Spring 2008 Seminar Series

Dr. Andreas J. Andersson

Abstract

Acidification of seawater owing to burning of fossil fuels has raised serious concerns as to its consequences for marine organisms and ecosystems, especially those organisms producing shells, tests or skeletons of calcium carbonate. Results from numerical modeling simulations using the Shallow-water Ocean Carbonate Model (SOCM), demonstrate that biogenic calcification and production of CaCO3 in the global coastal ocean and in carbonate ecosystems in general will significantly decrease in the future as a result of ocean acidification. Dissolution of metastable carbonate minerals will significantly increase and will eventually exceed net production of CaCO3. However, CaCO3 dissolution will not produce sufficient alkalinity to buffer significantly the surface ocean pH changes on timescales of decades to centuries. Results from mesocosm experiments and natural environments exhibiting elevated CO2 conditions confirm the numerical modeling results of SOCM. In addition to increased CaCO3 dissolution, and reduced growth of corals and calcifying algae, mesocosm results show that the recruitment success of crustose coralline algae (CCA) and vermitids are significantly impaired by elevated seawater CO2 conditions. Furthermore, observations from Devil's Hole, Bermuda, demonstrate that metastable carbonate minerals such as Mg-calcite are the first responders to ocean acidification and subject to selective dissolution according to mineral stability. The observed maximum rate of dissolution in this environment is close to current estimates of the average production of CaCO3 on coral reefs, confirming that coral reefs and other carbonate ecosystems may become subject to a net loss in carbonate material in the future as a result of anthropogenic ocean acidification.