Award: OCE-1234827

Intellectual Merit: This project began with the participation of PI Sherrell (Rutgers University) and co-PI C. German (Woods Hole Oceanographic Institution) in a nearly 2 month GEOTRACES research cruise from Peru to Tahiti. The overall goals of the expedition were to measure a large suite of trace elements and isotopes, with supporting hydrographic measurements, along an east-west section of the tropical South Pacific, intersecting the region of high productivity and the sub-surface oxygen minimum zone off Peru and then sampling down the axis of the large hydrothermal plume known to emanate from the East Pacific Rise. Suspended particulate samples were collected at 36 stations during the GEOTRACES EPZT cruise. Samples were collected at each depth sampled (34 depths at the full-depth stations, 12 depths at the short stations) using the GEOTRACES metal-clean CTD/rosette. Seawater was filtered directly from GO-Flo water sampling bottles onto acid-cleaned filters with pore size of 0.45 micrometers. An average of 8.7 liters was filtered through each filter, and in total 924 samples were collected. The Sherrell lab analyzed all intermediate and deepwater samples (depths greater than ~1000m) and the upper water column samples were analyzed by collaborator Dr. Ben Twining (Bigelow Laboratory for Ocean Sciences). Measurements of >40 elements were carried out by acid digestion of the particulate matter, and analysis by Inductively-Coupled Plasma Mass Spectrometry (ICP-MS). The Rutgers and Bigelow labs put great effort into proving excellent intercalibration. In addition to these efforts, samples were collected from a mini-coring device that was deployed on a line hanging from the ship?s CTD and collected ~15-40cm long sediment cores. These included "fluff" layer samples of the unconsolidated sediments sitting just above the sediment-water interface, and samples of the upper 1cm of the consolidated sediments. The goal is to compare the composition of particulate matter comprising the sedimentary record with the composition of suspended particles in the water column, from which they are formed, linking water column processes with the paleoceanographic record of deposition at each station. The most important discovery from this work is that particulate iron and manganese from the oceans? largest known hydrothermal plume travel more than 2500 miles across the deep Pacific. Iron is important in the ocean because levels are generally low and phytoplankton are iron-depleted in more than 25% of the ocean?s surface. Phytoplankton harvest solar power at the base of the marine food chain and help to control carbon dioxide concentrations in the atmosphere. In a report published in Nature Geoscience (Fitzsimmons et al., 2017) the hydrothermal plume is described as residing 1.5 miles down in the Pacific Ocean, and about 600 miles south of the equator. It wafts westward from vents on the East Pacific Rise volcanic mountain ridge, like a giant smoke plume from an industrial smokestack. The plume begins when seawater percolates into the earth?s crust and reacts with hot magma, then spews back out as 700°F hydrothermal fluid in "black smokers" as the concentrated metals dissolved from the rocks are converted to fine particles upon mixing with the cold deep ocean water. While the existence of such vents has been known for 35 years, and metals have been analyzed in seawater samples collected close to the vents, we preciously had no evidence of how far the ?smoke? particles travelled or what effect the plume might have on the overall chemistry of the deep Pacific. Through this study, we know that at least a portion of the particles persist for decades in the slowly moving plume, and can be detected north of Tahiti. Another surprise is that both dissolved and particulate forms of iron descend more than 1000 feet while they are carried west. This indicates that the hydrothermal iron is continuously passed back and forth between the dissolved form and the persistent particles that are sinking at about 2 feet per month, a process that may affect iron distribution throughout the ocean. Broader Impacts: This projected provided an opportunity for training the postdoctoral fellow Dr. Jessica Fitzsimmons who secured a tenure-track position at Texas A&M University upon completion of the project. Fitzsimmons had the opportunity to co-chair the early career workshop immediately prior to the Chemical Oceanography Gordon Research Conference in July 2015 and published the first of a series of papers arising from the project (Nature Geoscience, 2017) Undergraduate intern Alexandra Malinina contributed to processing and analysis of samples, has now completed her BS degree as a Marine Sciences major and is accepted into the Biostatistics graduate program at Rutgers University. A first high impact paper arising from the project, published in Nature Geosciences, generated a special "News & Views" commentary in the journal, and prompted media interest including an article in Fox News online. Last Modified: 06/04/2017 Submitted by: Robert M Sherrell