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{"Abstract":["This data set presents processed near-bottom data from the Sentry AUV standard sensor package, with corrected NDSF navigation, for Sentry dives S597-S606 at the southern East Pacific Rise. The files contain the NDSF SCC data in Excel spreadsheet format, with one file per dive. The data files were generated as part of the projects called "Are Low-Temperature Hydrothermal Vents an Important but Overlooked Source of Stabilized Dissolved Iron to the Ocean?" and "Finding hydrothermal chimneys along the southern East Pacific Rise with machine learning approaches to AUV-based sonar data". Funding was provided by the U.S. National Science Foundation under awards OCE17-55571, OCE17-56402 and OCE20-06265."]} 

This dataset includes the concentrations of particulate total sulfur, particulate iron, dissolved hydrogen, and dissolved methane measurements for a subset of near-seafloor (< 40 m above bottom) and background water column samples collected on the 18 September to 6 November 2021 PLUME RAIDERS cruise to the 16-18ºS sector of the Southern East Pacific Rise on R/V Roger Revelle. Particulate iron and particulate total sulfur samples were collected at sea and later measured in lab using energy dispersive X-ray fluorescence (ED-XRF). Dissolved hydrogen and methane measurements were collected and processed shipboard using gas chromatography. Dr. Tamara Baumberger and Anson Antriasian generated the dissolved hydrogen and methane data. Nathan Buck generated the particulate iron and particulate total sulfur data."],"Methods":["Samples were collected on the R/V Roger Revelle (cruise RR2106, “PLUME RAIDERS”) expedition to the 16-18ºS section of the southern East Pacific Rise from 18 September to 6 November 2021. Teflon-Lined Go-Flo samplers (General Oceanics) were used to collect water column seawater samples from a trace metal clean CTD-rosette (Seabird Scientific; Cutter and Bruland 2012). Subsamples (100 mL) for dissolved hydrogen and methane were collected via syringe on deck and then analyzed onboard using gas chromatography following the methods outlined in Baumberger et al. (2014) and Kelley et al. (1998). Samples for pFe and pStot were collected in a shipboard clean-air laboratory by filtering seawater (average ~ 6 L) onto 0.2um polycarbonate track etched membrane filters (Whatman) with cellulose ester filter backings (Whatman), followed by a 15 mL rinse step using pH 8 MilliQ-NH4OH solution to remove excess sea salts. Samples were stored in a desiccator until the end of the cruise then later analyzed in the lab using energy dispersion X-ray fluorescence (ED-XRF) following the methods outlined in Buck et al. (2021). References: Baumberger, T., M. D. Lilley, J. A. Resing, J. E. Lupton, E. T. Baker, D. A. Butterfield, E. J. Olson, and G. L. Früh-Green. 2014. Understanding a submarine eruption through time series hydrothermal plume sampling of dissolved and particulate constituents: West Mata, 2008–2012. Geochem. Geophys. Geosystems 15: 4631–4650. doi:10.1002/2014GC005460.Received\n\nBuck, N. J., P. M. Barrett, P. L. Morton, W. M. Landing, and J. A. Resing. 2021. Energy dispersive X-ray fluorescence methodology and analysis of suspended particulate matter in seawater for trace element compositions and an intercomparison with high-resolution inductively coupled plasma-mass spectrometry. Limnol. Oceanogr. Methods 19: 401–415. doi:10.1002/lom3.10433\n\nCutter, G. A., and K. W. Bruland. 2012. Rapid and noncontaminating sampling system for trace elements in global ocean surveys. Limnol. Oceanogr. Methods 10: 425–436. doi:10.4319/lom.2012.10.425\n\nKelley, D. S., M. D. Lilley, J. E. Lupton, and E. J. Olson. 1998. Enriched H2, CH4, 3He concentrations in hydrothermal plumes associated with the 1996 Gorda Ridge eruptive event. Deep-Sea Res. Part II Top. Stud. Oceanogr. 45: 2665–2682. doi:10.1016/S0967-0645(98)00088-5"],"Other":["Funding provided by the National Science Foundation\n\nCrossref Funder Registry ID: https://ror.org/021nxhr62\n\nAward number: 1756402"]} 

Transport processes along the river-ocean continuum influence delivery of nutrients, carbon and trace metals from terrestrial systems to the marine environment, impacting coastal primary productivity and water quality. Although trace metal transformations have been studied extensively in the Mississippi River Delta region of the Northern Gulf of Mexico, investigations of manganese (Mn) and the presence of ligand-stabilized, dissolved manganese (Mn(III)-L) and its role in the transformation of trace elements and organic matter during riverine transport and estuarine mixing have not been considered. This study examined the chemical speciation of dissolved and particulate Mn in the water column and sediment porewaters in the Mississippi River and Northern Gulf of Mexico in March of 2021 to explore transformations in Mn speciation along the river-ocean continuum and the impact of different processes on the distribution of Mn. Total dissolved Mn concentrations were highest in the Mississippi River and decreased offshore, while Mn(III)-L contributed most to the dissolved Mn pool in near-shore waters. Porewater profiles indicated that ligand stabilization prevented dissolved Mn(III) reduction below the depth of oxygen penetration and in the presence of equimolar dissolved iron(II). Dissolved Mn(III)-L was enriched in bottom waters at all Northern Gulf of Mexico stations, and diffusive flux modelling of porewater dissolved Mn suggested that reducing sediments were a source of dissolved Mn to the overlying water column in the form of both reduced Mn(II) and Mn(III)-L. A simple box model of the Mn cycle in the Northern Gulf of Mexico indicates that Mn(III)-L is required to balance the Mn budget in this region and is an integral, and previously unconsidered, piece of the Mn cycle in the Northern Gulf of Mexico. The presence of Mn(III)-L in this system likely has an outsized impact on trace element scavenging rates, oxidative capacity, and the carbon cycle that have not been previously appreciated. 

{"Abstract":["This data set was acquired during cruise RR2106 using 3 separate CTD systems (referred to as "Hydrothermal", "Trace Metal", and "Pump") that all utilized Seabird 911plus CTD systems with various integrated analog sensors (see the associated documentation that identifies the instrument configuration of each system). The data files are in ASCII format and column headers define the fields. Navigation is included in the files. The aim of the study was to evaluate the contribution of low-temperature hydrothermal venting as an important, but overlooked, source of stabilized dissolved iron to the ocean. Operations included near-bottom (20-40 m above the seafloor) CTD tows (using the "Hydrothermal" CTD only) along with vertical casts that were completed using all 3 systems. The CTD data has been processed using Seabird Data Processing modules and averaged to 5-second intervals. Navigation for the tows was calculated using a lay-back method. Primary plume tracers are potential temperature anomaly (ΔTheta, °C), turbidity anomaly (optical backscatter, ΔNTU), and oxidation-reduction potential anomaly (ΔE, mV). Users should refer to the continuous CTD data files (i.e., those with "CTDdata" in the file names) for ΔTheta and ΔE values at the time the bottle samples were obtained; ΔNTU values are included in the "BottleFile" files, which are subsets of the continuous data from the times each bottle sample was obtained (generated by Seabird Data Processing "Bottle Summary" module). The data set was generated as part of the projects called "Are Low-Temperature Hydrothermal Vents an Important but Overlooked Source of Stabilized Dissolved Iron to the Ocean?" and "Low temperature hydrothermal vent fluxes as traced by radium isotopes". Funding was provided by NSF awards OCE17-56402 and OCE18-29431."]} 

This dataset includes the concentrations of total dissolvable iron and manganese, dissolved iron and manganese, and dissolved organic iron-binding ligands collected on the PLUME RAIDERS expedition. Samples were collected during the PLUME RAIDERS cruise (RR2106) on the R/V Roger Revelle from 18 September – 6 November 2021. The main study area was located along the 16-18ºS section of the Southern East Pacific Rise, and the sampling was focused near the ride crest at depths below 1,500 m. Both the total dissolvable and dissolved iron and manganese concentrations were determined shipboard using flow injection analysis. The total organic iron-binding ligand data was generated both shipboard and in the lab using competitive ligand exchange adsorptive cathodic stripping voltammetry. The siderophore concentrations were measured following a solid phase extraction step, and then eluents were measured using inductively coupled plasma mass spectrometry. The dissolvable and dissolved metal data was generated by Dr. Joe Resing and Nathan Buck at NOAA-PMEL and the ligand and siderophore data was generated by Dr. Laura Moore and Dr. Randelle Bundy at the University of Washington. 

Abstract. Supply of iron (Fe) to the surface ocean supports primary productivity, and while hydrothermal input of Fe to the deep ocean is knownto be extensive it remains poorly constrained. Global estimates of hydrothermal Fe supply rely on using dissolved Fe (dFe) toexcess He (xs3He) ratios to upscale fluxes, but observational constraints on dFe/xs3He may be sensitive toassumptions linked to sampling and interpolation. We examined the variability in dFe/xs3He using two methods of estimation, forfour vent sites with different geochemistry along the Mid-Atlantic Ridge. At both Rainbow and TAG, the plume was sampled repeatedly and the range ofdFe/xs3He was 4 to 63 and 4 to 87 nmol:fmol, respectively, primarily due to differences in plume age. To account for backgroundxs3He and shifting plume position, we calibrated He values using contemporaneous dissolved Mn (dMn). Applying thisapproach more widely, we found dFe/xs3He ratios of 12, 4–8, 4–44, and 4–86 nmol fmol−1 for the Menez Gwen, LuckyStrike, Rainbow, and TAG hydrothermal vent sites, respectively. Differences in plume dFe/xs3He across sites were not simplyrelated to the vent endmember Fe and He fluxes. Within 40 km of the vents, the dFe/xs3He ratios decreased to3–38 nmol fmol−1, due to the precipitation and subsequent settling of particulates. The ratio of colloidal Fe to dFe wasconsistently higher (0.67–0.97) than the deep N. Atlantic (0.5) throughout both the TAG and Rainbow plumes, indicative of Fe exchangebetween dissolved and particulate phases. Our comparison of TAG and Rainbow shows there is a limit to the amount of hydrothermal Fe releasedfrom vents that can form colloids in the rising plume. Higher particle loading will enhance the longevity of the Rainbow hydrothermal plume withinthe deep ocean assuming particles undergo continual dissolution/disaggregation. Future studies examining the length of plume pathways required toescape the ridge valley will be important in determining Fe supply from slow spreading mid-ocean ridges to the deep ocean, along with thefrequency of ultramafic sites such as Rainbow. Resolving the ridge valley bathymetry and accounting for variability in vent sources in globalbiogeochemical models will be key to further constraining the hydrothermal Fe flux. 

Eastern Pacific Ocean swath bathymetry was collected with a Simrad EM124 multibeam sonar system on R/V Roger Revelle during PLUME RAIDERS cruise RR2106 in 2021 (investigators Joseph Resing, Scott White, and Chris German). The files were processed in MB-System following standard protocol for navigation, attitude, sound velocity, and bad beams. The data files are in MB-System-compatible format (mbio format 261) and contain processed swath bathymetry and acoustic backscatter data. The files were generated as part of the projects called Finding hydrothermal chimneys along the southern East Pacific Rise with machine learning approaches to AUV-based sonar data; and, Are Low-Temperature Hydrothermal Vents an Important but Overlooked Source of Stabilized Dissolved Iron to the Ocean? Funding was provided through NSF grants OCE20-06265, OCE17-55571, and OCE17-56402. 

Key Points Iron is dispersed from trans Atlantic geotraverse predominantly northward within the axial valley and westward off axis, dominated by the colloidal size fraction A combination of fine‐scale processes are necessary to explain the dispersal both within and outside the axial valley Coarse resolution models are impaired in their ability to constrain the broader influence of iron supplied from axial valley ridge systems