Hydrothermal vents, at the bottom of the ocean, are the link between the earth’s interior and the deep sea.  There are three areas at vents: the hot focused flow commonly seen as black smokers, the plume of particles that arises from these vents and that disperses into the ocean, and lastly the diffuse flow low-temperature areas near hydrothermal vents. The latter supports life via chemosynthesis as the hydrogen sulfide (and other reduced chemical compounds) emanating from the sub-surface is oxidized with bottom water oxygen through bacterial mediation to fix carbon dioxide and produce biomass. The biomass is readily seen as tubeworms, snails, mussels, clams and other organisms. These areas are oases at the bottom of the dark ocean. Image 1 shows that mussels (Bathymodiolus brevior) surround one species of snail (Ifremeria nautilei), which in turn surrounds a second species of snail (Alviniconcha spp.).

In this collaborative study, researchers from the University of Delaware collected temperature and chemical data for 40,000 time points and locations at the Eastern Lau spreading center to understand why snails and mussels reside in apparently separate zones in diffuse flow waters.  The mean and median data (Image 2; note direction of the arrows) indicate that the organisms generally live in an increasing temperature and H₂S regime in the following order: mussels (Bathymodiolus brevior), one species of snail Ifremeria nautilei then a second species of snail Alviniconcha spp.  The average and median O₂ data for these organisms follow an inverse order from the temperature and H₂S. The snail, Alviniconcha spp., has the ability to reside in waters that exhibit very low oxygen conditions (microaerophilic) about half the time based on median O₂ data and the detection limit of the sensor. This ability indicates that these snails can live under what we would call ‘extreme conditions’.

Also, our group has shown that a significantamount of fool’s gold or pyrite is emitted from the hot black smoker hydrothermal vents at the bottom of the ocean as nanoparticles, which have a diameter that is one thousand times smaller than that of a human hair (Image 3 shows a hydrothermal vent with an insert of an electron micrograph showing nanoparticles of pyrite). Fool's gold consists of iron and sulfur as iron disulfide, FeS₂. It is not something miners of the California gold rush in the 1840's wanted when they were looking for gold. However, fool's gold released from hydrothermal vents is as good as gold for bacteria and plankton, which need iron as a micronutrient for growth. 

Although iron is a common element on land, it is present in extremely low dissolved concentrations in the ocean. Because pyrite nanoparticles are so small, they will not settle out and fall to the ocean bottom. Also fool’s gold does not rapidly react with oxygen to form oxidized iron (“rust”) at seawater pH. As pyrite travels from the vents to the ocean interior and toward the surface ocean, it will “time release” iron to areas where iron is depleted so that organisms can assimilate it, then grow. The latter can affect atmospheric oxygen and carbon dioxide levels.  The results indicate that hydrothermal vents are a continuous source of much needed iron in the form of fool’s gold and are an ongoing iron supplement for the ocean much as “Geritol” is for humans.

Also, other research demonstrated how fast all these organisms can take up and use hydrogen sulfide for growth and survival.  The organisms were placed in specially designed high pressure containers and given a ‘diet’ of oxygen, carbon dioxide and hydrogen sulfide as chemical sensors monitored the changes...

Please report errors in award information by writing to: awardsearch@nsf.gov.