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Increasing atmospheric CO2 and eutrophication combine to acidify coastal bottom waters

Dissolution of carbon dioxide (CO2) from rising atmospheric CO2 is acidifying ocean water; but a second environmental problem, eutrophication, is having a similar effect in coastal bottom waters. This occurs because anthropogenic inputs of nutrients fuel massive algal blooms, which deplete bottom waters of oxygen (O2) and release CO2 when the organic matter from these blooms is respired by bacteria.

Based on a biogeochemical model, these CO2 inputs are predicted to decrease current pH values by 0.25 to 1.1 units, effects that increase with decreasing temperature and salinity. The model predictions were verified by pH data from hypoxic zones in the northern Gulf of Mexico and Baltic Sea, two well known eutrophic systems. These decreases in pH are well within the range that adversely impacts marine fauna.

Model calculations show that the acidification from respiratory CO2 inputs interacts in a complex fashion with that from increasing atmospheric CO2, and that these pH effects are more than additive at intermediate to higher temperatures. These synergistic interactions have important biological implications in a future world with increasing atmospheric CO2, higher anthropogenic inputs of nutrients, and rising temperatures from CO2-linked global warming.

These findings will be presented in a poster at the Ocean Sciences Meeting in Salt Lake City, February 15-19.

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Shorter web link for sharing: http://coastalscience.noaa.gov/news/?p=4285

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