Department of Environmental Earth System Science Seminar:
Ecosystem-Scale Effects of Aragonite Saturation, Temperature, and Nutrients on Coral-Reef Calcification
Jack Silverman
Carnegie Institution, Department of Global Ecology
When: 12:15pm, Wednesday, November 19th
Where: Yang and Yamazaki Energy and Environmental Building, Room 111
Refreshments served at noon
We investigated the relations between net calcification of an entire coral reef in the northern Red Sea and annual changes in aragonite saturation, temperature, and nutrient loading over a two year period, and augmented this study with similar observations in the Great Barrier Reef, Australia. In the Red Sea, average calcification rates varied between 60 ± 20 and 30 ± 20 mmol·m-2·day-1 in the summer and winter, respectively. These changes primarily reflected seasonal differences in aragonite saturation and temperature. Data for the Great Barrier Reef are still being processed.
Calcification rates at the ecosystem scale correlated remarkably well with the kinetics observed in inorganic aragonite precipitation experiments. This is a remarkable finding considering that calcification in coral reefs is primarily a biogenic process; this finding is yet to be explained mechanistically. These relationships are also in agreement with most laboratory studies on individual stony corals and coral mesocosms. The consistency of these responses at levels ranging from inorganic kinetics through the ecosystem scale suggests that these relationships are sufficiently robust to make predictions of coral reef response to ocean acidification and global warming.
Finally, in a number of nighttime measurements, we observed net aragonite dissolution despite the supersaturated state of overlying reef water. This apparent dissolution is most likely biologically mediated. Aragonite dissolution, combined with decreasing aragonite precipitation, suggests that at least some reefs will be undergoing net dissolution by the time atmospheric carbon dioxide concentration doubles over its pre-industrial value.