Ocean Acidification: The Other CO2 Problem

Step 1: The Oceans absorb atmospheric CO2 produced from fossil fuel combustion

Below is a cross section of three ocean basins, Atlantic, Pacific, and Indian, illustrating the penetration of fossil fuel CO2 into the ocean water. Dark red shows the highest concentration of CO2 derived from fossil fuels; the concentration declines from red to light blue. Dark blue regions of the ocean are not yet affected by fossil fuels. (black peaks represent seamounts on the ocean floor)

Vertical distributions of anthropogenic CO2 concentrations in _mol kg-1 and the supersaturation/ undersaturation horizons for aragonite and calcite along north-south transects in the (A) Atlantic, (B) Pacific, and (C) Indian Oceans.

From Feely, R. A., C. L. Sabine, K. Lee, W. Berelson, J. Kleypas, V. J. Fabry, and F. J. Millero. 2004. Impact of anthropogenic CO2 on the CaCO3 system in the oceans. Science 305:362-366. Reprinted with permission from AAAS.

Step 2: Rising CO2-declining pH

Rising atmospheric CO2 concentrations from the burning of fossil fuels (red diamonds) causes rising CO2 concentrations in seawater (dark blue diamonds) and subsequent decline in ocean pH (light blue diamonds). These blue curves are the ocean-analogs to the famous red 'Keeling Curve' of rising atmospheric CO2 concentrations. They are from field measurements at Mauna Loa station in Hawaii.

Time series of: (a) atmospheric CO2 at Mauna Loa (in parts per million volume, ppmv) (red), surface ocean pH (cyan), and pCO2 (tan) at Ocean Station ALOHA in the subtropical North Pacific Ocean.

From: Doney, S. C., V. J. Fabry, R. A. Feely, and J. Kleypas. 2009. Ocean Acidification: The Other CO2 Problem. Annual Review of Marine Sciences 1 :169-192. Reprinted, with permission, from the Annual Review of Marine Science, Volume 1 © 2009 by Annual Reviews www.annualreviews.org

Step 3: Declining carbonate

Declining carbonate concentrations (both aragonite and calcite) in waters off of Mauna Loa as a result of declining pH (see above). All measurements (atmospheric CO2, ocean pCO2, ocean pH and carbonate) were taken at same site.

Adapted from: Doney, S. C., V. J. Fabry, R. A. Feely, and J. Kleypas. 2009. Ocean Acidification: The Other CO2 Problem. Annual Review of Marine Sciences 1 :169-192. Reprinted, with permission, from the Annual Review of Marine Science, Volume 1 © 2009 by Annual Reviews www.annualreviews.org

Step 4: Reduced calcification in shelled organisms

Corals

Complete loss of carbonate structure in a coral grown at high CO2 concentrations (compare same species in photo A vs. B).

Photographs of O. patagonica. Scale bars indicate 2 mm. (A) Control colony. (B) Sea anemone - like coral polyps following skeleton dissolution in low-pH conditions. (C) Solitary polyps reforming a colony and calcifying after being transferred back to normal seawater following 12 months as softbodied polyps in low-pH conditions. (D) Time series illustrating percent change (average ± SE) in protein per polyp (biomass) and total buoyant weight over 12 months in experimental (pH = 7.4) and control (pH = 8.2) seawater (N = 20). A two-way analysis of variance (time × pH) revealed significant changes (P < 0.001) between treatments over time.

From Fine, M. and D. Tchernov. 2007. Scleractinian coral species survive and recover from decalcification. Science 315 :1811-1811. Reprinted with permission from AAAS.

Coccolithophores

Scanning electron microscopy (SEM) photographs of coccolithophorids under different CO2 concentrations. Emiliania huxleyi corresponding to pCO2 levels of about 300 p.p.m.v. and 780±850 p.p.m.v. respectively. Scale bars represent 1mm. Note the difference in the coccolith structure (including distinct malformations) and in the degree of calcification of cells grown at normal and elevated CO2 levels.

Adapted from Riebesell, U., I. Zondervan, B. Rost, P. D. Tortell, R. E. Zeebe, and F. M. M. Morel. 2000. Reduced calcification of marine plankton in response to increased atmospheric CO2. Nature 407 :364-367. Reprinted with permission from Nature.