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Abstract. The shells of marine invertebrates can serve as high-resolution records ofoceanographic and atmospheric change through time. In particular, oxygen andcarbon isotope analyses of nearshore marine calcifiers that grow byaccretion over their lifespans provide seasonal records of environmental andoceanographic conditions. Archaeological shell middens generated byIndigenous communities along the northwest coast of North America containshells harvested over multiple seasons for millennia. These shell middens,as well as analyses of archival and modern shells, have the potential toprovide multi-site, seasonal archives of nearshore conditions throughout theHolocene. A significant volume of oxygen and carbon isotope data fromarchaeological shells exist, yet they are separately published in archaeological,geochemical, and paleoceanographic journals and have not been comprehensivelyanalyzed to examine oceanographic change over time. Here, we compiled adatabase of previously published oxygen and carbon isotope data fromarchaeological, archival, and modern marine mollusks from the CaliforniaCurrent System (North American coast of the northeast Pacific, 32 to55∘ N). This database includes oxygen and carbon isotope data from 598modern, archaeological, and sub-fossil shells from 8880 years before present(BP) to the present, from which there are 4917 total δ13C and7366 total δ18O measurements. Shell dating and samplingstrategies vary among studies (1–345 samples per shell, mean 44.7 samplesper shell) and vary significantly by journal discipline. Data are fromvarious bivalves and gastropod species, with Mytilus spp. being the most commonlyanalyzed taxon. This novel database can be used to investigate changes innearshore sea surface conditions including warm–cool oscillations, heatwaves, and upwelling intensity, and it provides nearshore calcium carbonateδ13C and δ18O values that can be compared to thevast collections of offshore foraminiferal calcium carbonate δ13C and δ18O data from marine sediment cores. Byutilizing previously published geochemical data from midden and museumshells rather than sampling new specimens, future scientific research canreduce or omit the alteration or destruction of culturally valued specimensand sites. The dataset is publicly available through PANGAEA athttps://doi.org/10.1594/PANGAEA.941373 (Palmer et al.,2021). 

Abstract. Microfossil assemblages provide valuable records to investigatevariability in continental margin biogeochemical cycles, including dynamicsof the oxygen minimum zone (OMZ). Analyses of modern assemblages acrossenvironmental gradients are necessary to understand relationships betweenassemblage characteristics and environmental factors. Five cores wereanalyzed from the San Diego margin (32∘42′00′′ N, 117∘30′00′′ W; 300–1175 m water depth) for core top benthic foraminiferalassemblages to understand relationships between community assemblages andspatial hydrographic gradients as well as for down-core benthic foraminiferalassemblages to identify changes in the OMZ through time. Comparisons ofbenthic foraminiferal assemblages from two size fractions (63–150 and>150 µm) exhibit similar trends across the spatial and environmental gradient or in some cases exhibit more pronouncedspatial trends in the >150 µm fraction. A range of speciesdiversity exists within the modern OMZ (1.910–2.586 H, Shannon index),suggesting that diversity is not driven by oxygenation alone. We identifytwo hypoxic-associated species (B. spissa and U. peregrina), one oxic-associated species (G. subglobosa) andone OMZ edge-associated species (B. argentea). Down-core analysis of indicator speciesreveals variability in the upper margin of the OMZ (528 m water depth) whilethe core of the OMZ (800 m) and below the OMZ (1175 m) remained stable inthe last 1.5 kyr. We document expansion of the upper margin of the OMZbeginning 400 BP on the San Diego margin that is synchronous with otherregional records of oxygenation.