MEPS 373:265-273 (2008)  -  DOI:

Contribution to the Theme Section ‘Effects of ocean acidification on marine ecosystems’


Life on the margin: implications of ocean acidification on Mg-calcite, high latitude and cold-water marine calcifiers

Andreas J. Andersson1,*, Fred T. Mackenzie2, Nicholas R. Bates1

1Bermuda Institute of Ocean Sciences, 17 Biological Station Lane, Ferry Reach, St. George’s GE01, Bermuda
2Department of Oceanography, School of Ocean and Earth Science and Technology, University of Hawaii,
1000 Pope Road, Honolulu, Hawaii 96822, USA

ABSTRACT: Future anthropogenic emissions of CO2 and the resulting ocean acidification may have severe consequences for marine calcifying organisms and ecosystems. Marine calcifiers depositing calcitic hard parts that contain significant concentrations of magnesium, i.e. Mg-calcite, and calcifying organisms living in high latitude and/or cold-water environments are at immediate risk to ocean acidification and decreasing seawater carbonate saturation because they are currently immersed in seawater that is just slightly supersaturated with respect to the carbonate phases they secrete. Under the present rate of CO2 emissions, model calculations show that high latitude ocean waters could reach undersaturation with respect to aragonite in just a few decades. Thus, before this happens these waters will be undersaturated with respect to Mg-calcite minerals of higher solubility than that of aragonite. Similarly, tropical surface seawater could become undersaturated with respect to Mg-calcite minerals containing ≥12 mole percent (mol%) MgCO3 during this century. As a result of these changes in surface seawater chemistry and further penetration of anthropogenic CO2 into the ocean interior, we suggest that (1) the magnesium content of calcitic hard parts will decrease in many ocean environments, (2) the relative proportion of calcifiers depositing stable carbonate minerals, such as calcite and low Mg-calcite, will increase and (3) the average magnesium content of carbonate sediments will decrease. Furthermore, the highest latitude and deepest depth at which cold-water corals and other calcifiers currently exist will move towards lower latitudes and shallower depth, respectively. These changes suggest that anthropogenic emissions of CO2 may be currently pushing the oceans towards an episode characteristic of a ‘calcite sea.’

KEY WORDS: Ocean acidification · Calcification · Carbonate dissolution · Mg-calcite · High latitude · Aragonite · Saturation state · Calcite sea

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Cite this article as: Andersson AJ, Mackenzie FT, Bates NR (2008) Life on the margin: implications of ocean acidification on Mg-calcite, high latitude and cold-water marine calcifiers. Mar Ecol Prog Ser 373:265-273.

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