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Reconstructions of ancient ocean chemistry are largely based on geochemical proxies obtained from epicontinental seas. Mounting evidence suggests that these shallow inland seas were chemically distinct from the nearby open ocean, decoupling epicontinental records from broader ocean conditions. Here we use the isotope-enabled Community Earth System Model to evaluate the extent to which the oxygen isotopic composition of the late Carboniferous epicontinental sea, the North American Midcontinent Sea (NAMS), reflects the chemistry of its open-ocean sources and connect epicontinental isotope variability in the sea to large-scale ocean-atmosphere processes. Model results support estuarine-like circulation patterns demonstrated by past empirical studies and suggest that orographic runoff produced decreases in surface seawater δ18O (δ18Ow) of up to ∼3between the NAMS and the bordering ocean. Simulated sea surface temperatures are relatively constant across the sea and broadly reproduced from proxy-based δ18O paleotemperatures for which model-based values of epicontinental δ18Oware used, indicating that offshore-onshore variability in surface proxy δ18O is primarily influenced by seawater freshening. Simulated bottom water temperatures in the NAMS are also reproduced from biogenic calcite δ18O using model-based values of epicontinental δ18Ow, suggesting that benthic marine fossil δ18O is also influenced by seawater freshening and coastal upwelling. In addition, glacial-interglacial variations in nearshore seawater freshening counteract the effects of temperature on marine biogenic δ18O values, suggesting that salinity effects should be considered in δ18O-based estimates of glacioeustatic sea level change from nearshore regions of the NAMS. Our results emphasize the importance of constraining epicontinental dynamics for interpretations of marine biogenic δ18O as proxies of paleotemperature, salinity, and glacioeustasy.
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Constraining Uncertainties in Marine Calcifier Oxygen Isotope Values (δ18O ${\boldsymbol{\delta }}^{\mathbf{18}}\mathbf{O}$) Across Latitudes and Kingdoms Using a Proxy System Modeling Framework
Abstract Paleoceanographic proxy archives encode information about the marine environment, which can yield key insights into past climate variability. In particular, marine calcifiers' stable oxygen isotopic composition () tells us about seawater temperature and oxygen isotope composition. Here, we use a proxy system model (PSM) framework to systematically evaluate the drivers of skeletal/shell in three taxa of fast‐growing marine calcifiers (crustose coralline algae, bivalves, and sclerosponges) from disparate locations, including high latitudes and deeper waters. We evaluate the impact of the quality of environmental data, the recording season in which the calcifier might document the environmental variability, and the importance of uncertainties on the PSM. Whereas the overall PSM‐modeled captured the measured well at some locations, local environmental variability derived from a reanalysis product and chronological uncertainties limit the ability to effectively model at other locations. Using the PSM approach we highlight the complexity of interpreting as seawater temperature and oxygen isotope composition in these remote locations.
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- PAR ID:
- 10565712
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 39
- Issue:
- 12
- ISSN:
- 2572-4517
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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