Babbin Andrew

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Babbin
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Andrew
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  • Article
    Nitrite oxidation exceeds reduction and fixed nitrogen loss in anoxic Pacific waters
    (Elsevier, 2020-08-20) Babbin, Andrew ; Buchwald, Carolyn ; Morel, Francois M. M. ; Wankel, Scott D. ; Ward, Bess B.
    The diversity of nitrogen-based dissimilatory metabolisms in anoxic waters continues to increase with additional studies to the marine oxygen deficient zones (ODZs). Although the microbial oxidation of nitrite (NO2–) has been known for over a century, studies of the pathways and microbes involved have generally proceeded under the assumption that nitrite oxidation to nitrate requires dioxygen (O2). Anaerobic NO2– oxidation until now has been conclusively shown only for anammox bacteria, albeit only as a limited sink for NO2– in their metabolism compared to the NO2– reduced to N2. Here, using direct experimental techniques optimized for replicating in situ anoxic conditions, we show that NO2– oxidation is substantial, widespread, and consistent across the ODZs of the eastern tropical Pacific Ocean. Regardless of the specific oxidant, NO2– oxidation rates are up to an order of magnitude larger than simultaneous N2 production rates for which these zones are known, and cannot be explained by anammox rates alone. Higher rates of NO2– oxidation over reduction in anoxic waters are paradoxical but help to explain how anammox rates can be enhanced over denitrification in shallow anoxic waters (σθ < 26.4) at the edge of the ODZs but not within the ODZ core. Furthermore, nitrite oxidation may be the key to reconciliation of the perceived imbalance of the global fixed nitrogen loss budget.
  • Article
    Discovery and quantification of anaerobic nitrogen metabolisms among oxygenated tropical Cuban stony corals
    (Springer Nature, 2020-12-20) Babbin, Andrew ; Tamasi, Tyler ; Dumit, Diana ; Weber, Laura ; Rodríguez, María Victoria Iglesias ; Schwartz, Sarah L. ; Armenteros, Maickel ; Wankel, Scott D. ; Apprill, Amy
    Coral reef health depends on an intricate relationship among the coral animal, photosynthetic algae, and a complex microbial community. The holobiont can impact the nutrient balance of their hosts amid an otherwise oligotrophic environment, including by cycling physiologically important nitrogen compounds. Here we use 15N-tracer experiments to produce the first simultaneous measurements of ammonium oxidation, nitrate reduction, and nitrous oxide (N2O) production among five iconic species of reef-building corals (Acropora palmata, Diploria labyrinthiformis, Orbicella faveolata, Porites astreoides, and Porites porites) in the highly protected Jardines de la Reina reefs of Cuba. Nitrate reduction is present in most species, but ammonium oxidation is low potentially due to photoinhibition and assimilatory competition. Coral-associated rates of N2O production indicate a widespread potential for denitrification, especially among D. labyrinthiformis, at rates of ~1 nmol cm−2 d−1. In contrast, A. palmata displays minimal active nitrogen metabolism. Enhanced rates of nitrate reduction and N2O production are observed coincident with dark net respiration periods. Genomes of bacterial cultures isolated from multiple coral species confirm that microorganisms with the ability to respire nitrate anaerobically to either dinitrogen gas or ammonium exist within the holobiont. This confirmation of anaerobic nitrogen metabolisms by coral-associated microorganisms sheds new light on coral and reef productivity.
  • Dataset
    CTD data from 9 casts at the oxygen-deficient zone of the Eastern Tropical North Pacific (ETNP), RV/Atlantis cruise AT37-12, April-May 2017
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-01-03) Sievert, Stefan M ; Babbin, Andrew
    CTD data from Atlantis cruise AT37-12 in the Eastern Tropical North Pacific in April and May 2017. Data from 9 casts are included. 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/739098
  • Dataset
    CTD log at the oxygen deficient zone of the Eastern Tropical North Pacific (ETNP) for RV/Atlantis cruise AT37-12, April-May 2017
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-12-09) Sievert, Stefan M ; Babbin, Andrew
    A total of 10 CTD casts were performed on AT37-12 focusing on sampling the waters of the oxygen deficient zone of the Eastern Tropical North Pacific (ETNP). Cast 7 could not be completed due to problems with the wire. This dataset reports the station, date, location, water depth and sampling depth of individual Niskin bottles. 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/738001