A first-of-its-kind study reveals that the world’s oceans emit a sulfur gas that has a more significant cooling effect on the climate than previously understood, particularly over the Southern Ocean. The findings, published in Science Advances, show that oceans not only absorb and redistribute solar heat, but also produce gases that significantly influence climate change, such as by enhancing the brightness of clouds to reflect heat back into space.
The study sheds new light on the climatic role of marine sulfur, by identifying a previously undetected gas, methanethiol. It was challenging to measure this gas in the past, and previous research mostly focused on warmer oceans, while polar oceans emerged to be the main emission sites. The discovery of methanethiol has been a significant breakthrough in understanding the role of oceans in regulating Earth’s climate—a concept proposed over 40 years ago.
The research was led by a team from Spain’s Institute of Marine Sciences (ICM-CSIC) and the Blas Cabrera Institute of Physical Chemistry (IQF-CSIC), including Dr Charel Wohl, now at the University of East Anglia (UEA) in the UK. According to their findings, microscopic ocean-dwelling plankton produce a sulfur gas, dimethyl sulfide, which oxidizes in the atmosphere to form aerosols. These aerosols reflect solar radiation back into space, reducing Earth’s heat retention and enhancing cloud formation, significantly cooling the planet.
This new understanding of the climatic role of methanethiol better illustrates the crucial significance of sulfur aerosols in regulating the planet’s climate. It also underscores the immense impact human activities have on the climate and warns of continued global warming if no action is taken.
Dr Wohl, from UEA’s Centre for Ocean and Atmospheric Sciences and a lead author of the study, said, “We knew methanethiol was being released from the ocean, but we didn’t know how much, where, or its impact on the climate. Climate models have greatly overestimated the solar radiation reaching the Southern Ocean, primarily due to inaccuracies in simulating clouds. Our work helps bridge this knowledge gap between models and actual observations.”
The team’s findings allow for a more accurate representation of climate in predictive models, contributing significantly to policy-making. Dr Martí Galí, a researcher at ICM-CSIC, said, “Until now, we believed that oceans only emitted sulfur in the form of dimethyl sulfide, a plankton residue that gives shellfish their distinctive smell.”
Thanks to advanced measurement techniques, the research team was able to quantify the global emission of methanethiol, further enhancing our understanding of clouds over the Southern Ocean and their cooling effect. The team found that methanethiol increases known marine sulfur emissions by an annual global average of 25%.
Dr Julián Villamayor, a co-lead researcher at IQF-CSIC, said, “Although 25% may not seem significant, methanethiol is more efficient at oxidizing and forming aerosols than dimethyl sulfide, thus magnifying its climate impact.”
The study was funded by various organizations, including the European Research Council and Spanish Ministry of Science and Innovation.
