Co2 and the Oceans: Carbon Balance, Temperature, and Acidification
On various time scales, atmospheric CO2 and CH4, global temperature, marine carbon chemistry and pH, and sea level change in a nearly synchronous manner, although there are time lags among the variables. In this presentation, we explore, mainly from modeling and observational results, the trends in these variables and the processes controlling them. During the long-term Hot Houses (Greenhouses) of the Phanerozoic, atmospheric CO2 and CH4 were relatively high, seawater Mg and Ca concentrations were low and high, respectively, relative to modern seawater; carbonate mineral saturation was elevated despite depressed pH (the calcite-dolomite seas); the planet was warm; and sea level high. The opposite was true for the Ice Houses of the Phanerozoic (the aragonite seas). The fundamental driver of these different states of the Earth system was plate tectonics and accompanying feedbacks in the system. During the Pleistocene Ice Age, relatively high atmospheric CO2 and CH4 levels, slightly basic and lower dissolved inorganic carbon oceans, warm temperatures, and high sea levels characterized interglacial stages. The contrary was true for the glacial stages. The different states of the Ice Age were mainly a result of initial changes in Milankovitch forcing abetted by feedbacks, including weathering, in the Earth system. In contrast to these natural changes in the carbon cycle, in the Anthropocene, atmospheric CO2 and CH4 levels have risen mainly because of human activities, such as the burning of fossil fuels and land use changes. In the late pre-industrial era, the global ocean was a source of CO2 to the atmosphere because of net heterotrophy and production of carbonates but, except for the global coastal ocean, it is now a sink. As a result of rising atmospheric greenhouse gas concentrations and the enhanced greenhouse effect, the global mean surface temperature has increased almost 1 oC since the 19th century. Much of the warming of the last four decades from this enhanced greenhouse effect has been soaked up by the ocean to be stored for years to decades before release. The ocean has also absorbed about one third of the total anthropogenic CO2 emissions from human activities. A result of the uptake of anthropogenic CO2 by the ocean has been its acidification. If current trends continue, future temperature changes and ocean acidification could have severe consequences for marine calcifying organisms and perhaps also other organism communities.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009