Nature Reports Climate Change, 18 December 2008 | doi:10.1038/climate.2008.140
by Alicia Newton
Science 322, 1671–1674 (2008)
Scientists have uncovered evidence that the oceanic calcium concentrations have fluctuated widely over the past 28 million years. The concentration of marine calcium has important implications for ocean alkalinity and for the absorption and storage of atmospheric carbon dioxide in the deep sea.
Previous efforts to understand the calcium cycle based on ratios of different isotopes, or forms, of calcium in marine carbonates, have been hampered by changes in environmental conditions in the ocean that also affect the ratios. To avoid this artefact, Elizabeth Griffith of Stanford University, California, and colleagues turned to tiny crystals of barite, a sulphur-based mineral formed in sea water. They measured the ratio of calcium isotopes trapped in the crystals, which is believed to be unaffected by environmental variability. The group found that the amount of dissolved calcium in the oceans — as well as the isotopic composition of that calcium — has varied dramatically during the past 28 million years.
The most pronounced change occurred 13 million years ago, as the climate cooled and Antarctic ice sheets began to increase. The discovery that marine calcium concentrations have been unstable over long geological periods represents a considerable advance in the understanding of global biochemical cycles, which form a crucial component of the climate system.
Link to article: http://www.nature.com/climate/2009/0901/full/climate.2008.140.html