It is well-established knowledge that the oceans are important sinks for human-made carbon dioxide (CO2) emissions. Each year the oceans absorb about twenty five percent of the CO2 emissions caused by the burning of fossil fuels. Increasing CO2 emissions change the ocean chemistry towards less alkaline conditions: The ocean pH decreases – a process also termed ocean acidification. If the ocean pH gets lower, marine organisms, which produce calcium carbonate shells are expected to have more difficulties to produce these shells (e.g. corals and small snails which are an important part of the plankton food chain). Ocean acidification is an ongoing process and is expected to become a more severe problem in the future due to rising CO2 emissions.
An international research team, including Christoph Heinze from the Bjerknes Centre, carried out a realistic biogeochemical ocean circulation computer simulation with global coverage trying to determine how early the large-scale effect of ocean acidification on decreasing calcium carbonate shell material production could be observed by standard tracer measurements. Due to the limited knowledge on how ocean acidification affects marine calcium carbonate shell production, which also varies from species to species, the scientists can only present a range of possible scenarios for changes in calcium carbonate shell material production and rising atmospheric CO2.
Changes of calcium carbonate production are reflected in an oceanic tracer called ‘alkalinity’. Alkalinity can easily be measured. The model computations show that changes in ocean alkalinity, due to calcium carbonate production changes, may be clearly detectable around year 2040. The strongest signal will become visible in the tropical ocean where absolute rates of calcium carbonate production are highest and therefore, also potential production decreases will be largest. As the present data series for ocean alkalinity is not long enough, a potentially ongoing strong decrease in ocean calcium carbonate production cannot be ruled out. However, such a decrease is considered unlikely in view of present evidence from process studies. In any case, long time series of ocean carbon measurements including alkalinity must be continued in order to help detecting acidification-induced changes in ocean ecosystems. Furthermore, alternative detection methods for the large-scale effects of ocean acidification have to be developed in order to prepare for a world with a high CO2 and low pH ocean.
Reference:
Ilyina, T.(1), R. E. Zeebe, E. (1) Maier-Reimer (2), and C. Heinze (3) (2009), Early detection of ocean acidification effects on marine calcification, Global Biogeochem. Cycles, 23, GB1008, doi:10.1029/2008GB003278.
1 Department of Oceanography, School of Ocean and Earth Science and
Technology, University of Hawaii, Honolulu, Hawaii, USA.
2 Max Planck Institute for Meteorology, Hamburg, Germany.
3 Geophysical Institute and Bjerknes Centre for Climate Research,
University of Bergen, Bergen, Norway