A model for the production of sulfur floc and “snowblower” events at mid-ocean ridges

At mid-ocean ridges following magmatic eruptions, biogenic floc emerges from the seafloor and blankets regions of the seafloor in what have been called “snowblower” events. The floc often consists of filaments of elemental sulfur, and similar byproducts have been produced by hydrogen sulfide oxidizing bacteria in the laboratory. In this paper we estimate the rate of sulfur floc production in two ways. First, we compare the flux of H₂S from high temperature vents and adjacent diffuse flow near 9°50′N on the East Pacific Rise to estimate the rate at which subsurface microbes use H₂S to produce elemental sulfur in the shallow crust since the 1991 eruption. Second, we use the data from laboratory experiments to provide an upper estimate of sulfur floc production during a volcanic eruption. The results suggest that that the floc observed during “snowblower” events is most likely a combination of a bloom event and floc that has been stored in the crust between eruption cycles. The calculations also suggest that a ∼1% reduction in crustal porosity would result from the microbial production and storage of sulfur floc during the 1991 to 2000 time interval.