The other CO2 problem

Ocean acidification is often called “the other CO2 problem”.

While most of us are familiar with carbon dioxide (CO2) emissions contributing to global warming, less commonly known is ocean acidification: the ability of CO2 to change the chemistry of our ocean. Basically, the ocean absorbs plenty of our CO2 emissions which leads to a lowering of the ocean's pH level. This makes the ocean a more acidic environment, which ultimately has severe impacts on marine life.

The newly released Intergovernmental Panel on Climate Change (IPCC) report states that changes to deep ocean acidification are irreversible in timescales of hundreds and thousands of years. With increasing CO2 emissions, the oceans’ ability to absorb CO2 becomes less and less effective, leaving more CO2 in the atmosphere, in turn accelerating global warming.

Coral reefs

Photograph by Greg Lecoeur, Nat Geo Image Collection

At some point in their lives, nearly a quarter of all marine species are reliant on coral reefs. Coral reefs provide an important habitat and home for a wide array of fish species. Coral reefs build their limestone structures (CaCO3) from carbonate ions floating in the sea. However, ocean acidification considerably reduces accessibility to these building blocks, leading their structures to disintegrate. Without a home to return to, fish species and important marine life will decline in diversity.

CLOWN FISH

Clownfish among numerous other marine species rely on their auditory senses to get an understanding of their environment and other species around them. A study on young clownfish found that clownfish raised in current day oceanic CO2 levels would swim away from noisy reefs to evade predators. Contrastingly, clownfish raised in CO2 rich waters projected by the IPCC found that the clownfish did not swim away upon hearing predatory noises. Losing the ability to hear properly could have detrimental impacts on survival of fishes from predation.

sea snails

Sea snails, often called butterflies of the ocean, are small free-living oceanic snails that live in the open water, providing an essential food source to many fish we consume, such as salmon and herring. However, their shells are fragile, and start to dissolve in acidified oceans, even compromising their swimming. Due to the composition of their frail shells, they are considered an early warning signal of ocean acidification. There have already been spotted individuals in acidified waters with signs of dissolution such as white spots, lines and etching.

Photographs by Steve Ringman, NOAA

Image on the left shows a sea snail in normal oceanic pH, whereas the sea snail on right shows signs of shell dissolution from ocean acidification

LOOKING FORWARD

There are many uncertainties surrounding ocean acidification and how ocean ecosystems will fare in the future. Will species prove to be more resilient than thought, and adapt? What are some of the unforeseen impacts that we have yet to discover? How can we as humans reverse our impacts in a sustainable way that helps our planet and its inhabitants? There will be many questions to tackle in the years to come, and hopefully the COP26 negotiations will take our ocean seriously!

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sources and further reading:

• Video of ocean acidification on sea snail: https://www.youtube.com/watch?v=6H_VDhXiFk4

Grey literature

• https://www.nationalgeographic.co.uk/environment-and-conservation/2020/06/scientists-are-trying-to-save-coral-reefs-heres-whats-working

• https://www.nationalgeographic.com/science/article/will-we-ever-lose-all-our-corals

• https://www.nationalgeographic.com/news/2014/5/140502-ocean-snail-shell-dissolving-acidification-climate-change-science

• https://research.noaa.gov/article/ArtMID/587/ArticleID/1133/NOAA-led-researchers-discover-ocean-acidity-is-dissolving-shells-of-tiny-snails-off-West-Coast

Primary literature

1. Bednaršek, N., et al. (2016). Pteropods on the edge: Cumulative effects of ocean acidification, warming, and deoxygenation. Progress in oceanography 145 1-24.

2. Doney, S.C., Fabry, V.J., Feely, R.A. and Kleypas, J.A. (2009) Ocean acidification: the other CO2 problem. Annu. Rev. Mar. Sci. 1,169–92

3. Hoegh-Guldberg, O., Mumby, P.J., Hooten, A.J., Steneck, R.S., Greenfield, P., Gomez, E., Harvell, C.D., Sale, P.F., Edwards, A.J., Caldeira, K. and Knowlton, N., 2007. Coral reefs under rapid climate change and ocean acidification. science, 318(5857), pp.1737-1742.

4. IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [MassonDelmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press.

5. Sweetman, A.K., Thurbur, A.R., Smith, C.R., et al. (2017). Major impacts of climate change on deep-sea benthic ecosystems. Elem Sci Anth, 5(4)

6. Simpson, S. D., Munday, P. L., Wittenrich, M. L., Manassa, R., Dixson, D. L., Gagliano, M., & Yan, H. Y. (2011). Ocean acidification erodes crucial auditory behaviour in a marine fish. Biology Letters (2005), 7(6), 917–920. https://doi.org/10.1098/rsbl.2011.0293