Mercury in Deep Sea Hydrothermal Vent Fluids and Plumes from the Atlantic and Pacific Oceans

The deep sea has been suggested to be an important source of total mercury (Hg) and monomethyl-Hg (HgT and MMHg) to the ocean as a whole, as well as open ocean foodwebs. One pathway by which this might occur is through the venting of hydrothermal fluids into the ocean. We analyzed submarine hydrothermal fluid samples for HgT and MMHg from cruises to the Lau Basin (Sept. 2006), 9°50’N East Pacific Rise (EPR; June 2008) and Rainbow/Lucky Strike on the Mid-Atlantic Ridge (MAR; Jul./Aug. 2008), and compared these results to those from samples collected at Sea Cliff submarine hydrothermal field, Gorda Ridge (Lamborg et al., 2006). The results indicate there is large site-to-site variation, most strikingly in MMHg which was absent from the EPR and MAR sites. Microbial methylation of inorganic mercury in sediments covering the Sea Cliff vent field resulted in nearly complete methylation of inorganic Hg (average 83% MMHg, n=5), while Pacific Deep Water generally has less than 10% MMHg. Filtered and particulate Hg in hydrothermal vent plumes from the MAR and EPR showed changes in speciation within the plumes, however, Hg was only enriched near the MAR.