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https://erddap.bco-dmo.org/erddap/tabledap/bcodmo_dataset_925569_v1 https://erddap.bco-dmo.org/erddap/tabledap/bcodmo_dataset_925569_v1.graph https://erddap.bco-dmo.org/erddap/files/bcodmo_dataset_925569_v1/ public [Cr concentration and isotope data using dissolved Cr and different Cr species from RR1805] - Chromium (Cr) concentration and isotope data determined using dissolved Cr and different Cr species from samples collected on R/V Roger Revelle cruise RR1805 in April-May 2018 (Cr Isotope Oceanography of the Eastern Tropical North Pacific Ocean) Changes in chromium (Cr) isotope ratios due to fractionation between trivalent (Cr(III)) and hexavalent (Cr(VI)) are being utilized by geologists to infer oxygen conditions in past environments. But there is little information available on Cr in the modern ocean to ground-truth these inferences. Transformations between the two chromium redox species are important processes in oceanic Cr cycling. Here we present profiles of hexavalent and trivalent Cr concentrations and stable isotope ratios from the Eastern Tropical North Pacific (ETNP) oxygen deficient zone (ODZ) which support theoretical and experimental studies that predict that lighter Cr is preferentially reduced in low oxygen environments, and that residual dissolved Cr becomes heavier due to removal of particle-reactive Cr(III) on sinking particles. The Cr(III) maximum dominantly occurs in the upper portion of the ODZ, implying that microbial activity (dependent on the sinking flux of organic matter) may be the dominant mechanism for this transformation, rather than a simple inorganic chemical conversion between the species depending on the redox potential.\n\ncdm_data_type = Other\nVARIABLES:\nCruise (unitless)\nStation (unitless)\nLatitude (degrees_north)\nlongitude (degrees_east)\ndepth (m)\nTotal_dissolved_Cr (nanomoles per kilogram (nmol/kg))\nTotal_dissolved_d53Cr (permil (‰))\nCrIII (nanomoles per kilogram (nmol/kg))\nd53CrIII (permil (‰))\nCrIII_pcnt_of_total (percent (%))\nCalculated_CrVI (nanomoles per kilogram (nmol/kg))\nCalculated_d53CrVI (permil (‰))\nMeasured_CrVI (nanomoles per kilogram (nmol/kg))\nMeasured_d53Cr (permil (‰))\n https://erddap.bco-dmo.org/erddap/info/bcodmo_dataset_925569_v1/index.htmlTable https://www.bco-dmo.org/dataset/925569 (external link) https://erddap.bco-dmo.org/erddap/rss/bcodmo_dataset_925569_v1.rss https://erddap.bco-dmo.org/erddap/subscriptions/add.html?datasetID=bcodmo_dataset_925569_v1&showErrors=false&email= BCO-DMO bcodmo_dataset_925569_v1
https://erddap.bco-dmo.org/erddap/tabledap/bcodmo_dataset_925726_v1 https://erddap.bco-dmo.org/erddap/tabledap/bcodmo_dataset_925726_v1.graph https://erddap.bco-dmo.org/erddap/files/bcodmo_dataset_925726_v1/ public [Total dissolved Cr concentration and isotopic composition in the ETNP from RR1804-05 and KM1919-20] - Total dissolved chromium (Cr) concentration and isotopic composition in the Eastern Tropical North Pacific from samples collected on R/V Roger Revelle and R/V Kilo Moana in April-May 2018 and Sept-Oct 2019 (Cr Isotope Oceanography of the Eastern Tropical North Pacific Ocean) Understanding the cycling of chromium (Cr) and how chromium stable isotopes (δ53Cr) are altered in response to different processes in the modern ocean is important in our interpretation of marine sedimentary δ53Cr records, a promising redox proxy. Therefore, it is crucial to investigate the geochemical processes of Cr in reducing environments such as oxygen deficient zones (ODZs). In this study, we investigated the cycling of Cr in the Eastern Tropical North Pacific (ETNP) ODZ by analyzing the [Cr] and δ53Cr of total dissolved Cr and Cr(III). Our Cr(III) data at two inshore stations shows profile features and Cr reduction isotopic fractionation factor (-1.5‰) similar to an offshore station in a previous study. We also observed significant Cr scavenging signals in the upper 1000 meters (m) throughout the ODZ with an inshore-offshore variability in its magnitude. Specifically, anoxic bottom waters on the continental slope see the greatest Cr scavenging with heaviest δ53Cr (+1.85‰). Our estimates of the scavenged Cr isotopic composition are within error of the anoxic and euxinic marine sedimentary δ53Cr. This implies that the vertical transport of Cr to the seafloor and subsequent diagenesis may not generate significant isotopic fractionation for Cr. This is the first thorough investigation into the Cr cycling in the ETNP ODZ and demonstrated promising usage of marine sedimentary δ53Cr as a redox proxy for ancient oceans.\n\nIn the ODZ, oxygen is consumed by degrading sinking particles and reaches extremely low levels (too low to support aerobic life) from 100m to 800m depth. However, microbes that can use other oxidants such as nitrate to metabolize organic carbon live there, and we showed that they also convert soluble anionic chromate Cr(VI) to cationic Cr(III), about half of which is scavenged onto sinking particles and removed to the seafloor. This reduction is accompanied by preferential reduction of light Cr isotopes, so the Cr(III) is 1.3‰ lighter than the source Cr(VI). The removal of part of this light Cr(III) by scavenging leaves the residual total Cr heavier than the source Cr. The analyzed samples listed here were chosen to be from the center and margins of the ETNP ODZ and over extremely reducing continental margin sediments.\n\ncdm_data_type = Other\nVARIABLES:\nCruise (unitless)\nStation (unitless)\nLatitude (degrees_north)\n... (5 more variables)\n https://erddap.bco-dmo.org/erddap/info/bcodmo_dataset_925726_v1/index.htmlTable https://www.bco-dmo.org/dataset/925726 (external link) https://erddap.bco-dmo.org/erddap/rss/bcodmo_dataset_925726_v1.rss https://erddap.bco-dmo.org/erddap/subscriptions/add.html?datasetID=bcodmo_dataset_925726_v1&showErrors=false&email= BCO-DMO bcodmo_dataset_925726_v1

 
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