Southern Ocean Could Hit Ocean Acidification Tipping Point 30 Years Early


Image from huangjiahui

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.)

This passage from an article in Mongabay puts the study in (stark) perspective:

Oceans worldwide absorbed approximately 118 billion metric tons of carbon between 1800 and 1994 according to a report published in 2006 by scientists at the National Center for Atmospheric Research and NOAA, resulting in increased ocean acidity. Should CO2 emissions continue at their current rate, scientists project that global ocean pH levels could drop from 8.1 today to 7.7 by 2100.

In the past, changes in ocean acidity have triggered mass extinction events. According to a study published in the September 2006 issue of Geology, dramatically warmer and more acidic oceans may have contributed to the worst mass extinction on record, the Permian extinction. During the extinction event, which occurred some 250 million years ago, about 95% of ocean's life forms became extinct.


Oceana report: Fixing ocean acidification now would save billions
This study coincides with a new report, entitled "Acid Test," released today by our friends at Oceana, which finds that slowing ocean acidification (stopping it completely is now, unfortunately, not a possibility) could save billions in lost revenue from the fishing and eco-tourism industries down the road. The actions they believe policymakers should take include:

* Adopt a policy of stabilizing atmospheric carbon dioxide at 350 parts per million or below (that would require an 85 percent cut in emissions below 2000 levels by 2050)
* Promote energy efficiency and low carbon fuels
* Transition quickly to alternative energy sources
* Regulate carbon releases
* Preserve natural resilience of marine ecosystems by protecting them from overfishing and pollution

The science in the report is rock-solid: The authors based many of their recommendations on the work of top climate scientists like NASA's James Hansen (hence the 350 ppm figure, which is also the level eco-activists like Bill McKibben say we should cap CO2 at). It doesn't exactly make for uplifting reading, but I hope some of President-elect Obama's science advisers will pick up on it.

Via: The Blue Marble: Southern Ocean Nears Acid Tipping Point
More about ocean acidification
Acidification: 100 Years in the Future
Ocean Acidification Conference: Acidity Up 30% Since Industrial Revolution - Producing Toxic Assets For The World
Volcanic Vents Shed Light on a Future of Ocean Acidification

Tags: Carbon Dioxide

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