The United States Department of Energy (DOE)’s Ocean Margins Program (OMP) cruise EN279 in March 1996 provides an important baseline for assessing long-term changes in the carbon cycle and biogeochemistry in the Mid-Atlantic Bight (MAB) as climate and anthropogenic changes have been substantial in this region over the past two decades. The distributions of O 2 , nutrients, and marine inorganic carbon system parameters are influenced by coastal currents, temperature gradients, and biological production and respiration. On the cross-shelf direction, pH decreases seaward, but carbonate saturation state (Ω Arag ) does not exhibit a clear trend. In contrast, Ω Arag increases from north to south, while pH has no clear spatial patterns in the along-shelf direction. In order to distinguish between the effects of physical mixing of various water masses and those of biological activities on the marine inorganic carbon system, we use the potential temperature-salinity diagram to identify water masses, and differences between observations and theoretical mixing concentrations to measure the non-conservative (primarily biological) effects. Our analysis clearly shows the degree to which ocean margin pH and Ω Arag are regulated by biological activities in addition to water mass mixing, gas exchange, and temperature. The correlations among anomalies in dissolved inorganic carbon, phosphate, nitrate, and apparent oxygen utilization agree with known biological stoichiometry. Biological uptake is substantial in nearshore waters and in shelf-slope mixing areas. This work provides valuable baseline information to assess the more recent changes in the marine inorganic carbon system and the status of coastal ocean acidification.
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Tracking the Paleocene‐Eocene Thermal Maximum in the North Atlantic: A Shelf‐to‐Basin Analysis With a Regional Ocean Model
The Paleocene‐Eocene Thermal Maximum (PETM), a transient greenhouse climate interval spurred by a large release of carbon to the ocean‐atmosphere approximately 56 million years ago, provides a geological point of comparison for potential effects of anthropogenic carbon emission. Geochemical proxies and fossil assemblages offer insight into the continental shelf response to the PETM, but global ocean‐atmosphere models cannot resolve shelf processes at sufficient resolution for model‐data comparisons. We present high‐resolution simulations of the pre‐PETM and PETM North Atlantic basin using the Regional Ocean Modeling System (ROMS), including a resolved continental shelf along the eastern margin of North America in the Salisbury Embayment. ROMS' high‐resolution, terrain‐following coordinate system permits greater vertical resolution and eddy resolution along continental margins while also capturing open‐ocean processes. We find that during the PETM, benthic oxygen concentration ([O2]) in the Salisbury Embayment decreases 18% to an average state of year‐round mild hypoxia, while average benthic calcite saturation (Ω) declines from 4.4 to 2.3. These benthic decreases are driven largely by enhanced benthic oxic respiration, which occurs despite no increase in shelf productivity. Instead, increased respiration stems from less vigorous off‐shelf transport of organic matter due to (a) weakened along‐shelf water currents and (b) weakened coastal upwelling that forces productivity closer to the shelf seafloor. Model results do not include riverine inputs, which would have further lowered benthic [O2] and Ω. Our data suggest lowered benthic calcite saturation and mild hypoxia as an upper bound on the oxygenation state of the Salisbury Embayment seafloor during the PETM.
more » « less- NSF-PAR ID:
- 10462454
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 33
- Issue:
- 12
- ISSN:
- 2572-4517
- Page Range / eLocation ID:
- p. 1324-1338
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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