Particulate Iron Speciation and Transport in the East Pacific Rise 15oS Hydrothermal “Mega” Plume

Recent geochemical studies have demonstrated multiple mechanisms that allow hydrothermally derived iron to be protected and transported within the buoyant and non-buoyant plume This has become known as the “leaky vent hypothesis” (Toner et al. 2012; Fitzsimmons et al. 2014). The “leaky vent hypothesis” impact on the global iron budget has been difficult to constrain, as mechanisms of hydrothermal iron’s sources and sinks are still poorly understood. Estimates of the hypothesis have either been based on plume or source fluid data alone, which disregards important mechanisms for how iron is protected and transported into, or away from the plume. As part of the US GEOTRACES East Pacific Zonal Transect cruise, marine particles were collect by in-situ filtration over the 4357 km transect of the East Pacific Rise 15^ºS “mega” hydrothermal plume. In addition, samples of seafloor sediment were obtained. In this study, we aim to measure particle chemistry in the EPR 15ºS hydrothermal plume. Our two main goals are to (1) understand how speciation of carbon and sulfur influences the bioavailability and longevity of particulate iron in the marine water column, and (2) investigate the travel distance and redox pathways of particulate iron within the plume. Iron (Fe) and Carbon (C) speciation were measured using the Scanning Transmission X-ray Microscope (STXM, 5.3.2.2) and the X-ray Microprobe (10.3.2) at the Advance Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA and are currently on-going. Sulfur and C were hypothesized to slow the oxidation of Fe(II) based upon similar investigations at EPR 9^ºN. However, while both organic and/or inorganic carbon were present in the samples, sulfur seemed to be depleted and Fe rapidly oxidizes in both the plume and sediments. These findings would suggest sulfur is critical in protecting reduced iron though the hydrothermal plume.