Victoria J. Fabry

A safe operating space for humanity

Identifying and quantifying planetary boundaries that must not be transgressed could help prevent human activities from causing unacceptable environmental change, argue Johan Rockstrom and colleagues.

Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms

Todays surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms—such as corals and some plankton—will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of the ocean–carbon cycle to assess calcium carbonate saturation under the IS92a ‘business-as-usual’ scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously.

Ocean acidification: the other CO2 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.

Ocean Acidification and Its Potential Effects on Marine Ecosystems

Ocean acidification is rapidly changing the carbonate system of the world oceans. Past mass extinction events have been linked to ocean acidification, and the current rate of change in seawater chemistry is unprecedented. Evidence suggests that these changes will have significant consequences for marine taxa, particularly those that build skeletons, shells, and tests of biogenic calcium carbonate. Potential changes in species distributions and abundances could propagate through multiple trophic levels of marine food webs, though research into the long‐term ecosystem impacts of ocean acidification is in its infancy. This review attempts to provide a general synthesis of known and/or hypothesized biological and ecosystem responses to increasing ocean acidification. Marine taxa covered in this review include tropical reef‐building corals, cold‐water corals, crustose coralline algae, Halimeda, benthic mollusks, echinoderms, coccolithophores, foraminifera, pteropods, seagrasses, jellyfishes, and fishes. The risk of irreversible ecosystem changes due to ocean acidification should enlighten the ongoing CO2 emissions debate and make it clear that the human dependence on fossil fuels must end quickly. Political will and significant large‐scale investment in clean‐energy technologies are essential if we are to avoid the most damaging effects of human‐induced climate change, including ocean acidification.

Guide to best practices for ocean acidification research and data reporting

Ocean acidification is an undisputed fact. The ocean presently takes up one-fourth of the carbon CO2 emitted to the atmosphere from human activities. As this CO2 dissolves in the surface ocean, it reacts with seawater to form carbonic acid, increasing ocean acidity and shifting the partitioning of inorganic carbon species towards increased CO2 and dissolved inorganic carbon, and decreased concentration of carbonate ion. While our understanding of the possible consequences of ocean acidification is still rudimentary, both the scientific community and the society at large are increasingly concerned about the possible risks associated with ocean acidification for marine organisms and ecosystems. As this new and pressing field of marine research gains momentum, many in our community, including representatives of coordinated research projects, international scientific organisations, funding agencies, and scientists in this field felt the need to provide guidelines and standards for ocean acidification research. To initiate this process, the European Project on Ocean Acidification (EPOCA) and the International Oceanographic Commission (IOC) jointly invited over 40 leading scientists active in ocean acidification research to a meeting at the Leibniz Institute of Marine Science (IFM-GEOMAR) in Kiel, Germany on 19-21 November 2008. At the meeting, which was sponsored by EPOCA, IOC, the Scientific Council on Oceanic Research (SCOR), the U.S. Ocean Carbon and Biogeochemistry Project (OCB) and the Kiel Excellence Cluster “The Future Ocean”, the basic structure and contents of the guide was agreed upon and an outline was drafted. In the following months, the workshop participants and additional invited experts prepared draft manuscripts for each of the sections, which were subsequently reviewed by independent experts and revised according to their recommendations. Starting 15 May 2009, the guide was made publicly available for an open community review.

Marine Calcifiers in a High-CO2 Ocean

New results show that the response of marine organisms to ocean acidification varies both within and between species.

Comment on "Phytoplankton Calcification in a High-CO2 World"

Iglesias-Rodriguez et al. (Research Articles, 18 April 2008, p. 336) reported that the coccolithophore Emiliania huxleyi doubles its organic matter production and calcification in response to high carbon dioxide partial pressures, contrary to previous laboratory and field studies. We argue that shortcomings in their experimental protocol compromise the interpretation of their data and the resulting conclusions.

Present and future changes in seawater chemistry due to ocean acidification

The oceanic uptake of anthropogenic CO 2 changes the seawater chemistry and potentially can alter biological systems in the upper oceans. Estimates of future atmospheric and oceanic CO 2 concentrations, based on the Intergovernmental Panel on Climate Change (IPCC) emission scenarios, indicate that atmospheric CO 2 levels could approach 800 ppm by the end of the century. Corresponding models for the oceans indicate that surface water pH would decrease by approximately 0.4 pH units, and the carbonate ion concentration would decrease by as much as 48% by the end of the century. The surface ocean pH would be lower than it has been for more than 20 million years. Such changes would significantly lower the oceans buffering capacity, which would reduce its ability to accept more CO 2 from the atmosphere. Recent field and laboratory studies reveal that the carbonate chemistry of seawater has a profound impact on the calcification rates of individual species and communities in both planktonic and benthic habitats. The calcification rates of nearly all calcifying organisms studied to date decrease in response to decreased carbonate ion concentration. In general, when pCO 2 was increased to twice preindustrial levels, a decrease in the calcification rate ranging from about ―5% to ―60% was observed. Unless calcifying organisms can adapt to projected changes in seawater chemistry, there will likely be profound changes in the structure of pelagic and benthic marine ecosystems.

Comment on "Modern-age buildup of CO2 and its effects on seawater acidity and salinity" by Hugo A. Loaiciga

A doubling of present atmospheric CO2 concentrations (to 760 ppm) may occur by the end of this century in the absence of efforts to diminish CO2 emissions from fossil-fuel combustion [Intergovernmental Panel on Climate Change (IPCC), 2001]. Based on inappropriate assumptions and erroneous thermodynamic calculations, Loa´ iciga [2006] mistakenly reports that atmospheric CO2 concentrations of 760 ppm will lower the pH of the surface ocean by 0.28 relative to the natural ‘‘mid 18th century’’ conditions. He implies that a drop of this magnitude will have minimal biological impact, neglecting numerous recent experiments and observations showing that this decrease in pH would substantially affect the physiology and health of marine organisms. Here, we focus on two fundamental flaws in the published analysis that invalidate his conclusions: (1) he assumes instantaneous chemical equilibration of the ocean with carbonate minerals although this process is known to take five to ten thousand years and (2) contrary to what is implied by Loa´iciga, many marine organisms are sensitive to a pH decrease of 0.2 units.

Ocean Acidification's Effects on Marine Ecosystems and Biogeochemistry: Ocean Carbon and Biogeochemistry Scoping Workshop on Ocean Acidification Research; La Jolla, California, 9–11 October 2007

Rising atmospheric carbon dioxide (CO2) concentration is causing global warming and ocean acidification. Nearly one third of the total anthropogenic CO2 produced in the past 200 years has been taken up by the oceans. While oceanic uptake of anthropogenic CO2 may lessen the extent of global warming, evidence suggests that effects of anthropogenic CO2 on ocean chemistry have profound consequences for marine organisms, potentially altering ecosystem structure, food webs, and biogeochemical processes. An assemblage of 93 scientists participated in a 3-day workshop to develop research strategies that address present and future ocean acidification impacts. The Ocean Carbon and Biogeochemistry program (http://www.us-ocb.org) sponsored this workshop, with support from the U.S. National Science Foundation, National Oceanic and Atmospheric Administration, NASA, U.S. Geological Survey, and Scripps Institution of Oceanography.