Ocean Acidification : Understanding the Other Climate Crisis 7-1-2016 Ocean Acidification : The Other CO 2 Problem ?

Rising atmospheric carbon dioxide (CO2), primarily from human fossil fuel combustion, reduces ocean pH and causes wholesale shifts in seawater carbonate chemistry. The process of ocean acidification is well documented in field data, and the rate will accelerate over this century unless future CO2 emissions are curbed dramatically. Acidification alters seawater chemical speciation and biogeochemical cycles of many elements and compounds. One well-known effect is the lowering of calcium carbonate saturation states, which impacts shell-forming marine organisms from plankton to benthic molluscs, echinoderms, and corals. Many calcifying species exhibit reduced calcification and growth rates in laboratory experiments under high-CO2 conditions. Ocean acidification also causes an increase in carbon fixation rates in some photosynthetic organisms (both calcifying and noncalcifying). The potential for marine organisms to adapt to increasing CO2 and broader implications for ocean ecosystems are not well known; both are high priorities for future research. Although ocean pH has varied in the geological past, paleo-events may be only imperfect analogs to current conditions. INTRODUCTION .................................................................... 213 OCEAN CARBONATE SYSTEM ............................................ 217 BIOLOGICAL RESPONSES TO ACIDIFICATION ............... 219 Shallow-Water Tropical Corals and Coral Reefs ........... 220 Deep-Water Corals and Carbonate Mounds.................. 223 Other Benthic Invertebrates ......................................... 224  Reproduced with permission from the Annual Review of Marine Science, Volume 1 © 2009 by Annual Reviews, http://www.annualreviews.org, Annu. Rev. Mar. Sci. 2009. 1:169–92. First published online as a Review in Advance on August 29, 2009. This article’s doi: 10.1146/annurev.marine.010908.163834.  Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543; email: sdoney@whoi.edu  Department of Biological Sciences, California State University, San Marcos, California 92096; email: fabry@csusm.edu † Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, Washington 98115; email: Richard.A.Feely@noaa.gov  Institute for the Study of Society and Environment, National Center for Atmospheric Research, Boulder, Colorado 80307; email: kleypas@ucar.edu 1 Doney et al.: Ocean Acidification: The Other CO2 Problem? Published by UW Law Digital Commons, 2019 2016] OCEAN ACIDIFICATION: THE OTHER CO2 PROBLEM 213 Planktonic Calcification ................................................. 225 Primary Production and Nitrogen Fixation .................. 226 ECOLOGICAL AND BIOGEOCHEMICAL IMPACTS .......... 228 Food Webs and Ecosystems ........................................... 228 Oceanic CaCO3 Budget .................................................. 229 Carbon and Nutrient Cycling ........................................ 231 Chemical Speciation in Seawater .................................. 232 GEOLOGICAL AND HISTORICAL EVIDENCE ................... 233 DISCLOSURE STATEMENT ................................................. 237 ACKNOWLEDGMENTS ......................................................... 238 LITERATURE CITED ............................................................. 238 INTRODUCTION Over the past 250 years, atmospheric carbon dioxide (CO2) levels increased by nearly 40%, from preindustrial levels of approximately 280 ppmv (parts per million volume) to nearly 384 ppmv in 2007 (Solomon et al. 2007). This rate of increase, driven by human fossil fuel combustion and deforestation, is at least an order of magnitude faster than has occurred for millions of years (Doney & Schimel 2007), and the current concentration is higher than experienced on Earth for at least the past 800,000 years (Lüthi et al. 2008). Rising atmospheric CO2 is tempered by oceanic uptake, which accounts for nearly a third of anthropogenic carbon added to the atmosphere (Sabine & Feely 2007, Sabine et al. 2004), and without which atmospheric CO2 would be approximately 450 ppmv today, a level of CO2 that would have led to even greater climate change than witnessed today. Ocean CO2 uptake, however, is not benign; it causes pH1 reductions and alterations in fundamental chemical balances that together are commonly referred to as ocean acidification. Because climate change and ocean acidification are both caused by increasing atmospheric CO2, acidification is commonly referred to as the “other CO2 problem” (Henderson 2006, Turley 2005). Ocean acidification2 is a predictable consequence of rising atmospheric CO2 and does not suffer from uncertainties associated with climate change forecasts. Absorption of anthropogenic CO2, reduced pH, and lower calcium carbonate 1. pH: a measure of ocean acidity and hydrogen ion H+ concentration; pH 