Dear faithful readers,

A few posts ago, I promised to write about redox boundaries. Except it dawned on me that I don't really know what they are. I mean, I do, but not well enough to write about them publicly.

Instead, I give you a summary of a lecture I went to that spurred the unkept promise. And perhaps you could explain this redox boundary thing to me.

Bjorn Sundby’s lecture, “What can we learn from metals in the environment: A tale of two oceans” included highlights from research projects involving two bodies of water– the Arctic Ocean and Lake Matano.

In the Artic Ocean, Dr. Sundby’s research team used redox tracers such as manganese, rhenium and AVS (acid-volatile sulfides) to determine the location of the redox boundary in the ocean-floor sediment at several stations in the Arctic Ocean basin. At about 10 cm of depth, ocean-wide, there was an enrichment of AVS, but no
enrichment of rhenium. Organic carbon was found in the top 10 centimeters. Dr. Sundby’s team concluded that recent global warming has reduced the volume of ice in the arctic and caused a huge flux in organic carbon to the ocean floor, which is supported by the position of the redox boundary.

At Lake Matano, the presence of banded iron formations suggests that organisms
inhabiting Earth’s early oceans metabolized Fe2+. Dr. Sundby and his colleagues
studied the chemistry and fauna of the lake and found that at 100m deep, the
environment became anoxic; however, there was photosynthetic activity occurring
below that depth. They determined that between 110 and 120 meters, a mixed community of Chlorobiaceae inhabits the waters. Because the levels of sulfates in the deep waters of Lake Matano are low and the waters are iron-rich, Dr. Sundby’s team concluded that there are ferrophototrophs in the lake and that Lake Matano is a modern analog of the oceans of the Archaean.