The cool twin of carbon dioxide gets some worthy attention

7 June 2023

Carbon dioxide (CO₂) has been a headliner for many years but did you know that there is another important climate gas  that rarely gets mentioned?

Dimethylsulfide (DMS) is produced mainly by phytoplankton and bacteria and is the most abundant biological sulfur compound emitted from the ocean to the atmosphere, contributing to the distinctive smell of the sea. Once in the atmosphere, DMS plays a key part in the production and growth of atmospheric sulfate aerosols that influence the radiative properties of clouds, and ultimately affects Earth’s climate.

The natural climate cooling effect of DMS is estimated to be of a similar magnitude to the warming that has been driven by human CO₂ emissions, although the overall climate warming from increasing CO₂ will always outweigh any cooling. Nevertheless, DMS is considered a crucial player in the delicate balance of Earth’s climate and is worthy of attention.

Due to the challenges of measuring DMS, the intricate biological processes involved in its production, and the complex role of aerosols in climate regulation, this vital trace gas is still crudely represented in climate models. As a result, there is much more uncertainty concerning the climate influence of DMS, compared to the well-understood role of CO₂.

This comprehensive review of DMS research, published in Nature Reviews Earth & Environment, emphasises the urgent need for a greater scientific focus on unraveling the key biological processes controlling DMS production and understanding its role in climate regulation, as well as improving the accuracy of DMS flux and climate models.

The paper, led by Plymouth Marine Laboratory in partnership with Bigelow Laboratory for Ocean Sciences (USA) and the University of East Anglia, also highlights other areas that would benefit from a more robust comprehension of DMS. These include studying the effects of multiple stressors on the biological production of DMS, and evaluating how climate change mitigation strategies might influence DMS production, which would again feed in to improving the accuracy of climate models.

There is significantly more data available on CO₂ sources and sinks, leading to a vastly better understanding of how oceanic CO₂ uptake impacts climate. When comparing CO₂ sampling with DMS, up to 40 million CO₂ measurements have been made across the global oceans since 1957, whereas DMS has only ever been sampled about 1 million times, with many large areas of ocean completely unsampled.

The challenges in regularly measuring DMS centers mainly around technology. Autonomous CO₂ measuring devices can be installed on almost any seagoing vessel, whereas DMS sampling equipment is much less autonomous, with lower sampling frequency and often needing a trained expert to operate. This greatly reduces opportunities for data collection. However, in recent years the technology has been catching up and DMS measurements can now be made at much higher frequency, resulting in greater global data coverage.

The team emphasize the need for the development of low-cost, low-energy autonomous DMS sensors for deployment on buoys or unmanned vehicles to target under-sampled regions or capture sporadic events such as dust-stimulated algal blooms, which could increase the amount of DMS being produced.

A second issue for DMS research is the type of data that has been collected. Genetics and molecular biology-based techniques have revealed the multitude of marine microorganisms that are capable of influencing global DMS production. However, there are limitations and challenges in using this information, as molecular data only highlights the potential for changes in seawater DMS concentrations, and often lacks useful accompanying measurements of DMS production and cycling. Future research must be interdisciplinary to ensure that the most useful DMS data is collected and integrated into the developing knowledge base.
 
Dr Frances Hopkins, lead author on the review paper and Marine Biogeochemist at Plymouth Marine Laboratory, commented:
 
“DMS is a fascinating and important marine trace gas, yet we simply do not know enough about it. We need a global long-term sampling programme specifically for DMS to help fill these critical data gaps and help us gain a better understanding of key processes.”
 
“This is the first comprehensive review on DMS biogeochemistry research for over 10 years so we hope this will be a valuable resource for anyone doing research on seawater sulfur and/or marine aerosols.”
 

Related information

Full paper: The biogeochemistry of marine dimethylsulfide