Every once in awhile I like to catch up on how our ongoing destruction of life in the oceans is progressing. If some recent results are anything to go by, things are humming right along. I haven't looked at acidification of the oceans since August, 2010, when I posted The "Other" Carbon Problem — Ocean Acidification, so it's time to take up this happy subject once again. The news comes out of the University of Hawaii, where researchers have found unprecedented, man-made trends in oceans acidity.
Nearly one-third of CO2 emissions due to human activities enters the world’s oceans. By reacting with seawater, CO2 increases the water’s acidity, which may significantly reduce the calcification rate of such marine organisms as corals and mollusks, resulting in the potential loss of ecosystems. The extent to which human activities have raised the surface level of acidity, however, has been difficult to detect on regional scales because it varies naturally from one season and one year to the next, and between regions, and direct observations go back only 30 years.
The study was published in the January 22, 2012 online issue of Nature Climate Change.
The team of climate modelers, marine conservationists, ocean chemists, biologists and ecologists, led by Tobias Friedrich and Axel Timmermann at the International Pacific Research Center at the University of Hawai‘i at Mānoa, came to their conclusions by using Earth system models that simulate climate and ocean conditions 21,000 years back in time, to the Last Glacial Maximum, and forward in time to the end of the 21st century.
In their models, they studied changes in the saturation level of aragonite (a form of calcium carbonate) typically used to measure ocean acidification. As acidity of seawater rises, the saturation level of aragonite drops. Their models captured the current observed seasonal and annual variations in this quantity in several key coral reef regions.
Today’s levels of aragonite saturation in these locations have already dropped five times below the pre-industrial range of natural variability. For example, if the yearly cycle in aragonite saturation varied between 4.7 and 4.8, it varies now between 4.2 and 4.3, which – based on another recent study – may translate into a decrease in overall calcification rates of corals and other aragonite shell-forming organisms by 15%. Given the continued human use of fossil fuels, the saturation levels will drop further, potentially reducing calcification rates of some marine organisms by more than 40% of their pre-industrial values within the next 90 years.
Living organisms need time to adjust to acidification of the oceans. Unfortunately, the man-made rate of change in ocean acidity is happening far too swiftly to allow those adjustments to occur.
“In some regions, the man-made rate of change in ocean acidity since the Industrial Revolution is a hundred times greater than the natural rate of change between the Last Glacial Maximum and pre-industrial times,” emphasized Friedrich. “When Earth started to warm 17,000 years ago, terminating the last glacial period, atmospheric CO2 levels rose from 190 parts per million (ppm) to 280 ppm over 6,000 years. Marine ecosystems had ample time to adjust. Now, for a similar rise in CO2 concentration to the present level of 392 ppm, the adjustment time is reduced to only 100 – 200 years.”
As I was reading this press release, it seemed important to note that the "models" these researchers used are only as reliable as the assumptions that go into them.
On a global scale, coral reefs are currently found in places where open-ocean aragonite saturation reaches levels of 3.5 or higher. Such conditions exist today in about 50% of the ocean – mostly in the tropics. By end of the 21st century this fraction is projected to be less than 5%. The Hawaiian Islands, which sit just on the northern edge of the tropics, will be one of the first to feel the impact...
“Our results suggest that severe reductions are likely to occur in coral reef diversity, structural complexity and resilience by the middle of this century,” said co-author Timmermann.
Regarding CO2 emissions and their absorption into the oceans, these Hawaii researchers have extrapolated "business-as-usual" (BAU) for the rest of the 21st century. If you don't believe BAU can continue for another 90 years, or even another 40 years, you need to take such dire predictions with a grain of salt. That said, whatever the outcome, I don't doubt that rapid acidification will do great damage to all life in the sea which uses calcium carbonate to build skeletons and hard shells.
I think of acidification as the coup de grâce for marine life in so far as it comes on top of rampant over-fishing and seafloor bottom-trawling. Thus I was puzzled to read this result from the recent Nereus Predicting The Future Oceans conference held at the University Of British Columbia.
Adding ocean acidification and deoxygenation into the mix of climate change predictions may turn “winner” regions of fisheries and biodiversity into “losers,” according to research released today by University of British Columbia researchers.
Previous projections have suggested the effects of warmer water temperature would result in fish moving pole-ward and deeper towards cooler waters – and an increase of fish catch potential of as much as 30 per cent in the North Atlantic by 2050.
Warmer oceans would herd the fish into deeper, cooler waters, which would make them easier to catch. The projected increase in the North Atlantic was 30% by 2050. I wondered what they meant by this. This sounded a little "fishy" to me. Did they mean a projected increase from 17 wild-caught fish to 23 fish?
Accounting for effects of de-oxygenation and ocean acidification, however, some regions may see a 20-35 per cent reduction in maximum catch potential by 2050 (relative to 2005) – depending on the individual species’ sensitivity to ocean acidification.
Oh, I see. Instead of there being 17 wild fish to catch in the North Atlantic in 2050, there will be only 11 fish.
That's bad news!
Bonus Video — A Sea Change (trailer)