Aggregation and Degradation of Dispersants and Oil by Microbial Exopolymers 2 (ADDOMEx-2): Towards a synthesis of process and pathways of marine oil snow formation
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abstract
The work proposed here will build on the previous findings of ADDOMEx. Specifically, research during ADDOMEx identified many of the bacteria and phytoplankton responsible for the copious production of transparent exopolymeric particles (TEP), exopolymeric substances (EPS), marine snow and marine oil snow (MOS) in the presence and absence of oil (as a water accommodated fraction; WAF), the dispersant Corexit, and Corexit-dispersed oil (as a chemically enhanced water accommodated fraction, CEWAF, and as a diluted form, herein called DCEWAF). The factors that influence or retard the subsurface scavenging of oil into MOS were determined and ongoing research is beginning to pinpoint the processes that promote decomposition of the oil post MOS formation. This improved understanding has expanded our ability to predict the behavior and footsteps of released oil, and the potential impacts of Corexit application, specifically with respect to Marine Oil Snow (MOS) processes (e.g., formation, fate). The following insights were gained during ADDOMEx but are not yet in current conceptual or numerical models: 1) reactive oxygen species (ROS; produced by sunlight or enzymes) mediate crosslinking of proteins in EPS to form aggregates. 2) details of the processes that control interactions between Corexit, oil and EPS in producing either sinkable MOS or dispersed gels promoting microbial degradation of oil compounds. 3) rapid oil oxidation and microbial degradation in water within a few days of exposure, especially at the surface of the ocean, and 4) rapid formation of microbial aggregates on oil droplets is enhanced in the presence of Corexit-dispersed oil. The next step is thus to integrate ADDOMEx derived insights into a comprehensive conceptual model framework. Key experiments will generate measurements needed to improve numerical modeling (in conjunction with FOMOSA and others) which will enhance prediction capabilities in order to guide the decision process of first responders. The primary experimental goal of ADDOMEx-2 is to perform a series of “wrap-up” experiments intended to fill current knowledge gaps. All proposed experiments will be conducted and samples analyzed within year 1. These experiments will center around two main hypotheses:(1) Particle formation and fragmentation is governed mainly by stickiness.(2) The fate of oil (chemically undispersed or Corexit dispersed) trapped within MOS is dictated by both chemical and microbial oxidation. Both processes lead to rapid oxidative alteration of the oil. This affects the sinking and dispersion of MOS and the associated oxidized oil. Sub-hypotheses will address further the mechanisms of the growth of nano- to micro- to macrogels and their role in dispersing oil, the factors that control MOS sedimentation, and the role of light versus microbially produced ROS in oxidation and crosslinking of MOS aggregates. Furthermore, ADDOMEx-2 includes three critical synthesis-based activities...........
