Dimethylsulfide (DMS) is a small sulfur-containing organic compound with the formula (CH₃)₂S, and it is best known as the chemical behind the smell of the sea. Produced overwhelmingly by marine phytoplankton, DMS is the most abundant biogenic sulfur gas emitted from the ocean surface, and its roles span from cloud formation in the atmosphere to foraging cues for seabirds to flavor chemistry in beer and wine. It also shows up in unexpected places: the breath of people with liver disease, the soils of peatlands, and even the list of potential biosignatures on distant exoplanets.
Where DMS Comes From
The vast majority of DMS originates in the ocean. Marine phytoplankton, especially certain species of algae, produce a precursor molecule called dimethylsulfoniopropionate, or DMSP. When DMSP breaks down, one of the products is DMS. For a long time, the specific enzyme responsible for this conversion inside the algae themselves was unknown, but researchers identified it in 2015 in the bloom-forming alga Emiliania huxleyi, naming the enzyme Alma1.1PubMed. Identification of the algal dimethyl sulfide-releasing enzyme: A missing link in the marine sulfur cycle That discovery filled in a long-standing gap in our understanding of how sulfur moves through the marine food web and ultimately into the atmosphere.
Algae are not the only organisms that convert DMSP into DMS. Bacteria in seawater carry a suite of genes that cleave DMSP and release DMS as a byproduct.2PubMed. Genomic insights into bacterial DMSP transformations Bacterial catabolism of DMSP is actually the dominant conversion route in the ocean, but DMS is not the only fate of that sulfur. Bacteria can also shunt DMSP into other chemical pathways that keep the sulfur dissolved in seawater rather than releasing it as a gas.3PubMed Central. Bacterial Catabolism of Dimethylsulfoniopropionate (DMSP) – Section: Abstract The balance between DMS release and these alternative pathways determines how much sulfur actually escapes the ocean surface and enters the atmosphere.
How DMS Concentrations Vary Across the Ocean
DMS is not spread evenly through the world’s oceans. Concentrations follow strong seasonal and geographic patterns, peaking in summer when phytoplankton blooms are most active. In the Northern Hemisphere, the highest concentrations appear in the North Pacific between about 40°N and 60°N, where summer values can exceed 10 nanomoles per liter, and in the subarctic North Atlantic. In the Southern Hemisphere, a ring-shaped band of elevated DMS sits near 40°S along the Subtropical Convergence, and Antarctic coastal waters also show high summer peaks above 4 nanomoles per liter.4Earth System Science Data. A 20-year (1998–2017) global sea surface dimethyl sulfide gridded dataset with daily resolution Between these hotspots, large stretches of open ocean show much lower concentrations year-round.
Those atmospheric concentrations vary accordingly. Measurements of DMS in the air over equatorial waters have averaged around 30 nanograms per cubic meter, while polar regions near the Falkland Islands have recorded concentrations an order of magnitude higher, sometimes exceeding 1,000 nanograms per cubic meter. The difference reflects both the intensity of phytoplankton activity at high latitudes and the relatively clean atmospheric background that allows DMS to accumulate without being diluted by other pollutants.
Climate change is expected to reshape this distribution. Modeling work suggests that globally averaged seawater DMS concentrations will decrease under warming scenarios, but not uniformly. The northern polar region is projected to see increases of roughly 6 to 8 percent depending on the warming scenario, while the southern polar region could see decreases of anywhere from about 7 to nearly 18 percent.5PubMed Central. Climate warming increases global oceanic dimethyl sulfide emissions The Arctic increase likely reflects ice retreat opening new water to phytoplankton blooms, while warming and stratification in the Southern Ocean may suppress productivity. These shifts matter because of what DMS does once it leaves the water.
The Cloud Connection
Once DMS escapes the ocean surface, it reacts with hydroxyl radicals and other oxidants in the atmosphere. The main products of this oxidation are sulfuric acid and methanesulfonic acid, both of which can form tiny particles that serve as cloud condensation nuclei. In the 1980s, a landmark hypothesis proposed that this process created a climate feedback loop: warmer temperatures would boost phytoplankton growth, increase DMS emissions, seed more clouds, reflect more sunlight, and cool the planet back down. The idea became known as the CLAW hypothesis, after the initials of its four authors.
Field studies have confirmed individual links in that chain. A study in the Arctic directly tracked the sequence from DMS emissions through new particle formation to the growth of particles into sizes that can seed clouds, demonstrating that DMS-derived aerosol can produce climate-relevant cloud condensation nuclei in real atmospheric conditions.6Global Biogeochemical Cycles. Dimethyl Sulfide‐Induced Increase in Cloud Condensation Nuclei in the Arctic Atmosphere And experiments at the CLOUD chamber at CERN have shown that at low temperatures, methanesulfonic acid production from DMS oxidation jumps by roughly a factor of ten compared to warm conditions, making DMS a more potent source of cloud-seeding particles in polar regions than earlier models predicted.7Environmental Science & Technology. High Gas-Phase Methanesulfonic Acid Production in the OH-Initiated Oxidation of Dimethyl Sulfide at Low Temperatures
However, the full CLAW feedback loop as originally proposed has not held up. The sensitivity of cloud condensation nuclei to changes in DMS flux turns out to be very low: modeling estimates suggest that a 1 percent change in DMS produces only about a 0.02 percent change in cloud nuclei concentrations in the Northern Hemisphere and roughly 0.07 percent in the Southern Hemisphere.8Atmospheric Chemistry and Physics. Low sensitivity of cloud condensation nuclei to changes in the sea-air flux of dimethyl-sulphide A prominent 2011 review in Nature concluded that the biological control of cloud nuclei via DMS probably does not exist as a coherent feedback mechanism, and that the relationship between ocean biology, aerosol, and clouds is far more complex than the elegant loop originally envisioned.9PubMed. The case against climate regulation via oceanic phytoplankton sulphur emissions DMS does contribute meaningfully to marine aerosol, especially in pristine ocean regions far from anthropogenic pollution. But calling it a planetary thermostat overstates the evidence.
DMS as an Ecological Signal
If you are a seabird hunting over thousands of kilometers of open ocean, you need some way to find prey. Several groups of tube-nosed seabirds, known as procellariiforms, have turned out to be remarkably adept at detecting DMS, using it as an olfactory road map. When phytoplankton are grazed by krill and other zooplankton, DMSP in the algal cells gets broken down and releases a burst of DMS. The gas becomes a chemical signal marking active grazing zones, exactly the places where a seabird would want to hunt.
Controlled experiments at sea near South Georgia Island demonstrated that procellariiform seabirds respond to DMS plumes, with some species such as storm petrels being strongly attracted to it.10PubMed Central. Sensitivity to dimethyl sulphide suggests a mechanism for olfactory navigation by seabirds – Section: Abstract Further work showed that DMS concentrations tend to be higher over predictable ocean features like seamounts and upwelling zones, suggesting that seabirds may use DMS not just to find individual prey patches but to navigate toward productive ocean regions across vast distances.11PubMed. Olfactory foraging by Antarctic procellariiform seabirds: life at high Reynolds numbers
The story goes deeper than a simple predator-prey cue. Researchers have presented evidence that this DMS-mediated interaction functions as a three-way mutualism. Seabirds that follow DMS plumes preferentially consume the zooplankton grazing on phytoplankton, reducing grazing pressure. Their iron-rich excrement then fertilizes the water and stimulates further phytoplankton growth. The phytoplankton produce more DMSP, which produces more DMS, which attracts more seabirds. It is a chemically mediated cycle linking primary producers at the bottom of the food web to top predators at the top.
An Antioxidant for Corals
Corals are among the most prolific producers of DMSP in the ocean, yet for a long time, researchers were not sure why. Increasing evidence points to DMSP and its breakdown products, including DMS, functioning as an antioxidant system within the coral holobiont, the combined organism of coral animal and its symbiotic algae. When corals experience stress from high water temperatures, intense light, low salinity, or exposure to air at low tide, their symbiotic algae can produce harmful reactive oxygen species that threaten cell integrity.12Biogeosciences. Dimethylsulfide (DMS), marine biogenic aerosols and the ecophysiology of coral reefs – Section: The coral antioxidant response
DMSP, DMS, and a related compound called acrylate can all scavenge these reactive oxygen species, helping to keep oxidative damage below the coral’s tolerance threshold. Studies on multiple coral species have found that stressed corals ramp up DMSP production, and that concentrations of its oxidation product DMSO correlate positively with overall antioxidant capacity.13Limnology and Oceanography. Effects of environmental factors on dimethylated sulfur compounds and their potential role in the antioxidant system of the coral holobiont – Section: Abstract This finding has implications for understanding coral bleaching: the DMSP-DMS system may represent one of the biochemical defenses that buys corals time under stress before their symbiotic relationship breaks down.14PubMed Central. Dimethylsulfoniopropionate, superoxide dismutase and glutathione as stress response indicators in three corals under short-term hyposalinity stress – Section: Abstract
DMS in Food, Beer, and Wine
If you have ever noticed a faintly cabbage-like or “cooked corn” note in a lager, you have encountered DMS in your glass. Brewers pay close attention to DMS because its precursor, S-methylmethionine, forms naturally during the malting of barley. During the boil, DMS is driven off as steam, but if wort is cooled too slowly or if fermentation does not scrub enough of it out, DMS can persist above its flavor threshold and produce that characteristic off-note. Ale fermentations tend to remove DMS more effectively because of their warmer, more vigorous activity, which is one reason lagers are historically more susceptible to the problem.
In wine, DMS plays a more ambiguous role. At low concentrations, it can contribute positive fruity or truffle-like aromas, particularly in aged red wines. Under oxidative aging conditions, however, DMS tends to disappear quickly. One study found that DMS and related sulfides vanished after just 15 days of oxidative aging in a botrytized red wine.15PubMed. Model aging and oxidation effects on varietal, fermentative, and sulfur compounds in a dry botrytized red wine This makes DMS a fleeting character in wines exposed to oxygen, but a persistent one in reductive (low-oxygen) aging environments, where it can accumulate and shift the aroma profile over years of cellaring.
DMS also turns up in cooked seafood. Analytical work on the odor-active compounds in cooked Chinese mitten crab identified DMS as one of the key volatile contributors to the meat’s characteristic aroma.16Journal of Food and Drug Analysis. Determination of odour-active compounds in the cooked meat of Chinese mitten crab (Eriocheir Sinensis) That distinctive “ocean” smell in cooked shellfish is, in part, DMS doing what it does everywhere else: being volatile and pungent at remarkably low concentrations.
Industrial and Chemical Uses
Outside the natural world, DMS has a handful of industrial applications. Its most significant use is as a feedstock for the production of dimethyl sulfoxide, or DMSO, one of the most widely used solvents in chemistry and pharmaceuticals. DMSO dissolves an unusually broad range of both polar and nonpolar substances, which makes it valuable in drug formulation, electronics manufacturing, pesticide production, and defense-related chemistry. The industrial synthesis of DMSO typically involves oxidizing DMS, using methanol and hydrogen sulfide as upstream starting materials.17Resources Chemicals and Materials. Process simulation and optimization for an efficient synthesis of Dimethyl Sulfoxide – Section: Abstract
DMS also finds use as a sulfiding agent in petroleum refining. Hydrotreating catalysts that remove sulfur from crude oil fractions need to be activated by exposure to a sulfur compound, and DMS is one of the agents used for that purpose. Additionally, organosulfur compounds including DMS and its relatives are intentionally added to natural gas as odorants. Natural gas is odorless in its pure state, so utilities add tiny amounts of sulfur-containing chemicals to give it a detectable smell, providing a safety warning in case of leaks.
DMS and Human Health
Your body produces small amounts of DMS as a normal byproduct of methionine metabolism, and under healthy conditions it is present at low levels in breath and blood. But in certain disease states, DMS levels rise dramatically enough to become clinically noticeable. The distinctive breath odor associated with advanced liver disease, known as fetor hepaticus, is primarily caused by elevated DMS in exhaled air. A study using gas chromatography to analyze breath in liver patients found that DMS was the main compound responsible for the characteristic smell, and that breath DMS levels could discriminate between liver patients and healthy controls with high accuracy.18PubMed. GC-MS analysis of breath odor compounds in liver patients – Section: RESULTS
DMS has also been identified as the primary cause of a specific type of halitosis that does not originate in the mouth. Most bad breath comes from bacterial activity on the tongue and gums and is carried by hydrogen sulfide and methyl mercaptan. But in rare cases, patients have persistent halitosis that is present in both mouth and nose breath, which points to a blood-borne source rather than an oral one. Researchers found that in all such cases they studied, elevated DMS in the bloodstream was the culprit, likely due to a previously unrecognized metabolic disorder.19PubMed. Intra- and extra-oral halitosis: finding of a new form of extra-oral blood-borne halitosis caused by dimethyl sulphide – Section: RESULT This distinction matters clinically, because standard oral hygiene treatments do nothing for blood-borne DMS. Patients with this form of halitosis need to be evaluated for underlying metabolic or hepatic issues rather than sent back to the dentist.
Terrestrial Sources and Peatlands
Although the ocean dominates global DMS production, the gas also escapes from land-based environments, particularly wetlands and peatlands. A study of DMS emissions from a slightly acidic peatland found that the gas was being produced primarily through the degradation of organic matter rather than through sulfate reduction, which had been the assumed pathway.20Journal of Geophysical Research: Biogeosciences. Dimethyl Sulfide Emissions From a Peatland Result More From Organic Matter Degradation Than Sulfate Reduction – Section: Abstract This is a meaningful distinction because the two pathways respond differently to environmental changes. If organic matter decomposition is the dominant driver, then factors like temperature, moisture, and the quality of plant litter will control DMS emissions from these ecosystems, and projections based solely on sulfate availability would underestimate them.
Terrestrial DMS emissions are tiny compared to oceanic ones in the global budget, but they can be locally significant. Salt marshes, agricultural soils amended with sulfur-containing fertilizers, and even certain crops like brassicas (cabbage, broccoli, kale) release DMS during decomposition. For people living near these sources, the characteristic smell can be a genuine nuisance, even though the concentrations involved are far below any health concern.
DMS as a Possible Biosignature on Other Worlds
The association between DMS and biological activity has given it a second career in astrobiology. On Earth, DMS is produced almost exclusively by living organisms, which makes it a compelling candidate as a biosignature gas: a molecule whose detection in the atmosphere of another planet would suggest life. The James Webb Space Telescope (JWST) has brought this from theory into practice. Transit spectroscopy observations of exoplanets have already flagged DMS as a compound of interest, with tentative detections raising the question of whether biological processes could be at work.21Highlights in Science, Engineering and Technology. Optimization Pathways for Exoplanet Atmospheric Spectroscopy Detection – Section: Abstract
The challenge is that detecting a trace gas at interstellar distances is extraordinarily difficult, and DMS’s spectral features overlap with those of other molecules. A positive detection would not be proof of life on its own; it would need to be interpreted alongside the planet’s other atmospheric chemistry, temperature, and stellar environment. Still, DMS sits on a short list of molecules that astrobiologists consider worth searching for specifically because no significant abiotic source for it has been identified. If a rocky planet in the habitable zone of a nearby star showed DMS in its atmosphere at concentrations that could not be explained by photochemistry or volcanism, it would be among the strongest circumstantial cases for extraterrestrial biology that current technology could produce.