In late May, a study led by researchers at Oregon State University (OSU) and published in the journal Nature Geosciences suggests that iron released from continental margin sediments could limit the spread and duration of hypoxic areas, also known as dead zones. The iron may act as a natural limiting switch, keeping ocean systems from developing a runaway feedback loop that can result in hypoxic zones. According to researchers, the findings are particularly important as a warmer climate is expected to expand oxygen-minimum zones, affecting coastal fisheries as well as the global carbon cycle.

It is well-documented that iron is a crucial catalyst for fueling biological productivity in the oceans. When there is an insufficient amount of iron in the water column, microscopic plants called phytoplankton cannot fully consume nitrates and phosphates, limiting their growth. There are several potential sources of iron — including river sediments, windblown dust, and continental margin sediments. However, to be useful to plankton, the iron must be dissolved rather than locked up in sediments. Oxygen may be a key that unlocks the storehouse of iron.

“But we found that when the oxygen approaches zero, a new group of minerals — iron sulfides — are formed,” said Florian Scholz, OSU researcher lead author of the study. “This is the key to the limit switch because when the iron gets locked up in sulfides, it is no longer dissolved and thus not available to the plankton. The runaway hypoxia stops and the hypoxic region is limited.”