Research in Lake Superior Reveals How Sulfur Might Have Cycled in Earth’s Ancient Oceans


Geochemist Alexandra Phillips has sulfur on her mind.

Geochemist Alexandra Phillips has sulfur on her mind. The yellow element is a vital macronutrient, and she’s trying to understand how it cycles through the environment. Specifically, she’s curious about the sulfur cycle in Earth’s ancient ocean, some 3 billion years ago.

Fortunately, the nutrient-poor waters of Lake Superior offer a welcome glimpse into the past. “It’s really hard to look back billions of years,” said Phillips, a former postdoctoral researcher at UC Santa Barbara and University of Minnesota, Duluth. “So this is a great window.” She and her co-authors discovered a new type of sulfur cycle in the lake. Their findings, published in Limnology and Oceanography, focus attention on the role organic sulfur compounds play in this biogeochemical cycle.

The sulfate ion (SO4) is the most common form of sulfur in the environment, and a major component of seawater. In the bottoms of oceans and lakes, where oxygen becomes unavailable, some microbes make their living by turning sulfate into hydrogen sulfide (H2S). The fate of this hydrogen sulfide is complex; it can be consumed quickly by microorganisms during respiration, or it can be retained in sediments for millions of years. Converting sulfate into hydrogen sulfide is a time-honored profession; genomic evidence suggests microbes have been doing it for at least 3 billion years.

Read More: University of California - Santa Barbara

The sulfate poor waters of Lake Superior could provide insights on the biochemistry of Earth's early ocean. (Photo Credit: Alexandra Phillips)