Things just went from worse to worser in the Southern Ocean: According to a new study published in the Proceedings of the National Academy of Science, seasonal changes in pH and the concentration of carbonate could be compounding the impact of anthropogenic emissions, speeding up the process of ocean acidification by almost 30 years, reports ABC Science’s Bianca Nogrady. Pushing the ocean much further could weaken the Southern Ocean’s ability to absorb large amounts of carbon dioxide and dramatically alter its ecosystem structure, the lead author, Ben McNeil of the University of South Wales, warns.
The end of marine life as we know it?
The consequences for marine organisms, particularly those which form shells or skeletons made out of calcium carbonate, would be devastating. A low pH reduces the availability of carbonate and bicarbonate ions in the ocean; if carbonate levels are low enough, calcium carbonate (CaCO3) becomes more soluble and dissolves back into the water, inhibiting the ability of shelled plankton like coccolithophores or pteropods to make their shells.
As surface waters become more acidic, the “saturation horizon,” which is defined as the natural boundary in the water column below which CaCO3 dissolves, is expected to rise — reducing precious habitat space for these and other organisms. This matters because many other organisms up the food chain depend either directly (zooplankton) or indirectly (fish and other larger predators) on their presence. (In other words, many of these species are likely to go extinct.)
Picturing a worst worst-case scenario
Previous studies had predicted that the Southern Ocean’s surface waters would become undersaturated with respect to aragonite, one of two forms of CaCO3 (the more soluble one), by mid-century (550 parts per million by 2060, according to Julia Whitty). Several recent models have determined that surface carbonate ion concentrations have already fallen by almost 10 percent since pre-industrial times; they are likely to fall much further by century’s end if present trends continue. (John recently noted that ocean acidity levels were up a whopping 30 percent since the advent of the Industrial Revolution.)
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Jeremy Elton Jacquot, treehugger, 11 December 2008. Full article.
