Ocean Acidity Update: Wild Oysters Now Sterile

By Bruce E. Johansen

Some of the worst problems from rising levels of carbon dioxide in the atmosphere have nothing to do with the higher temperatures we associate with global warming. Most are nearly invisible. Take, for example, the intensifying acidity of the oceans. We are killing the oceans by overloading them with carbon dioxide, and acidity—not temperature—is the problem. 

Ocean pH is now lower than it has been in 20 million years, and continues to decline, according to marine chemist Richard Feely of NOAA’s Marine Environmental Laboratory in Seattle. Models by Feely and colleagues anticipate that ocean pH will decline from 8.2 before the industrial revolution to 7.8 by 2100 C.E., increasing acidity by about 150 percent. Shells of microscopic oceanic animals already have thinned by up to one-third due to rising levels of carbon dioxide. These animals are at the base of the oceanic food chain. 

The coastal waters of Washington State have become so acid that wild oysters have not reproduced since 2005. Rising atmospheric levels of carbon dioxide are combining with industrial discharges, septic runoff and motor-vehicle traffic to accelerate the acidity of waters off the Washington State coast and in Puget Sound. Acidity problems are worst in Hood Canal, site of most of the area's shellfish industry. Scientists from the University of Washington and NOAA warned July 12, 2010 that Western Washington waters had become a hotspot for marine acidity. 

Acidic water kills oyster larvae. On the oceanic coast, the highest acidity is being found near the coast, the area richest in marine life, Coastal acidity is being carried by ocean currents into the enclosed waters of Hood Canal and Puget Sound, raising levels from industrial sources there. Hood Canal is becoming a dead zone as pollution and runoff from septic tanks kills fish, octopus, crab, and other sea life. pH in southern Puget Sound was as low as 7.4 by 2010. 

Effects of increasing acidity of the world’s oceans will continue for “tens of thousands of years,” according to an analysis by Richard A. Kerr in Science June 18, 2010. Nothing in geologic records describes effects as sudden and severe as the present plunge in pH, so future effects on marine wildlife are unknown. Researchers are seeing signs that coral growth does slow, oyster larvae suffer, and plankton with calcareous skeletons lose mass,” according to this study. 

The Paleocene-Eocene Thermal Maximum 55.8 million years ago presents something of an analogue to the changes taking place in the atmosphere and oceans today with respect to pH change and rise in CO2 level. Today, however, the change is occurring at least ten times as quickly, according to paleoceanographer James Zachos of the University of California—Santa Cruz. Nature took several thousand years to vent 2,000 to 7,000 gigatons of carbon dioxide and methane (which oxidized to carbon dioxide) from volcanoes, methane hydrates, peat, or all of these. Human emissions of greenhouse gases are doing the same thing in a few centuries. 

With funding from the Australian Government Department of Climate Change, Will Howard of the Antarctic Climate & Ecosystems Cooperative Research Centre in Australia. and colleagues collected microscopic marine animals called planktonic foraminifera (or forams) from the South Tasman Rise region of the Southern Ocean. They compared the weights of the shells of these modern forams to those trapped in ocean sediments before the industrial revolution and its infusion of carbon dioxide, finding that today’s shell weights are 30 to 35 per cent less than older fossils. This is nearly equal to the amount by which the proportion of carbon dioxidxe has risen in the atmospghere. The findings were described in the March 8, 2009 issue of the journal Nature Geoscience.             

In addition to increasing use of nitrogen-based fertilizers and sewage runoff, accelerating emissions of carbon dioxide into the atmosphere (and its absorption by the oceans) is causing “dead zones”—desolate regions where pollution-fed algae deprive other marine life of oxygen—to expand rapidly. The number of such areas worldwide increased to about 200 by 2008, a 34 per cent rise in two years. 

Given carbon dioxide’s long life in the atmosphere, this trend that could persist for centuries or longer even after greenhouse-gas emissions end. A 100,000-year computer simulation indicates that severe ocean oxygen depletion could last for thousands of years. Dead zones that cover about 2 per cent of ocean surface today could expand to 20 per cent by that time. Our increasing emissions of carbon dioxide are raping the oceans.


Bruce E. Johansen is Jacob J.  Isaacson Professor at the University of Nebraska at Omaha and author of The Encyclopedia of Global Warming Science and Technology (2009). 


Kerr. Richard A. Kerr “Ocean Acidification Unprecedented, Unsettling.” Science 328 (June 18, 2010): 1500-1501. 

Welch, Craig. "Puget Sound Waters Becoming More Corrosive" Seattle Times,  July 13, 2010, B-1, B-2. 


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