The secrets of the sulfur cycle
There’s still a lot we don’t know about the biogeochemical cycling of sulfur, and this could impact our ability to correctly model the climate. Rachel Brazil talks to the researchers trying to fill in the gaps.
It’s the fifth most abundant element in the universe, the 15th most abundant in the earth’s crust and it’s essential for life, but sulfur seems to be the element that people forget about. As with carbon, nitrogen and phosphorus, its use and chemical conversion through the physical and biological world is described in a cycle. But some of that cycle is not well understood, particularly how small organo-sulfur molecules are produced and used in the oceans.
The biogeochemical sulfur cycle describes how sulfur in different chemical states moves between living systems, the ocean, land and the atmosphere; the ocean is a major sulfur reservoir, containing large quantities of dissolved sulfate wash-out from gypsum and other minerals. Bacterial species can reduce these to sulfides which are incorporated into organic compounds. Small sulfur-containing molecules eventually released into the ocean return to the atmosphere as DMS, which is then oxidised and recycled via rainwater. It is the biological part of the sulfur cycle where there is still so much to learn.