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Ocean Acidification
Lead Author: 

William R Howard¹

Co Authors: Jon Havenhand², Laura Parker³, David Raftos?, Pauline Ross³, Jane Williamson? and Richard Matear?


Howard W.R., Havenhand J., Parker L., Raftos D., Ross, P., Williamson J. and Matear R. (2009) Ocean acidification. In A Marine Climate Change Impacts and Adaptation Report Card for Australia 2009 (Eds. E.S. Poloczanska, A.J. Hobday and A.J. Richardson), NCCARF Publication 05/09, ISBN 978-1-921609-03-9.

Contact Details: 
1 Antarctic Climate & Ecosystems Cooperative Research Centre, Private Bag 80, Hobart, Tas, 7001, Australia.
2 University of Gothenburg, PO Box 100, SE-405 30 Gothenburg, Sweden
3 University of Western Sydney, Penrith South DC, NSW 1797, Australia
4 Department of Biological Sciences, Macquarie University. North Ryde NSW 2109, Australia
5 Marine Ecology Group, Department of Biological Sciences, Macquarie University. Sydney NSW 2109, Australia
6 CSIRO Marine and Atmospheric Research, GPO Box 1538, Hobart, Tas, 7001, Australia

Lead author email: .(JavaScript must be enabled to view this email address)

Download this report in PDF format: OceanAcidfication_2009.pdf

What is happening? What is likely to happen in this century? Addressing knowledge gaps Key adaptation options

Carbon dioxide dissolving in the oceans has lowered pH by 0.1 units since 1750, representing a 30% increase in hydrogen ion (acid) concentration (HIGH confidence)

Ocean pH will decrease by a further 0.2-0.3 units by 2100 (MEDIUM confidence)

Improve projections of the spatial and temporal variability in the progress of acidification and impacts of acidification on marine biodiversity; establish and commit to long-term measurements of ocean chemistry

Climate change requires immediate and vigorous international diplomacy to reduce greenhouse gas emissions. According to the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report, global greenhouse gas emissions have increased by 70% between 1970 and 2004. Some level of future climate change is already certain (e.g. 2°C of warming) because of the greenhouse gases already in the atmosphere. A delay in reducing human-related emissions will result in even greater levels of climate change and subsequent impacts on marine species and habitats.
Adaptation options for marine climate change need to focus on conservation responses to increase resilience of our marine biodiversity as well as adapting our businesses and practices.

Authors >

Will Howard   Ocean Acidification | 


Dr. Will Howard is a research scientist at the Antarctic Climate & Ecosystems Cooperative Research Centre in Hobart, Tasmania. Dr. Howard has a Ph.D in Geological Sciences from Brown University in Providence, Rhode Island, was a U.S. Department of Energy Global Change Distinguished Postdoctoral Fellow, at Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, from 1992-93, and was a lecturer in oceanography at the Sea Education Association, Woods Hole, Massachusetts from 1994-1995, before joining the Antarctic Cooperative Research Centre in Hobart in 1996. He works on marine climate change, with particular emphasis on ocean acidification and its impacts on the past, current, and future ocean. He is particularly interested in the ocean carbon cycle and the responses of marine ecosystems to climate change. His work focuses on the insights into climate change that can be inferred from ocean sediment records as a baseline for pre-industrial conditions and as a tool for understanding the impacts of large-magnitude climate changes of the scale anticipated in the coming centuries. His expertise is in palaeoecology and low-temperature isotopic geochemistry.

Antarctic Climate and Ecosystems Cooperative Research Centre.  Private Bag 80, Hobart TAS 7001, Australia. .(JavaScript must be enabled to view this email address)


David Raftos   Ocean Acidification | 


David Raftos is an Associate Professor of Marine Science at Macquarie University. He has over 25 years experience in marine biology, focusing on the cell and molecular biology of marine invertebrates. After completing his PhD, Associate Professor Raftos worked as a Fulbright Scholar at the University of California Los Angeles, and as an Australian Research Council Fellow at the University of Technology Sydney. He has since held faculty positions at the University of Technology Sydney and Macquarie University, and has also been a Visiting Professor at Cornell University in New York and the George Washington University in Washington DC. Associate Professor Raftos is currently acting as Deputy Chair of the Department of Biological Sciences at Macquarie University and is Co-Director of the University’s Marine Science Program. He is also a senior member of the Sydney Institute of Marine Science and has served on the editorial boards of the Journal of Experimental Zoology and Developmental and Comparative Immunology. His current research focuses on the effects of environmental stress on marine invertebrates at the cellular, protein and genetic levels, with particular emphasis on infectious disease, environmental contamination and climate change. His research projects, funded by the Australian Research Council and the Fisheries Research and Development Corporation, include the use of proteomics and transcriptomics to investigate the biological effects of environmental stress and climate change on marine invertebrates, and molecular studies of disease resistance and susceptibility in oysters. 

Department of Biological Sciences, Macquarie University. North Ryde NSW 2109, Australia. Ph:+61 2 9850 8402.  draftos@rna


Laura Parker   Ocean Acidification | 


Laura Parker is a PhD candidate working on the impacts of climate change and ocean acidification on marine organisms, specifically measuring the impacts on the early life history stages of the Sydney Rock and Pacific Oysters.  Her research is internationally awarded including best oral presentation at “The Effects of Climate Change on the World’s Oceans” International Symposium in Gijon, Spain (2008) and best student oral presentation at the “Oceans in a High CO2 World II” International Symposium in Monaco (2008).  Her work forms part of the signatory in the Monaco Declaration (released 30th January 2009) and has stimulated interest from the NBC, BBC and Australian media.

University of Western Sydney, Penrith South DC, NSW 1797, Australia. .(JavaScript must be enabled to view this email address)


Jane Williamson   Ocean Acidification | 


Dr Jane Williamson completed her BSc at the University of Sydney, then her MSc (Hons) at the University of Auckland, New Zealand. She was awarded her PhD in Marine Biology in 2001 from the University of New South Wales under the supervision of Prof Peter Steinberg. Dr Williamson is now a Senior Lecturer in the Department of Biological Sciences at Macquarie University, Sydney.  She runs the Marine Ecology Group, an interdisciplinary research group with a focus on (1) effects of climate-induced changes on fertilisation, larval development and recruitment of a wide variety of marine invertebrates, (2) ecology and behaviour of marine invertebrates and vertebrates, and (3) aquaculture of edible sea urchins.  Dr Williamson is particularly interested in the effects of ocean acidification, increasing temperature and changes to salinity on early life history stages of marine organisms and the consequences such impacts have to populations and ecosystems. Ultimately, this research will enhance models of the likely effects of climatic changes (through impacts on reproduction) for a range of future CO2 scenarios to help guide policy and management responses.

Marine Ecology Group, Department of Biological Sciences, Macquarie University. Sydney NSW 2109, Australia. Ph: +61 2 9850 8167.  .(JavaScript must be enabled to view this email address)


Richard Matear   Ocean Acidification | 


Richard Matear is a biogeochemical modeller with CMAR’s Climate Adaptation Flagship, with a special interest in understanding the role that the marine carbon cycle plays in controlling atmospheric carbon dioxide (CO2) concentrations, particularly in the Southern Ocean. Present estimates indicate the oceans are removing about 30 per cent of the anthropogenic CO2 emissions, approximately 40% of which occurs in the Southern Ocean. The oceans are expected to continue to absorb large quantities of anthropogenic carbon dioxide, but the extent to which the ocean uptake will be effected by climate change are uncertain. Current research involves the development and implementation of a hierarchy of ocean biogeochemical (BGC) models to model carbon cycling in the ocean, predict oceanic uptake of anthropogenic CO2 and the air-sea exchanges of 12CO2, 13CO2 and O2 into atmospheric transport models. Work by a joint observational and modeling team is aimed at critically comparing the models with observations to assess the BGC model performance. The development and application of BGC models is occurring on the one-dimensional, regional and global scales.

Climate Adaptation Flagship, CSIRO Marine and Atmospheric Research. Hobart TAS 7001, Australia.  .(JavaScript must be enabled to view this email address)


Pauline Ross   Ocean Acidification | 


Associate Professor Pauline Ross of the University of Western Sydney.  Her research interests are in the field of experimental estuarine ecology where she has worked on the influence of larval supply and plant/animal interactions in threatened mangrove, seagrass and saltmarsh habitats.  Her current internationally awarded research with Laura Parker and Wayne O’Connor (Port Stephens Fisheries Centre) is on the impact of elevated CO2 and other multiple stressors (temperature and salinity) on oysters and other estuarine molluscs and the impact of climate change on estuarine habitats. Most recently she completed a review of estuarine molluscs of south-eastern Australia and the impact of anthropogenic factors including climate change on saltmarshes with Todd Minchinton and Winston Ponder (C.S.I.R.O publisher).

University of Western Sydney, Penrith South DC, NSW 1797, Australia. .(JavaScript must be enabled to view this email address)


Jon Havenhand   Ocean Acidification | 


Jon has a PhD from the University of St Andrews, Scotland, and had post-doctoral positions at the Royal Swedish Academy of Sciences and the University of Washington, USA, before taking an appointment at Flinders University, Adelaide, where he helped to establish the Marine Biology and Aquaculture programs.  For the last 8 years Jon has been Professor of Marine Ecology at the Tjärnö Laboratory, University of Gothenburg, Sweden where he is also a core member of the Centre for Marine Evolutionary Biology.  His research on reproductive ecology of marine invertebrates focuses on parental and early life-history traits that can influence adaptation and evolution.  For the last few years he’s been investigating the effects of ocean acidification, temperature, and salinity on fertilization success and larval development.  Jon still works regularly in Australia and has active collaborations with researchers at Macquarie University and the University of Queensland.

University of Gothenburg, Sweden.  .(JavaScript must be enabled to view this email address)


Summary >

Anthropogenic CO2 emissions arise mainly from fossil-fuel combustion, land-use practices, and concrete production during and since the industrial revolution. These emissions first enter the atmosphere, but a large proportion of them are then absorbed into the ocean by physical and biological processes that are normal parts of the natural carbon cycle. The result is more CO2 dissolved in the world’s oceans. The ocean is a weakly-alkaline solution (with a pH of ~ 8.1), but this extra CO2 changes the carbonate chemistry of the surface ocean, driving ocean pH lower. The term ‘ocean acidification’ refers to the fact that the CO2 forms a weak acid (carbonic acid) in water, making the ocean more acidic.

This process of ocean acidification is already underway and discernible in the ocean (Feely et al. 2004). Acidification has lowered the pH of the ocean from its pre-industrial state by about 0.1 pH units. By the end of this century pH levels are likely to drop 0.2 – 0.3 units below pre-industrial pH. The level of atmospheric CO2 is now higher than at any time in at least the past 650,000 years, and probably has not been as high as present levels for 20 million years. The current rate of increase of CO2 in the atmosphere is one hundred times greater than the most rapid increases during major climate changes over the last 650,000 years. Approximately half the fossil-fuel CO2 emitted by man has now dissolved into the ocean.

CO2- driven acidification, in addition to lowering seawater pH, shifts the proportion of dissolved carbon dioxide away from carbonate ion and to bicarbonate ion. It is the carbonate ion that calcium carbonate shell-making organisms require for calcification. Similarly, a range of physiological processes are sensitive to pH itself. Most conclusions about the biological response to ocean acidification in Australian waters come from laboratory manipulations rather than in situ observations. However observational data documenting already-underway changes in calcification in Southern Ocean zooplankton (Moy et al. 2009) and in Great Barrier Reef corals (Cooper et al. 2008, De’Ath et al. 2009) indicate acidification has already begun to have detectable impact on biological processes.

The major scientific knowledge gaps in the physical response lie in projecting the spatial and temporal variability in the progress of acidification. In particular there is a critical need for regional and local-scale data on carbonate chemistry variability and vulnerability. The major scientific knowledge gaps in biological and ecological responses lie in understanding inter-specific and intra-specific differences in response to acidification (“winners” versus “losers”), the resilience of organisms to acidification, and in the implications for the structure of ecosystems.

Scientific Review:

Confidence Assessments >

Observed Impacts: 

Chemical changes to the oceans
High Confidence.  The pH of surface oceans has dropped by 0.1 units since the industrial revolution (Feely et al. 2004).  The carbonate mineral saturation state for calcite and aragonite shows decade-scale downward trend (McNeil et al. 2001; Matear and Lenton 2008; Feely et al. 2004). Pelejero et al. (2005) and Wei et al. (2008) infer historical pH drops in coral archives via coral boron isotope proxy.

Biological changes to the oceans
Medium confidence. Calcification rates in Southern Ocean calcareous zooplankton (foraminifera) have dropped 30-35 % since the pre-industrial times (Moy et al. 2009). Great Barrier Reef corals have reduced calcification rates (De’Ath et al. 2009). Though attribution to ocean acidification alone is unclear (thermal stress is the other likely cause), the pattern is consistent with the expected impact from experimental evidence . Lightly calcified coccolithophorids have shifted ranges poleward in recent years. Though attribution to ocean acidification is unclear, the pattern is consistent with the expected impact (Cubillos et al. 2007).

Low confidence. Calcification in Southern Ocean pteropods has reduced on decadal time scales (Roberts et al. 2008).

Potential Impacts by the 2030s and 2100s: 

Chemical changes to the oceans
Medium Confidence. The pH of surface oceans will drop by 0.2 – 0.3 units by ~ 2100).  The carbonate mineral saturation state for calcite and will continue decade-scale downward trend (Matear and Lenton 2008). In areas of high seasonality such as the high-latitude Southern Ocean aragonite saturation thresholds may be crossed in winter by ~ 2040 (McNeil and Matear 2008). The entire Southern Ocean surface (south of the current Polar Front Zone) will be undersaturated for aragonite by ~ 2100 (Orr et al. 2005). Tropical aragonite saturation states will be low enough to prevent optimal coral growth (Kleypas et al. 1999; Orr et al. 2005). Aragonite saturation horizons will shoal, especially in the Antarctic and Australian southern margins, threatening a wide range of benthic calcifiers (see below).

Biological changes to the oceans
Medium confidence. Calcification rates in Southern Ocean calcareous zooplankton (foraminifera) will continue (e.g. Moy et al. 2009). Great Barrier Reef corals and coralline algae will continue to experience reduced calcification rates (Anthony et al. 2008; De’Ath et al. 2009). Coral growth conditions will deteriorate due to multiple impacts of bleaching and acidification (e.g. Hoegh-Guldberg et al. 2007; Silverman et al. 2009). Mid and high-latitude benthic calcifiers such as deep-water and cold-water corals (Roberts et al. 2006; Maier et al. 2009) coralline algae (Anthony et al. 2008), bryozoans (Smith 2009) and other benthic calcifiers (McClintock et al. 2009) will show reduced calcification and/or increased dissolution as aragonite saturation horizons shoal.

Low confidence. Possible reduction in fertilisation in some marine invertebrates (e.g. Havenhand et al. 2008; Parker et al. 2009). However there is some evidence that temperature will be the major impact on fertilisation (Byrne et al. 2009). Some reef fishes may experience impaired olfactory-based navigation under lower pH (Munday et al. 2008), hindering their ability to find suitable habitats.

1 Recent decline in GBR-wide coral calcification rates is unprecedented in at least the past 400 years. Changes in the marine environment are reducing coral growth rates; and evidence emerging of similar declines from other coral reef regions (e.g. Tanzil et al. 2009)

Adaptation Responses >

The likely peak of atmospheric carbon dioxide levels well above present concentrations, even with emissions-reduction measures, means ocean acidification impacts will be inevitable and marine ecosystem management strategies (e.g. marine protected areas) will have to factor in some acidification impacts.

Policy Challenge
Ocean acidification presents some unique policy as well as scientific challenges. Ocean acidification differs from global warming in that its impact derives from the chemistry of carbon dioxide (CO2) in seawater, rather than from its physical action as a greenhouse gas in the atmosphere. This means that increasing atmospheric CO2 will inevitably increase ocean acidity, largely independent of the rate of global warming and its impacts, and independent of climate-model projections. Ocean acidification will need to be considered in the context of setting stabilisation targets for atmospheric CO2 and the timelines on which the targets need to be reached. There are natural time lags involved in the marine carbon cycle, both in the uptake of CO2 by the ocean as well as in the centuries needed to reverse the acidification already under way. These lags place a penalty on delaying limits on carbon emissions and a premium on early action. A further policy challenge arises because the only mitigation option available is a reduction in carbon dioxide emissions. The thresholds for atmospheric CO2 levels at which acidification impacts begin may differ from those which trigger warming impacts (e.g. McNeil and Matear 2008), so mitigating acidification may require different emissions-limitation targets than global warming. Similarly, because acidification arises only from CO2 emissions, limiting other greenhouse gases (such as nitrous oxide) will not mitigate ocean acidification.

Knowledge Gaps >

The major scientific knowledge gaps in the physical response lie in projecting the spatial and temporal variability in the progress of acidification. In particular there is a critical need for regional and local-scale data on carbonate chemistry variability and vulnerability. The major scientific knowledge gaps in biological and ecological responses lie in understanding inter-specific and intra-specific differences in response to acidification (“winners” versus “losers”), the resilience of organisms to acidification, and in the implications for the structure of ecosystems. In addition there is a critical need for research into the effect of multiple stressors, especially the combined impacts of likely environmental changes such as expansion of hypoxic zones and increased temperature.
Further Information >

The research of the authors has been supported by a number of funding and research agencies, including DCC, CSIRO, and the Antarctic Climate & Ecosystems Cooperative Research Centre.

References >

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Byrne, M., Ho, M., Selvakumaraswamy, P., Nguyen, H.D., Dworjanyn, S.A. and Davis, A.R. (2009) Temperature, but not pH, compromises sea urchin fertilization and early development under near-future climate change scenarios. Proceedings of the Royal Society B: Biological Sciences 276: 1883-1888, doi:10.1098/rspb.2008.1935
Cooper, T.F., De’Ath, G., Fabricius, K.E. and Lough, J.M. (2008) Declining coral calcification in massive Porites in two nearshore regions of the northern Great Barrier Reef. Global Change Biology 14: 529-538.
Cubillos, J.C., Wright, S.W., Nash, G., de Salas, M.F., Griffiths, B., Tilbrook, B., Poisson, A. and Hallegraeff, G. M. (2007) Calcification morphotypes of the coccolithophorid Emiliania huxleyi in the Southern Ocean: changes in 2001 to 2006 compared to historical data. Marine Ecology Progress Series 348: 47-54.
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