Prokopenko Maria

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Prokopenko
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Maria
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  • Dataset
    Eastern Tropical South Pacific Nitrogen fixation
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2015-04-16) Knapp, Angela ; Casciotti, Karen L. ; Berelson, William M. ; Prokopenko, Maria ; Capone, Douglas
    An extensive region of the Eastern Tropical South Pacific (ETSP) Ocean has surface waters that are nitrate-poor yet phosphate-rich. It has been proposed that this distribution of surface nutrients provides a geochemical niche favorable for N2 fixation, the primary source of nitrogen to the ocean. Here, we present results from two cruises to the ETSP where rates of N2 fixation and its contribution to export production were determined with a suite of geochemical and biological measurements. N2 fixation was only detectable using nitrogen isotopic mass balances at two of six stations, and rates ranged from 0 to 23 µmol N m-2 d-1 based on sediment trap fluxes. Whereas the fractional importance of N2 fixation did not change, the N2-fixation rates at these two stations were several-fold higher when scaled to other productivity metrics. Regardless of the choice of productivity metric these N2-fixation rates are low compared with other oligotrophic locations, and the nitrogen isotope budgets indicate that N2 fixation supports no more than 20% of export production regionally. Although euphotic zone-integrated short-term N2-fixation rates were higher, up to 100 µmol N m-2 d-1, and detected N2 fixation at all six stations, studies of nitrogenase gene abundance and expression from the same cruises align with the geochemical data and together indicate that N2 fixation is a minor source of new nitrogen to surface waters of the ETSP. This finding is consistent with the hypothesis that, despite a relative abundance of phosphate, iron may limit N2 fixation in the ETSP.
  • Dataset
    Gridded in-situ profiles from glider deployments in the San Pedro Channel, CA in 2013 and 2014
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-05-28) Teel, Elizabeth N. ; Jones, Burton ; Haskell, William ; Prokopenko, Maria ; Hammond, Douglas ; Levine, Naomi M
    This dataset includes chlorophyll a fluorescence and water temperature from gridded in-situ profiles from a slocum glider deployed between March and July in 2013 and 2014 in the San Pedro Channel, located in the Southern California Bight off the coast of Los Angeles. 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/751128
  • Dataset
    Measurements of dissolved organic nitrogen concentration and d15N from R/V Atlantis and R/V Melville cruises in the Eastern Tropical South Pacific from 2010 to 2011.
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-03-19) Knapp, Angela ; Casciotti, Karen L. ; Prokopenko, Maria
    Measurements of dissolved organic nitrogen concentration and d15N from R/V Atlantis and R/V Melville cruises in the Eastern Tropical South Pacific from 2010 to 2011. 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/729480
  • Dataset
    Gridded in-situ oxygen profiles from glider deployments in the San Pedro Channel, CA in 2013 and 2014
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-10-02) Haskell, William ; Hammond, Douglas ; Prokopenko, Maria ; Jones, Burton ; Levine, Naomi M ; Teel, Elizabeth N.
    Gridded in-situ oxygen profiles from glider deployments in the San Pedro Channel, CA in 2013 and 2014. 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/768685
  • Preprint
    Anaerobic diagenesis of silica and carbon in continental margin sediments : discrete zones of TCO2 production
    ( 2005-05-10) Berelson, William M. ; Prokopenko, Maria ; Sansone, F. J. ; Graham, A. W. ; McManus, Jerry F. ; Bernhard, Joan M.
    Pore water profiles of dissolved Si, Ca2+, SO42-, CH4, and TCO2 (Dissolved Inorganic Carbon; DIC) were determined from multicores and gravity cores collected at nine sites off Southern California, the west coast of Mexico, and within the Gulf of California. These sites were located within the eastern North Pacific oxygen minimum zone at depths of 400 to 900 m and in settings where bottom water oxygen concentrations were <3 μM and sediments were laminated. Pore water profiles were defined at a resolution of millimeters (whole core squeezing), centimeters (sectioning and squeezing) and meters (gravity core sectioning and squeezing), and diffusive fluxes were calculated for different zones within the sediment column. The flux of dissolved silica across the sediment-water interface (SWI) ranged from 0.3 to 3.4 mmol Si m-2d-1, and TCO2 fluxes ranged from 0.8 to 4.6 mmol C m-2d-1. A positive correlation (r = 0.74) existed between these fluxes, yet these two constituents exhibited significantly different diagenetic behavior downcore; dissolved Si generally reached a constant concentration (between 450 and 900 μM) in the upper few cm, whereas TCO2 concentrations increased monotonically with depth. Methane was detected at micromolar levels in sediment intervals between 0 and 60 cm and at five sites, increased to millimolar levels at depths of 80 to 170 cm. At the horizon marking the appearance of millimolar levels of methane, there was a distinct change in slope of the sulfate and TCO2 gradients. A flux budget for this horizon was determined by using linear fits to pore water profiles; these budgets indicate that the upward TCO2 flux away from this horizon is 40 to 50% greater than the downward sulfate flux to this horizon. Given that the TCO2 flux to this horizon from below was quite small, this imbalance suggests that anaerobic oxidation of methane by sulfate is not the only process producing TCO2 within this horizon. A budget for TCO2 at this horizon is balanced when 40 to 80% of the sulfate flux is attributed to organic carbon remineralization. Of the DIC that diffuses across the SWI, 20 to 40% is generated by reactions occurring within or below this deep reaction horizon.