Description: The Peruvian upwelling zone is one of the most productive marine ecosystems in the world with a spectacular, pronounced oxygen minimum zone (OMZ). Globally OMZs are increasing in size and intensity with far-reaching consequences for the marine biological carbon pump and carbon export; thus, these zones need to be carefully monitored to be able to understand future climate change impacts. The current study was carried out in 2013 and 2017 to quantify the vertical flux of organic matter exported out of the productive surface layer by measuring 234Thsingle bond238U disequilibria in the water column. Samples were collected in January 2013 and May 2017 along an identical transect located at 12°S off the Peruvian coast near Lima, Peru. Th-234 fluxes ranged from 0 to 2088 ± 95 dpm m−2 d−1 in 2013 and 698 ± 63 to 3648 ± 113 dpm m−2 d−1 in 2017. The corresponding POC fluxes varied between 0 and 164.2 ± 7.9 mg C m−2 d−1 in 2013 and 22.7 ± 2.7 to 133.1 ± 15.2 mg C m−2 d−1 in 2017, with POC fluxes gradually decreasing with distance from the coast. Despite higher POC fluxes, the export efficiencies were found to be extremely low due to high particle remineralization rates observed within the euphotic zone.

Description: Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 56 (2009): 875-891, doi:10.1016/j.dsr.2009.01.008.

Description: Direct measurements of new production and carbon export in the subtropical North Atlantic Ocean appear to be too low when compared to geochemical based estimates. It has been hypothesized that episodic inputs of new nutrients into surface water via the passage of mesoscale eddies or winter storms may resolve at least some of this discrepancy. Here, we investigated particulate organic carbon (POC), particulate organic nitrogen (PON), and biogenic silica (BSiO2) export using a combination of water column 234Th:238U disequilibria and free-floating sediment traps during and immediately following two weather systems encountered in February and March 2004. While these storms resulted in a 2-4 fold increase in mixed layer NO3 inventories, total chlorophyll a and an increase in diatom biomass, the systems was dominated by generally low 234Th:238U disequilibria, suggesting limited particle export. Several 234Th models were tested, with only those including non-steady state and vertical upwelling processes able to describe the observed 234Th activities. Although upwelling velocities were not measured directly in this study, the 234Th model suggests reasonable rates of 2.2 to 3.7 m d-1. Given the uncertainties associated with 234Th derived particle export rates and sediment traps, both were used to provide a range in sinking particle fluxes from the upper ocean during the study. 234Th particle fluxes were determined applying the more commonly used steady state, 1-dimensional model with element/234Th ratios measured in sediment traps. Export fluxes at 200 m ranged from 1.91 ± 0.20 to 4.92 ± 1.22 mmol C m-2 d-1, 0.25 ± 0.08 to 0.54 ± 0.09 mmol N m-2 d-1, and 0.22 ± 0.04 to 0.50 ± 0.06 mmol Si m-2 d-1. POC export efficiencies (Primary Production/Export) were not significantly different from the annual average or from time periods without storms, although absolute POC fluxes were elevated by 1-11%. This increase was not sufficient, however, to resolve the discrepancy between our observations and geochemical based estimates of particle export. Comparison of PON export rates with simultaneous measurements of NO3 - uptake derived new production rates, suggested that only a fraction, 〈 35%, of new production was exported as particles to deep waters during these events. Measured bSiO2 export rates were more than a factor of two higher (p 〈 0.01) than the annual average, with storm events contributing as much as 50% of annual bSiO2 export in the Sargasso Sea. Furthermore it appears that 65 - 95% (average 86 ± 14%) of the total POC export measured in this study was due to diatoms. Combined these results suggest that winter storms do not significantly increase POC and PON export to depth. Rather, these storms may play a role in the export of bSiO2 to deep waters. Given the slower remineralization rates of bSiO2 relative to POC and PON, this transport may, over time, slowly decrease water column silicate inventories, and further drive the Sargasso Sea towards increasing silica limitation. These storm events may further affect the quality of the POC and PON exported given the large association of this material with diatoms during these periods.

Description: This study was funded by the National Science Foundation (Chemical Oceanography Grants OCE-0244612 and OCE-0241645).

Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 40 (2013): 1557–1561, doi:10.1002/grl.50219.

Description: In the past two decades, a number of studies have been carried out in the Southern Ocean to look at export production using drifting sediment traps and thorium-234 based measurements, which allows us to reexamine the validity of using the existing relationships between production, export efficiency, and temperature to derive satellite-based carbon export estimates in this region. Comparisons of in situ export rates with modeled rates indicate a two to fourfold overestimation of export production by existing models. Comprehensive analysis of in situ data indicates two major reasons for this difference: (i) in situ data indicate a trend of decreasing export efficiency with increasing production which is contrary to existing export models and (ii) the export efficiencies appear to be less sensitive to temperature in this region compared to the global estimates used in the existing models. The most important implication of these observations is that the simplest models of export, which predict increase in carbon flux with increasing surface productivity, may require additional parameters, different weighing of existing parameters, or separate algorithms for different oceanic regimes.

Description: This work was supported by NASA award number NNX08AB48G.

Description: 2013-10-23

Description: Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 55 (2008): 1473-1490, doi:10.1016/j.dsr2.2008.02.010.

Description: The vertical distributions of cobalt, iron, and manganese in the water column were studied during the E-Flux Program (E-Flux II and III), which focused on the biogeochemistry of cold-core cyclonic eddies that form in the lee of the Hawaiian Islands. During E-Flux II (January 2005) and E-Flux III (March 2005), 17 stations were sampled for cobalt (n =147), all of which demonstrated nutrient-like depletion in surface waters. During E-Flux III, two depth profiles collected from within a mesoscale coldcore eddy, Cyclone Opal, revealed small distinct maxima in cobalt at ~100m depth and a larger inventory of cobalt within the eddy. We hypothesize that this was due to a cobalt concentrating effect within the eddy, where upwelled cobalt was subsequently associated with sinking particulate organic carbon (POC) via biological activity and was released at a depth coincident with nearly complete POC remineralization (Benitez-Nelson et al. 2007). There is also evidence for the formation of a correlation between cobalt and soluble reactive phosphorus during E-Flux III relative to the E-Flux II cruise that we suggest is due to increased productivity, implying a minimum threshold of primary production below which cobalt-phosphate coupling does not occur. Dissolved iron was measured in E-Flux II and found in somewhat elevated concentrations (~0.5nM) in surface waters relative to the iron depleted waters of the surrounding Pacific (Fitzwater et al. 1996), possibly due to island effects associated with the iron-rich volcanic soil from the Hawaiian Islands and/or anthropogenic inputs. Distinct depth maxima in total dissolved cobalt were observed at 400 to 600m depth, suggestive of the release of metals from the shelf area of comparable depth that surrounds these islands.

Description: This research was supported by NSF Grants OCE-0327225, OCE-0452883, OPP-0440840, the Office of Naval Research, the Center for Environmental Bioinorganic Chemistry at Princeton, and the Center for Microbial Oceanography and Education.

Description: Intercomparision of 234Th measurements in both water and particulate samples was carried out between 15 laboratories worldwide, as a part of GEOTRACES inter-calibration program. Particulate samples from four different stations namely BATS (both shallow and deep) and shelf station (shallow) in Atlantic and SAFE (both shallow and deep) and Santa Barbara station (shallow) in Pacific were used in the effort. Particulate inter-calibration results indicate good agreement between all the participating labs with data from all labs falling within the 95% confidence interval around the mean for most instances. Filter type experiments indicate no significant differences in 234Th activities between filter types and pore sizes (0.2–0.8 μm). The only exception are the quartz filters which are associated with 10-20% higher 234Th activities attributed to sorption of dissolved 234Th. Flow rate experiments showed a trend of decreasing 234Th activities with increasing flow rates (2-9 L min-1) for 〉51μm size particles, indicating particle loss during the pumping process. No change in 234Th activities on small particles was observed with increasing flow-rates. 234Th inter-calibration results from deep water samples at SAFe station indicate a variability of 〈3% amongst labs while dissolved 234Th data from surface water at Santa Barbara Station show a less robust agreement, possibly due to the loss of 234Th from decay and large in-growth corrections as a result of long gap between sample collection and processing.

Description: Author Posting. © Association for the Sciences of Limnology and Oceanography, 2012. This article is posted here by permission of Association for the Sciences of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography: Methods 10 (2012): 631-644, doi:10.4319/lom.2012.10.631.

Description: Intercomparision of 234Th measurements in both water and particulate samples was carried out between 15 laboratories worldwide, as a part of GEOTRACES inter-calibration program. Particulate samples from four different stations namely BATS (both shallow and deep) and shelf station (shallow) in Atlantic and SAFE (both shallow and deep) and Santa Barbara station (shallow) in Pacific were used in the effort. Particulate intercalibration results indicate good agreement between all the participating labs with data from all labs falling within the 95% confidence interval around the mean for most instances. Filter type experiments indicate no significant differences in 234Th activities between filter types and pore sizes (0.2-0.8 μm). The only exception are the quartz filters, which are associated with 10% to 20% higher 234Th activities attributed to sorption of dissolved 234Th. Flow rate experiments showed a trend of decreasing 234Th activities with increasing flow rates (2-9 L min-1) for 〉 51 μm size particles, indicating particle loss during the pumping process. No change in 234Th activities on small particles was observed with increasing flow-rates. 234Th intercalibration results from deep water samples at SAFe station indicate a variability of 〈 3% amongst labs while dissolved 234Th data from surface water at Santa Barbara Station show a less robust agreement, possibly due to the loss of 234Th from decay and large in-growth corrections as a result of long gap between sample collection and processing.

Description: This research is funded by NSF Chemical Oceanography program. LM will like to thank Fisheries and Oceans Canada for support. PM is supported through ICREA Academia funded by Generalitat de Catalunya. The International Atomic Energy Agency is grateful to the Government of the Principality of Monaco for the support provided to its Environment Laboratories.

Description: Dataset: Organic polymers and domoic acid

Description: Organic polymer formation and domoic acid adsorption. Results from lab experiments designed to investigate organic polymer formation and domoic acid adsorption. Water samples were collected in the northern Gulf of Mexico in 2018 and 2019. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/808280

Description: NSF Division of Ocean Sciences (NSF OCE) OCE-1558957, U.S. Food and Drug Administration (FDA) 5U19FD005923-04

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 126(5), (2021): e2020JG006217, https://doi.org/10.1029/2020JG006217.

Description: It is assumed that to treat excess NO3− high soil organic matter content (%OM) is required to maintain high denitrification rates in natural or restored wetlands. However, this excess also represents a risk by increasing soil decomposition rates triggering peat collapse and wetland fragmentation. Here, we evaluated the role of %OM and temperature interactions controlling denitrification rates in eroding (Barataria Bay-BLC) and emerging (Wax Lake Delta-WLD) deltaic regions in coastal Louisiana using the isotope pairing (IPT) and N2:Ar techniques. We also assessed differences between total (direct denitrification + coupled nitrification-denitrification) and net (total denitrification minus nitrogen fixation) denitrification rates in benthic and wetland habitats with contrasting %OM and bulk density (BD). Sediment (benthic) and soil (wetland) cores were collected during summer, spring, and winter (2015–2016) and incubated at close to in-situ temperatures (30°C, 20°C, and 10°C, respectively). Denitrification rates were linearly correlated with temperature; maximum mean rates ranged from 40.1–124.1 μmol m−2 h−1 in the summer with lower rates (〈26.2 ± 5.3 μmol m−2 h−1) in the winter seasons. Direct denitrification was higher than coupled denitrification in all seasons. Denitrification rates were higher in WLD despite lower %OM, lower total N concentration, and higher BD in wetland soils. Therefore, in environments with low carbon availability, high denitrification rates can be sustained as long as NO3− concentrations are high (〉30 μM) and water temperature is 〉10°C. In coastal Louisiana, substrates under these regimes are represented by emergent supra-tidal flats or land created by sediment diversions under oligohaline conditions (〈1 ppt).

Description: This study was supported by the NOAA-Sea Grant Program-Louisiana (Grant 2013R/E-24) to Victor H. Rivera-Monroy and Kanchan Maiti. Victor H. Rivera-Monroy was also supported by the Department of the Interior South-Central Climate Adaptation Science Center (Cooperative Agreement #G12AC00002).

Description: Dataset: Sediment grain size and radiometric data

Description: Sediments of the northwestern Gulf of Mexico were analyzed for grain size and radiometric data (210-Pb, 234-Th, and 7-Be) to assess Hurricane Harvey impacts. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/825252

Description: NSF Division of Ocean Sciences (NSF OCE) OCE-1760648

Description: Dataset: Stable Isotopes in Reactive Si Pools

Description: Stable isotopes in reactive silica pools of Mississippi River plume sediments collected aboard the R/V Pelican in May 2017 For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/786508

Description: NSF Division of Ocean Sciences (NSF OCE) OCE-1558957