Changes in Redox Conditions of Surface Sediments Following the Deepwater Horizon and Ixtoc 1 Events

David W. Hastings, Thea Bartlett, Gregg Brooks, Rebekka A. Larson, Kelly A. Quinn, Daniel Razionale, Patrick Schwing, Libia Hascibe Pérez Bernal, Ana Carolina Ruiz-Fernández, Joan-Albert Sánchez-Cabeza, David Hollander

Research output: Chapter in Book/Report/Conference proceedingChapter

Abstract

<p> <p id="x-x-Par1"> Following the blowout of the Macondo well, a sedimentation pulse resulted in significant changes in sedimentary redox conditions. This is demonstrated by downcore and temporal changes in the concentration of redox-sensitive metals: Mn and Re. Sediment cores collected in the NE Gulf of Mexico reveal increased sedimentation after the <em> Deepwater Horizon </em> (DWH) blowout. The formation of mucous-rich marine snow in surface waters and subsequent rapid deposition to sediments is the likely cause. Respiration of this material resulted in decreased pore-water oxygen and a shoaled redoxcline, resulting in two distinct Mn peaks in sediments following the event, one typically in the top 5&ndash;7 mm, with the other at 20&ndash;30 mm. Cores near the wellhead reveal this nonsteady-state behavior for 3&ndash;5 years after the event. A time series reveals that bulk sediment Re increased 3&ndash;4 times compared to the pre-impact baseline value for 2&ndash;3 years indicating sediments are increasingly more reducing. Three years after the blowout, subsurface Re reaches a plateau suggesting a return to steady-state conditions. In select sites where benthic foraminifera were counted, an assemblage-wide decrease is coincident with reducing conditions, demonstrating the important consequences of changing redox conditions on benthic ecosystems. <p id="x-x-Par2"> Another major submarine blowout in the southern Gulf of Mexico (Ixtoc 1; 1979&ndash;1980) released a large volume of crude oil below the surface. We observe multiple Mn oxide peaks associated with a shoaling redoxcline and Re maxima associated with more reducing conditions. Nonsteady-state behavior at sites near DWH and Ixtoc 1 is consistent with a MOSSFA (marine oil snow sedimentation and flocculent accumulation) event at both locations. </p> </p></p>
Original languageAmerican English
Title of host publicationDeep Oil Spills Facts, Fate, and Effects
DOIs
StatePublished - Jun 1 2019

Keywords

  • Oil spill
  • Gulf of Mexico
  • Deepwater Horizon
  • Redox
  • Trace metal
  • Rhenium
  • Manganese

Disciplines

  • Life Sciences
  • Marine Biology

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