The “smell of the sea” is the signature of a sulfur compound called Dimethyl Sulfide (DMS). This gas is produced in vast quantities across the world’s oceans and released from the surface into the atmosphere. DMS is a molecule that connects the planet’s biological systems with its atmospheric ones. Its production makes it a major player in the global sulfur cycle, linking microscopic life to large-scale planetary processes.
The Biological Origins of DMS
Dimethyl Sulfide originates from microscopic life in the ocean, specifically phytoplankton. These tiny marine algae produce a chemical called dimethylsulfoniopropionate (DMSP) to protect themselves from the high-salt environment and other stressors. DMSP helps the algae maintain a proper water balance within their cells. The production of DMS itself does not happen directly within living phytoplankton.
The release of DMS gas is a result of the marine food web. When phytoplankton die or are consumed by organisms like zooplankton, the DMSP stored in their cells is released into the water. Marine bacteria then break down this released DMSP through enzymatic processes, with one of the byproducts being DMS gas. This process creates a constant flux of DMS from the ocean’s surface into the atmosphere.
DMS and Cloud Formation
Once DMS enters the atmosphere, it begins a chemical journey linked to cloud formation. The gaseous DMS reacts with other molecules in the air through oxidation, transforming it into tiny solid particles called sulfate aerosols. These microscopic particles are necessary for cloud development because they act as cloud condensation nuclei (CCN), or “cloud seeds.”
For clouds to form, water vapor in the atmosphere needs a surface upon which to condense into liquid droplets. Over the open ocean, where particles like dust are scarce, sulfate aerosols derived from DMS provide these necessary surfaces. Water vapor molecules collect on these DMS-derived seeds, growing into the tiny droplets that collectively form a visible cloud.
The Climate Feedback Loop
The clouds generated by DMS are bright and dense, making them effective at reflecting sunlight back into space. This reflection has a cooling effect on the Earth’s surface. This observation is the basis of a proposed climate-regulating mechanism known as the CLAW hypothesis.
The proposed cycle begins with ocean temperatures. An increase in sea surface temperature could lead to more favorable conditions for phytoplankton growth. A larger phytoplankton population would, in turn, release more DMS into the atmosphere. This increased DMS would then generate more sulfate aerosols, leading to the formation of more and brighter clouds, which reflect more sunlight and help to cool the ocean surface, completing the feedback loop.