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Ocean margins as an increasing sink for the atmospheric carbon dioxide

Wei-Jun Cai, University of Delaware, (Presenter)
Goulven Laruelle, Université Libre de Bruxelles,
Xinping Hu, Texas A&M University – Corpus Christi,
Pierre Regnier, Université Libre de Bruxelles,

The partial pressure of carbon dioxide (pCO2) in the open ocean has increased following that of the atmosphere, a process leading to ocean acidification with negative impacts on marine organisms and ecosystems. Although previous researchers speculated that pCO2 in coastal oceans may not follow this pattern, no evidence has been provided on global scale. Using a recently available global database, we report that the wintertime pCO2 increase in coastal oceans has lagged behind the atmospheric increase in recent decades, resulting in an increase in the air-sea pCO2 gradient and a likely strengthening of the coastal ocean sink for anthropogenic CO2. We postulate that the increase in air-sea pCO2 gradient resulted from a much smaller pCO2 increase in the coastal ocean than in the atmosphere as a consequence of a faster CO2 exchange rate of the coastal oceans with the subsurface deep ocean than with the atmosphere. This fast cross-shelf exchange dilutes the accumulation of anthropogenic CO2 in coastal waters. To illustrate this mechanism, we used a simple box model, which assumes constant physical and biological parameters but allows the atmospheric pCO2 to increase according to RCP6.0 until 2100. Simulations show that surface water pCO2 increase in the coastal ocean is well behind that of the atmospheric pCO2 when the cross-shelf water exchange rate is between 0.25-2.0% per day or the coastal water residence time is between 1.5 and 12 months. Field data and model simulations also suggest that the coastal ocean has switched from a source to a sink of CO2 for the atmosphere, and this sink is increasing with time. Thus, as the open ocean’s capacity for uptake of anthropogenic CO2 may level off or even decrease in coming decades, the coastal ocean will become an increasingly important pathway for global ocean CO2 uptake and subsequent ocean acidification via cross-margin export to the deep open ocean.

Presentation Type:  Poster

Session:  Carbon Monitoring System (CMS) Posters   (Mon 1:30 PM)

Associated Project(s): 

  • Lohrenz, Steve: An Integrated Terrestrial-Coastal Ocean Observation and Modeling Framework for Carbon Management Decision Support ...details
  • Lohrenz, Steve: Assessing Impacts of Climate and Land Use Change on Terrestrial-Ocean Fluxes of Carbon and Nutrients and Their Cycling in Coastal Ecosystems ...details
  • Lohrenz, Steve: Development of Observational Products and Coupled Models of Land-Ocean-Atmospheric Fluxes in the Mississippi River Watershed and Gulf of Mexico in Support of Carbon Monitoring ...details
  • Robbins, Lisa: Air-Sea CO2 Flux and Carbon Budget Synthesis and Modeling in the Entire Gulf of Mexico ...details

Poster Location ID: 133


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