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Acidifying oceans may threaten crucial links in Earth’s climate cycles

13 May 2020

A review of more than two hundred studies highlights where research needs to focus if we are to understand vital oceanic processes that can alter the Earth’s climate.

Ocean surface

Marine trace gases like dimethyl sulfide, nitrous oxide and ammonia can move between the sea and the atmosphere at the surface of the ocean. These fluxes allow a transfer of essential elements from sea to land and, importantly, an exchange of substances that can influence the chemistry of the atmosphere and climate.
Many of these marine trace gases are biogenic, the product of living organisms – being directly or indirectly produced by bacteria, phytoplankton and seaweeds – and their production is likely to be affected by stressors including ocean acidification. Changes in production could have important effects on the air-sea flux of trace gases, which play important roles in processes that influence our climate. Some behave as greenhouse gases, having a warming effect on the atmosphere, whilst others influence the production of ‘cloud-seeding’ particles which can have a climate cooling effect.

The recent study, led by Plymouth Marine Laboratory and scientists from 16 of the world’s leading marine research institutes, focused particularly on how trace gas production is affected by ocean acidification, which lowers ocean pH towards the more acidic end of the scale.

Dr Frances Hopkins, lead author and PML Marine Biogeochemist, said: “This paper came out of a UN-GESAMP (United Nation Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection)-funded workshop, which brought together the world-leading experts in this field. It provided us the opportunity to pull together more than 15 years of research to clarify the current state-of-knowledge and highlight where future research is needed”.

Building understanding is made harder by the need to consider both direct and indirect effects of ocean acidification, with the latter particularly tricky to pin down, and the other climate change stressors – such as warming, deoxygenation and eutrophication – that are also likely to have an effect.

Crucially, the study found a need for more basic information around the processes that drive trace gas production and cycling. This cycling is incredibly complex, so understanding the effects of ocean acidification requires looking at many factors involved, such as phytoplankton species, bacterial processes, and effects of marine organisms grazing. A better knowledge of these processes would also aid in developing Earth system models, which can help to predict future trace gas production and emissions, and related climate effects.

When planning experiments in this area, short-term studies can find out how organisms at the ocean surface have adapted to carbonate chemistry fluctuations and might adapt in future, affecting associated trace gas production. But longer term studies, over multiple generations, would indicate how planktonic communities might evolve to cope with ocean acidification and other climate-driven stressors. 

Additionally, in order to build a full picture of how organisms react to changing conditions, and how this impacts on trace gas production, scientists need to research natural communities out in the field as well as model organisms in the laboratory.

Complex studies that allow for all of these elements to be considered require significant collaboration, funding, and a multi-disciplinary approach. By understanding where knowledge is lacking, researchers can work to fill in the gaps and develop this crucial field of study.

Dr Hopkins said: “Changes to the oceans caused by human activities, like ocean acidification, have the potential to impact the vital processes that control trace gas production. For example, we have a solid evidence base suggesting that the key climate-cooling gas dimethyl sulfide (DMS) may be significantly affected by ocean acidification. Some of these data have been integrated into models, which demonstrate that these changes could significantly affect global temperature and climate." 

We now need to design and perform more studies to further unravel the effects of ocean acidification on production of DMS and other marine trace gases, improving our ability to predict Earth’s climate into the future”.

The study brought together researchers from around the world, at PML, University of East Anglia, Le Laboratoire des Sciences du Climat et de l’Environnement, University of Bristol, Bigelow Laboratory for Ocean Sciences, École normale supérieure, Texas A&M University System, Bjerknes Centre for Climate Research, University of Malaya, National Institute of Water and Atmospheric Research Wellington, Pohang University of Science and Technology, Universite Laval, and CSIR - National Institute of Oceanography.

Related information

'The impacts of ocean acidification on marine trace gases and the implications for atmospheric chemistry and climate' is published open access in Proceedings of the Royal Society A