Ocean acidification, and why it’s important
The acidity of the world’s oceans is rising likely faster than at any time during the past 55 million years, primarily due to greater amounts of carbon dioxide (CO2) in the atmosphere.
CO2 is absorbed by seawater, reducing its pH level (i.e., increasing its acidity), which in turn influences many important chemical and biological processes. Although acidification will not actually make seawater acidic (that is, with a pH level below 7), CO2 does lower its calcium carbonate saturation state. This measures the chemical propensity of seawater to become potentially corrosive to calcium carbonate, which many marine organisms use to build shells or skeletons.
As well as affecting the ability of some marine organisms to form shells, ocean acidification can affect plant and animal development, their behavior and, indirectly, the quality and availability of food.
The biological effects of ocean acidification are difficult to assess, especially because this process is taking place at the same time as other major changes, such as ocean warming, oxygen depletion and, at high latitudes, sea ice loss. Laboratory experiments and field observations show a wide range of direct and indirect effects of acidification, some negative and some positive.
However, despite difficulties in isolating its effects, ocean acidification, alongside other ecosystem stressors, is likely to affect the abundance and distribution of fish stocks and marine animals of commercial and cultural importance to communities in the Arctic and beyond.
The developing science
Our scientific understanding of ocean acidification is deepening as more data are collected relating to the chemistry of the Arctic Ocean and the responses of marine organisms. In addition, models used to project future conditions and impacts continue to be refined. This latest assessment builds on the previous one by reviewing and synthesizing research published over the last five years relating to the marine chemistry of acidification and to its biological impacts, supplemented by older studies where newer research has not been carried out
Arctic Ocean acidification
The acidification of the Arctic Ocean is increasingly evident, with continued observations showing a rapidly changing marine carbonate system. However, high natural variability of the carbonate system makes it difficult to obtain a clear picture of acidification in the Arctic Ocean. It is influenced by the seasons, driven by a complex interplay between seasonal biological production, temperature variability, freshwater supply and ice cover. Despite this natural variability, projections suggest that, with ongoing net carbon emissions, Arctic Ocean acidification will continue over the remainder of this century.
In addition to absorption of CO2 from the atmosphere, ocean acidification is also driven by the decomposition of organic (i.e., carbon-containing) matter fed into the ocean from rivers, and by the oxidation of methane (CH4) from thawing subsea permafrost. This methane oxidation has the potential to cause rapid and massive ocean acidification.
In some areas of the ocean, particularly in relatively shallow coastal shelves, these processes currently play a much more important role than that of atmospheric CO2 in determining the rate and extent of ocean acidification. In some regions of the Siberian shelf, for example, decaying organic matter from thawing subsea permafrost and from river run-off results in marine CO2 concentrations that are well above even those levels expected in the atmosphere by the end of the century.
These processes influence relatively high pH water that enters the Arctic Ocean from the North Atlantic, which is then mixed with lower pH water that flows in from the Pacific. This modified Arctic water then flows out into the North Atlantic through the Canadian Arctic Archipelago and the Fram Strait. The regions of the North Atlantic that are influenced by these outflows are both biologically productive and support important commercial fi sheries. Accelerated acidification as the result of enhanced atmospheric CO2 uptake and the decomposition of organic matter within the Arctic Ocean thus has the potential to impact not only the ecosystems of the central Arctic Ocean, but also ecosystems downstream in the North Atlantic.
The biological response
Ocean acidification is likely to affect Arctic organisms and ecosystems to an extent that human societies that exploit or depend on them will be harmed.
Responses of marine life to acidification are likely to be complex and situation specific. While many organisms are expected to be negatively affected, some may benefit. Also, the magnitude and perhaps even direction of these responses will depend upon other features of the organism and its habitat, such as its lifestage, location, and season.
Changes to individual species will potentially change interactions between species, shifting the balance of ecosystems away from their current condition. For example, ocean acidification may favor some non-calcifying algae, changing pelagic ecosystems and shifting benthic habitats from coralline algae, and the kelp they facilitate, to simple mat-algae dominated ecosystems. Changes to lower-level organisms such as bivalves or mollusks could have cascading effects through the food chain and affect predators such as Pacific walrus and bearded seals.
Adaptation through natural selection is likely to be greatest among species with large populations, which benefit from greater genetic variation, and those species with short generation times. However, it is unclear whether adaptation in Arctic species will be rapid enough in the context of rapid forecasted ocean acidification.
Exploring the socio-economic effects of ocean acidification
The Arctic and subarctic regions are home to important and valuable fisheries. They yield a tenth of the global commercial catch, and subsistence fisheries provide vital nutritional and cultural services to Arctic residents. Ocean acidification threatens these fisheries, both directly, by altering the growth, development or behavior of marine life, and indirectly, by altering foodwebs and predator-prey relationships. The future effects of ocean acidification will not be uniform across the region, nor can they be reliably predicted.
Future ocean acidification, in combination with other environmental stressors, particularly ocean warming, is likely to be sufficient to cause changes in Arctic organisms and ecosystems to an extent that will affect communities that depend upon them. An additional issue is the influence that socio-economic trends, such as developments in global seafood markets, will have in determining the future value of Arctic fisheries.
Case Study: Alaska's fishery sector
Important commercial, subsistence and recreational fisheries in Alaska are found in environments facing rapid change, particularly in terms of temperature and acidification. However, prior to the case studies in this assessment, end-to-end studies of how changes in seawater chemistry could affect resources of importance to specific communities have not, to date, focused on Alaska or other high-latitude regions. In this case study, researchers developed an index to measure risk faced by different regions within Alaska from ocean acidification. It combined hazard, assessed in terms of changes to ocean chemistry, exposure, in terms of the importance of certain marine species to human communities, and vulnerability, in terms of human reliance on a given species, and the ability of societies to adapt effectively to their decreased availability.
- Many of the marine organisms likely to be most affected by ocean acidification, such as mollusks, are important to both highly productive commercial fisheries and to traditional subsistence ways of life.
- The impacts of ocean acidification are uneven: southern Alaska faces the greater risk, due to its dependence on susceptible species for nutrition and income, the forecasted rapid change in chemical conditions and, as a rural area, its low job diversity, employment, and education levels, as well as its high food costs.
- Studies that combine scientific and socio-economic data provide a means of identifying threats to communities from environmental change, and can help them to develop strategies to reduce risks and to adapt.
- Measuring vulnerability at the local level can help to understand the regional processes at work, and support the development of localized policies to reduce risk.
- A detailed look at the red king crab fishery in Bristol Bay found that acidification is expected to cause a long-term decline in the harvest, with direct and indirect economic consequences, although the precise effects will also be greatly influenced by world market demand.
1. Address the causes
- Ocean acidification and its impacts will worsen if greenhouse gas emissions continue at their present rate. The Arctic Council should urge the Arctic States, Observer states, and the international community to reduce emissions of greenhouse gases as a matter of urgency.
2. Enhance research
- The effects of ocean acidification, in combination with other stressors such as warming, are highly uncertain. That uncertainty is compounded when other environmental, social and economic responses and trends are also considered. There is a need for multi-stressor research into how Arctic species are likely to respond.
- Ecosystem changes should be monitored in such a way that allows for the identification and differentiation of the impact of each stressor on the ecosystem, as well as the potential synergistic effects of multiple combined stressors.
- Monitoring should also be intensified in the North Atlantic, given the biological, commercial and subsistence importance of fisheries in these waters and the impact of outflow of increasingly acidified water from the Arctic Basin. Regional fishery management organizations, OSPAR and the Arctic Council should cooperate to do so.
- There is a need for more Arctic-specific research into ocean acidification and its effects, whether regarding impacts on species, habitats or economic consequences. Currently, the lack of such research means many findings are extrapolated from research undertaken experimentally or in other geographic regions.
- Indigenous knowledge, and traditional and local knowledge has been included in this assessment to a limited extent, and future work would benefit from increased involvement of communities in monitoring and research projects.
- There is a need for research into longer-term responses of Arctic species and ecosystems to ongoing environmental change. Laboratory research and in situ monitoring of physiological responses and genetic adaptation will be key to improving predictions of these responses over time.
- Encouraging appropriate bodies to conduct research and monitoring of Arctic Ocean acidification must continue to be a high priority for messaging from the Arctic Council. Cooperation between Arctic countries and with other relevant organizations such as OSPAR and ICES would also be helpful.
3. Build resilience
- A lack of certainty about the interplay between biological changes and social and economic impacts of ocean acidification should not preclude action. Actions on resilience should be directed towards providing communities with flexibility, adaptability and economic and ecological adaptation in the face of change and uncertainty.
- There is need for a unified monitoring program to support adaptation actions in the Arctic and also to provide Arctic communities with the tools and training to conduct local, unified research and monitoring.
- There is a need for more scientific research on Arctic fisheries and flexible and adaptive fishery management regimes that can respond both to the effects of acidification and to the migration of fish stocks due to warming and other environmental changes.
- Studies that integrate science and socio-economics can help communities identify threats posed by environmental changes, and develop strategies to adapt. Local communities should develop resilience strategies with the support of policymakers, targeted scientific research, Indigenous knowledge, and traditional and local knowledge. These might include policies that promote economic diversification, and provide job training and educational opportunities, as well as increased access to alternative sources of protein to reduce regional risk levels.