∘ N). This database includes oxygen and carbon isotope data from 598 modern, archaeological, and sub-fossil shells from 8880 years before present (BP) to the present, from which there are 4917 total δ13C and 7366 total δ18O measurements. Shell dating and sampling strategies vary among studies (1–345 samples per shell, mean 44.7 samples per shell) and vary significantly by journal discipline. Data are from various bivalves and gastropod species, with Mytilus spp. being the most commonly analyzed taxon. This novel database can be used to investigate changes in nearshore sea surface conditions including warm–cool oscillations, heat waves, and upwelling intensity, and it provides nearshore calcium carbonate δ13C and δ18O values that can be compared to the vast collections of offshore foraminiferal calcium carbonate δ13C and δ18O data from marine sediment cores. By utilizing previously published geochemical data from midden and museum shells rather than sampling new specimens, future scientific research can reduce or omit the alteration or destruction of culturally valued specimens and sites. The dataset is publicly available through PANGAEA at https://doi.org/10.1594/PANGAEA.941373 (Palmer et al., 2021).