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New Global Maps Detail Ocean Acidification

11.11.2014
11.11.2014 11:38 Age: 2 yrs

Ocean acidity is changing in step with rising CO2 emissions, according to a study by Columbia University

Click to enlarge. In northern winter, the Bering Sea, dividing Alaska and Siberia, becomes the most acidic region on earth (in purple) as shown in this February 2005 acidity map in pH scale. Temperate oceans are less acidic. The equatorial Pacific is left blank due to its high variability around El Niño and La Niña events. Courtesy: Taro Takahashi

Click to enlarge. The saturation state of the mineral aragonite, essential to shell-builders, tends to fall as waters become more acidic. The South Pacific Ocean is heavily oversaturated with respect to aragonite (in red) while the polar oceans (in blue) are less saturated, as shown in this February 2005 map. The pink lines represent approximate polar sea ice edges. Courtesy: Taro Takahashi

Click to enlarge. Taro Takahashi has spent more than four decades measuring the changing chemistry of the world’s oceans. Here, aboard the R/V Melville, he celebrates after sampling waters near the bottom of the Japan Trench in 1973. Courtesy: Lamont-Doherty archives.

 

From Columbia University2) humans have put in the atmosphere over the last two hundred years. But their help in offsetting global warming has come at a price: the oceans are growing more acidic as they absorb our excess CO2. To what extent ocean acidification may harm marine life and ecosystems is still unclear, but already signs of stress have appeared in corals, mollusks and other shell-builders living in regions with naturally more acidic water. Since the industrial era began, average surface seawater pH in temperate oceans has fallen from 8.2 to 8.1 by 0.1 pH unit, equal to a 30 percent increase in acid concentration. (A lower pH indicates more acidic conditions.)

Least variation

2-rich water from the deep ocean causes surface waters to become more acidic. Acidification of the Arctic Ocean in winter causes aragonite levels to fall, slowing the growth of pteropods, planktic snails that feed many predator fish.

The maps reveal that the northern Indian Ocean is at least 10 percent more acidic than the Atlantic and Pacific oceans, which could be due to its unique geography. Cut off from the Arctic Ocean, the chemistry of the northern Indian Ocean is influenced by rivers draining the massive Eurasian continent as well as seasonal monsoon rains.

Long-term data

By analyzing long-term data collected off Iceland, Bermuda, the Canary Islands, Hawaii and the Drake Passage, off the southern tip of South America, Takahashi finds that waters as far north as Iceland and as far south as Antarctica are acidifying at the rate of 5 percent per decade. His estimate corresponds to the amount of CO22

Seasonal upwelling

Ocean acidification is already having an impact, especially in places where the seasonal upwelling of deep water has made seawater naturally more acidic. In a  recent study by researchers at NOAA, more than half of the pteropods sampled off the coast of Washington, Oregon and California showed badly dissolved shells. Ocean acidification has been linked to fish losing their ability to sniff out predators, and the die-off of baby oysters in hatcheries off Washington and Oregon, where more acidic deep water comes to the surface each spring and summer.  

By 2100, ocean acidification could cost the global economy $3 trillion a year in lost revenue from fishing, tourism and intangible ecosystem services, according to arecent United Nations report.  The U.S. Government Accountability Office, the watchdog arm of Congress, has reached similar findings and recommended that President Obama create a research and monitoring program dedicated to ocean acidification.

Other authors of the study: Stuart Sutherland, David Chipman (now retired), John Goddard and Cheng Ho, all of Lamont-Doherty; and Timothy Newberger, Colm Sweeney and David Munro, all of University of Colorado, Boulder.

Highlights

Marine Chemistry reports the highlights of this research as:

Based on observations, pH and CaCO3 saturation in global surface ocean is computed.

pH in the global ocean surface waters ranges from 7.9 to 8.2 in the year 2005.

Warm subtropical oceans have seasonally varying pH ranging from 8.05 to 8.15.

Time-series data show that pH has declined at a mean rate of about -0.002 pH per year.

Warm waters are supersaturated by aragonite by 4.2, whereas cold waters only by 1.2.

Abstract

Climatological mean monthly distributions of pH in the total H+ scale, total CO2 concentration (TCO2), and the degree of CaCO3 saturation for the global surface ocean waters (excluding coastal areas) are calculated using a data set for pCO2, alkalinity and nutrient concentrations in surface waters (depths < 50 m), which is built upon the GLODAP, CARINA and LDEO databases. The mutual consistency among these measured parameters is demonstrated using the inorganic carbon chemistry model with the dissociation constants for carbonic acid by Lueker et al. (2000) and for boric acid by Dickson (1990). Linear potential alkalinity-salinity relationships are established for 24 regions of the global ocean. The mean monthly distributions of pH and carbon chemistry parameters for the reference year 2005 are computed using the climatological mean monthly pCO22 concentrations. In the western Arctic Ocean, aragonite undersaturation is observed. The time-series data from the Bermuda (BATS), Hawaii (HOT), Canary (ESTOC) and the Drake Passage show that pH has been declining at a mean rate of about -0.02 pH per decade, and that pCO2 has been increasing at about 19 μatm per decade tracking the atmospheric pCO2 increase rate. This suggests that the ocean acidification is caused primarily by the uptake of atmospheric CO2. The relative importance of the four environmental drivers (temperature, salinity, alkalinity and total CO2 concentration) controlling the seasonal variability of carbonate chemistry at these sites is quantitatively assessed. The ocean carbon chemistry is governed sensitively by the TA/TCO2 ratio, and the rate of change in TA is equally important for the future ocean environment as is the TCO2 in ocean waters increases in the future.

Citation

Climatological distributions of pH, pCO2, total CO2, alkalinity, and CaCO3

Read the abstract and get the paper here.

Source

News release from Columbia university here.