Ocean Acidification

About one third of carbon dioxide (CO2) released by human activities since the start of the Industrial Revolution in the 1800s has been taken up by the oceans. This addition of anthropogenic CO2 has altered the basic ocean chemistry, specifically the marine carbonate system. Carbon dioxide dissolves in the surface water and forms carbonic acid which has decreased ocean pH by 0.1 units over the past 200 years. If CO2 emissions increase as projected by the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios, by 2100, the global surface ocean pH will reduce further by 0.3 to 0.5 units.

The most direct biological impact of lowed pH will be on organisms that form calcium carbonate (CaCO3) shells and skeletons, because a decline in pH decreases the saturation state of CaCO3.. The surrounding seawater needs to be saturated with carbonate ions to allow shells to form and to protect shells from dissolution (or breakdown into individual ions).

DFO scientists are studying ocean acidification on all three of Canada's coasts:

  • Atlantic: pH in the bottom waters of the Lower St. Lawrence Estuary has decreased notably by 0.2 to 0.3 pH units over the past 70 years in response to increases in atmospheric CO2. As a result of this exposure to corrosive waters, bottom-dwelling, carbonate-secreting organisms, such as mollusks, bivalves, and benthic foraminifera, must now expend more energy to secrete their skeletons and aragonite shells (a crystal form of calcium carbonate). Further, the Arctic outflow through the Canadian Arctic Archipelago (CAA) influences the highly productive Canadian Atlantic ecosystem. The Arctic outflow is more “corrosive” than other waters in the region and preconditions of Canada's east coast might make it more susceptible to future variations.
  • Pacific: The sub-surface water of the Pacific inherently contains high CO2 concentration due to the age of water. This low pH water is brought to the surface over the British Columbia continental shelf during summer by seasonal upwelling. While this upwelling is a natural phenomenon, the oceanic uptake of anthropogenic CO2 has increased the acidity so that for brief periods surface waters are already undersaturated with respect to aragonite (pH < 7.7) on parts of the coast. The combination of higher carbon concentrations with projected increases in upwelling winds along the west coast will act to exacerbate this problem over the next few decades. Historical data of pteropods, an important food source for salmon, are being examined in the context of model predictions.
  • Arctic: DFO scientists are currently involved in various regional and international studies to more accurately describe the frequency and extent of acidification events, to identify areas that are the most vulnerable to acidification and to better understand the potential impacts on marine organisms. Current research indicates that the uptake of CO2 from the atmosphere is accelerated in the Arctic due to the cold water temperatures. This, combined with more rapid sea ice melt, is making the Arctic particularly vulnerable to ocean acidification.

At an international level, DFO is involved in the Arctic Monitoring Assessment Programme (AMAP). AMAP leads many circumpolar environmental monitoring activities of the Arctic Council.

Information about the DFO scientists working on ocean acidification science activities can be found here.

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