| Recent research identified the presence of nanoparticulate pyrite in hydrothermal vent black smoker emissions, and suggested that these nanoparticles may be a transport pathway for iron from hydrothermal vents to the larger ocean basin. Here, nanoparticulate pyrite was synthesized via a hydrothermal method and oxidized in air- saturated seawater, in order to explore how hydrothermally emitted pyrite forms, and may behave in oxic seawater. Additionally, hydrothermal emissions from the Mid- Atlantic Ridge were investigated for iron and sulfide speciation and reactions relating to pyrite formation.;Pyrite was synthesized via both the Fe(II) + S(0) and the FeS + H 2S pathways of pyrite formation, and factors including surfactant and synthesis time were varied in order to modify morphology. The FeS + H 2S formation pathway, which is likely the pathway of pyrite formation occurring at hydrothermal sites, reproduces the pyrite nano and sub- micron particles found in black smoker emissions most closely. The oxidation of these pyrite particles results in an initial oxidation rate that is first order with respect to both the pyrite and oxygen concentration in seawater. This work is unique to previous studies on pyrite oxidation in that it uses synthesized, rather than ground and sieved pyrite, and uses seawater as the medium of oxidation. Along with the rate data, this study also demonstrates that the initial oxide formed from pyrite oxidation under these conditions is poorly crystalline and contains Fe(II) and Fe(III).;Pyrite nanoparticles were identified at each of the three sites investigated at the Mid-Atlantic Ridge (Rainbow, TAG and Snakepit), and their presence at these sites, when combined with previous data from Lau Basin and EPR 9 °N demonstrates that they are likely to be a ubiquitous component of black- smoker hydrothermal emissions. The Rainbow site exhibited the highest concentration of nanoparticulate pyrite measured anywhere to date (1.15 mM). The potential rates of pyrite formation during hydrothermal buoyant plume rise are investigated, as are the rates of formation for different iron- containing particulates including FeS, silicate formation, and Fe(II) oxidation. |
