Shah Walter Sunita R.

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Last Name
Shah Walter
First Name
Sunita R.
ORCID
0000-0003-2206-9052

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  • Article
    Rapid extraction of dissolved inorganic carbon from seawater and groundwater samples for radiocarbon dating
    (John Wiley & Sons, 2015-10-29) Gospodinova, Kalina D. ; McNichol, Ann P. ; Gagnon, Alan R. ; Shah Walter, Sunita R.
    We designed and developed a system to efficiently extract dissolved inorganic carbon (DIC) from seawater and groundwater samples for radiocarbon dating. The Rapid Extraction of Dissolved Inorganic Carbon System (REDICS) utilizes a gas-permeable polymer membrane contactor to extract the DIC from an acidified water sample in the form of carbon dioxide (CO2), introduce it to a helium gas stream, cryogenically isolate it, and store it for stable and radiocarbon isotope analysis. The REDICS system offers multiple advantages to the DIC extraction method which has been used for the last several decades at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS) at the Woods Hole Oceanographic Institution, including faster DIC extraction, streamlined analysis, and minimized set-up and prep time. The system was tested using sodium carbonate and seawater standards, duplicates of which were also processed on the water stripping line (WSL) at NOSAMS. The results demonstrate that the system successfully extracts, quantifies, and stores more than 99% of the DIC in less than 20 min. Stable and radiocarbon isotope analysis demonstrated system precision of 0.04‰ and 7.8‰, respectively. A Sargasso Sea depth profile was used to further validate the system. The results show high precision for both stable and radiocarbon analysis with pooled standard deviations of 0.02‰ and 5.6‰, respectively. A comparison between the REDICS and WSL analyses indicates a good accuracy for both stable and radio-isotope analysis.
  • Article
    Ultra-small graphitization reactors for ultra-microscale 14C analysis at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) Facility
    (University of Arizona Libraries, 2015) Shah Walter, Sunita R. ; Gagnon, Alan R. ; Roberts, Mark L. ; McNichol, Ann P. ; Lardie Gaylord, Mary C. ; Klein, Elizabeth
    In response to the increasing demand for 14C analysis of samples containing less than 25 µg C, ultra-small graphitization reactors with an internal volume of ~0.8 mL were developed at NOSAMS. For samples containing 6 to 25 µg C, these reactors convert CO2 to graphitic carbon in approximately 30 min. Although we continue to refine reaction conditions to improve yield, the reactors produce graphite targets that are successfully measured by AMS. Graphite targets produced with the ultra-small reactors are measured by using the Cs sputter source on the CFAMS instrument at NOSAMS where beam current was proportional to sample mass. We investigated the contribution of blank carbon from the ultra-small reactors and estimate it to be 0.3 ± 0.1 µg C with an Fm value of 0.43 ± 0.3. We also describe equations for blank correction and propagation of error associated with this correction. With a few exceptions for samples in the range of 6 to 7 µg C, we show that corrected Fm values agree with expected Fm values within uncertainty for samples containing 6–100 µg C.
  • Article
    Multiple carbon incorporation strategies support microbial survival in cold subseafloor crustal fluids
    (American Association for the Advancement of Science, 2021-04-28) Trembath-Reichert, Elizabeth ; Shah Walter, Sunita R. ; Fontánez Ortiz, Marc Alec ; Carter, Patrick D. ; Girguis, Peter R. ; Huber, Julie A.
    Biogeochemical processes occurring in fluids that permeate oceanic crust make measurable contributions to the marine carbon cycle, but quantitative assessments of microbial impacts on this vast, subsurface carbon pool are lacking. We provide bulk and single-cell estimates of microbial biomass production from carbon and nitrogen substrates in cool, oxic basement fluids from the western flank of the Mid-Atlantic Ridge. The wide range in carbon and nitrogen incorporation rates indicates a microbial community well poised for dynamic conditions, potentially anabolizing carbon and nitrogen at rates ranging from those observed in subsurface sediments to those found in on-axis hydrothermal vent environments. Bicarbonate incorporation rates were highest where fluids are most isolated from recharging bottom seawater, suggesting that anabolism of inorganic carbon may be a potential strategy for supplementing the ancient and recalcitrant dissolved organic carbon that is prevalent in the globally distributed subseafloor crustal environment.
  • Dataset
    Inventory of fluid and filter samples collected for carbon composition and isotope analysis from R/V Atlantis cruise AT39-01 at the North Pond CORK Sites U1382A and U1383C during October 2017
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2021-08-03) Girguis, Peter ; Shah Walter, Sunita R.
    This dataset is an inventory of fluid and filter samples collected for carbon composition and isotope analysis from R/V Atlantis cruise AT39-01 at the North Pond CORK Sites U1382A and U1383C during October 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/723493
  • Dataset
    Concentrations, d13C and D14C data for DOC and DIC in fluids collected from North Pond Cork Observatories U1382A and U1383C and from bottom seawater in 2012, 2014 and 2017.
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-08-10) Girguis, Peter ; Shah Walter, Sunita R.
    Concentrations, d13C and D14C data for DOC and DIC in fluids collected from North Pond Cork Observatories U1382A and U1383C and from bottom seawater in 2012, 2014 and 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/876729