Tracking the Paleocene‐Eocene Thermal Maximum in the North Atlantic: A Shelf‐to‐Basin Analysis With a Regional Ocean Model

Abstract

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.

Environmental and Geomorphological Changes on the Eastern North American Continental Shelf Across the Paleocene‐Eocene Boundary

“…Regional modeling of the Salisbury Embayment supports the deoxygenation of shelf sediments during the PETM onset. In addition to any changes related to increased riverine influence, weakened coastal upwelling and along‐shelf currents resulted in a decrease in benthic oxygen concentration (Hantsoo et al, ). Also following the CIE onset, planktic species richness increased slightly with the addition of A. africana and A. multicamerata .…”

Surface ocean warming and acidification driven by rapid carbon release precedes Paleocene-Eocene Thermal Maximum

“…Mainly through laboratory culture experiments, these secondary controls are recognized as salinity ( 70 ), carbonate chemistry (pH or carbonate ion) ( 71 ), and secular variation in seawater Mg/Ca (Mg/Ca sw ) for deep-time reconstructions ( 72 ). Late Paleocene Mid-Atlantic coastal surface salinity values are estimated to be approximately 35 based on an average for the upper 200 m in the North Atlantic Ocean in the PETM coastal model simulation of Hantsoo et al ( 73 ). Salinity variations over the PETM at nearby New Jersey sites are computed to be less than 3 units ( 6 , 26 ) and therefore contribute an uncertainty of ~1°C on Mg/Ca-derived temperatures.…”

“…To evaluate the uncertainty of Paleogene δ 11 B sw composition on the determination of ocean pH, a similar Monte Carlo approach used by Gutjahr et al ( 11 ) was adopted. Estimation of background Paleocene hydrographic parameters (e.g., temperature and salinity) was based on a Regional Ocean Modeling System (ROMS) simulation of shelf conditions within the Salisbury Embayment ( 73 ). Following the approach of previous PETM boron isotope studies, pre-POE δ 11 B values were normalized to a fixed surface ocean pH value because of the uncertainty associated with δ 11 B sw ( 6 , 11 , 17 , 27 ).…”

“…S8). Based on the ROMS Mid-Atlantic coastal modeling ( 73 ), we assume an average Paleocene shelf bottom water temperature of 22°C, salinity equal to 35, and pH of 7.67. Using this hydrographic information, we set pre-POE δ 11 B values to pH = 7.67, which, when coupled with our measured δ 11 B, required a δ 11 B sw = 37.8 ± 0.46‰.…”

Constructing a model including the cryptic sulfur cycle in Chesapeake Bay requires judicious choices for key processes and parameters

“…An updated version of this code (with a number of improvements) was published by Hantsoo et al. [8] .…”