Greatest threat to marine ecosystem is…

UPDATE: Jo Nova links to a study which contains similar conclusions:

“Here, we present a compilation of continuous, high-resolution time series of upper ocean pH, collected using autonomous sensors, over a variety of ecosystems ranging from polar to tropical, open-ocean to coastal, kelp forest to coral reef. These observations reveal a continuum of month-long pH variability with standard deviations from 0.004 to 0.277 and ranges spanning 0.024 to 1.430 pH units. The nature of the observed variability was also highly site-dependent, with characteristic diel, semi-diurnal, and stochastic patterns of varying amplitudes. These biome-specific pH signatures disclose current levels of exposure to both high and low dissolved CO₂, often demonstrating that resident organisms are already experiencing pH regimes that are not predicted until 2100.“

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“Ocean acidification.” How many times do we see that phrase in the mainstream media? The phrase intentionally creates the impression that the oceans are slowly turning into battery acid, eating away at shellfish and coral just as the phosphoric acid in fizzy drinks dissolves teeth. Just today in the Silly Moaning Herald publishes another alarming piece on the subject:

The uptake of carbon dioxide into the oceans drives a change in ocean chemistry, changing hydrogen levels and the concentration of carbonate ions that pteropods and other organisms use to build their calcium carbonate shells.

The higher acidity also eats away at the organisms’ shells.

“Southern Ocean waters are absorbing more carbon dioxide than anywhere else on the planet so if we are going to see an effect on the biology were going to see it first in the Southern Ocean,” Dr Roberts said.

Acidification is expected to increase significantly over the next century.

“We often call it the evil twin of climate change,” Dr Roberts said.

“The little critters that have got shells that are going to be eaten away by the acid, they’re in trouble.

“We’re really worried about whether they are going to be here in the future and how that will change the Southern Ocean food chain because it’s the biggest ocean in the world. (source)

Firstly, “acidification” is the term used because it sounds scarier than the more accurate alternatives “becoming less alkaline”, or “becoming more neutral” since as discussed here, the pH of the oceans has dropped slightly from 8.2 to about 8.1, still well short of neutral (7), let alone turning acidic.

Matt Ridley injects some sense into the debate in an article in the Wall Street Journal, in which he argues that natural variation in pH exceeds such tiny anthropogenic changes by at least an order of magnitude, that many studies show that shell formation can actually increase in less alkaline conditions, and that in any case overfishing and pollution are far more damaging to the marine ecosystems than “acidification”:

“On both a monthly and annual scale, even the most stable open ocean sites see pH changes many times larger than the annual rate of acidification,” say the authors of the study, adding that because good instruments to measure ocean pH have only recently been deployed, “this variation has been under-appreciated.” Over coral reefs, the pH decline between dusk and dawn is almost half as much as the decrease in average pH expected over the next 100 years. The noise is greater than the signal.

Another recent study, by scientists from the U.K., Hawaii and Massachusetts, concluded that “marine and freshwater assemblages have always experienced variable pH conditions,” and that “in many freshwater lakes, pH changes that are orders of magnitude greater than those projected for the 22nd-century oceans can occur over periods of hours.”

This adds to other hints that the ocean-acidification problem may have been exaggerated. For a start, the ocean is alkaline and in no danger of becoming acid (despite headlines like that from Reuters in 2009: “Climate Change Turning Seas Acid”). If the average pH of the ocean drops to 7.8 from 8.1 by 2100 as predicted, it will still be well above seven, the neutral point where alkalinity becomes acidity.

The central concern is that lower pH will make it harder for corals, clams and other “calcifier” creatures to make calcium carbonate skeletons and shells. Yet this concern also may be overstated. Off Papua New Guinea and the Italian island of Ischia, where natural carbon-dioxide bubbles from volcanic vents make the sea less alkaline, and off the Yucatan, where underwater springs make seawater actually acidic, studies have shown that at least some kinds of calcifiers still thrive—at least as far down as pH 7.8.

In a recent experiment in the Mediterranean, reported in Nature Climate Change, corals and mollusks were transplanted to lower pH sites, where they proved “able to calcify and grow at even faster than normal rates when exposed to the high [carbon-dioxide] levels projected for the next 300 years.” In any case, freshwater mussels thrive in Scottish rivers, where the pH is as low as five.

Laboratory experiments find that more marine creatures thrive than suffer when carbon dioxide lowers the pH level to 7.8. This is because the carbon dioxide dissolves mainly as bicarbonate, which many calcifiers use as raw material for carbonate.

Human beings have indeed placed marine ecosystems under terrible pressure, but the chief culprits are overfishing and pollution. By comparison, a very slow reduction in the alkalinity of the oceans, well within the range of natural variation, is a modest threat, and it certainly does not merit apocalyptic headlines. (source)

“Does not merit apocalyptic headlines.” Take note, SMH.