The irruption of gas and oil into the Gulf of Mexico during the Deepwater Horizon event fed a deep sea bacterial bloom that consumed hydrocarbons in the affected waters, formed a regional oxygen anomaly, and altered the microbiology of the region. In this work, we develop a coupled physical-metabolic model to assess the impact of mixing processes on these deep ocean bacterial communities and their capacity for hydrocarbon and oxygen use. We find that observed biodegradation patterns are well-described by exponential growth of bacteria from seed populations present at low abundance and that current oscillation and mixing processes played a critical role in distributing hydrocarbons and associated bacterial blooms within the northeast Gulf of Mexico. Mixing processes also accelerated hydrocarbon degradation through an autoinoculation effect, where water masses, in which the hydrocarbon irruption had caused blooms, later returned to the spill site with hydrocarbon-degrading bacteria persisting at elevated abundance. Interestingly, although the initial irruption of hydrocarbons fed successive blooms of different bacterial types, subsequent irruptions promoted consistency in the structure of the bacterial community. These results highlight an impact of mixing and circulation processes on biodegradation activity of bacteria during the Deepwater Horizon event and suggest an important role for mixing processes in the microbial ecology of deep ocean environments.oil spill | well blowout | intrusion layers O il and gas from the Macondo well flowed freely into the deep Gulf of Mexico for a period of 83 d after the explosion and sinking of the Deepwater Horizon (DWH) mobile offshore drilling unit. The environmental release of crude oil occurred at ∼1.5 km water depth with an estimated magnitude of 4.1 × 10 6 barrels (1). Large volumes of gas also emanated from the ruptured well, with reported ratios of gas to oil ranging from 1,600 to 2,800 standard cubic feet of gas (15.6°C, 1 bar) per barrel of oil (2-4). Mass fluxes estimated from these values are 5.4 × 10 11 g for liquid oil and 1.8-3.1 × 10 11 g for natural gases, defined here as alkanes with one to five carbons.Oil and gas entered the ocean initially through multiple openings in the ruptured riser pipe and later, from the top of the blowout preventer after the riser pipe was cut away on June 1, 2010 (1). The hydrocarbon droplets ejected ranged in size from several millimeters down to small droplets with slow ascent rates; 771,000 gal dispersant were applied at depth to promote formation of such small, slow-rising droplets. On release, the bulk of oil and gas began a rapid ascent from the sea floor, entraining sea water as it rose. The entrainment of sea water cooled the oil and gas rapidly (3) and initiated both dissolution of the soluble components and formation of gas hydrate. Kinetically controlled chemical fractionation seems to have persisted for several hundred meters of ascent until the entrained waters separated from the ascending oil (3, 5, 6). These waters f...

This paper considers a problem of area coverage where the objective is to achieve given coverage density by use of multiple mobile agents. We present an ergodicity-based coverage algorithm which enables a centralized feedback control for multiagent system based on radial basis function (RBF) representation of the ergodicity problem and a solution of an appropriately designed stationary heat equation for the potential field. The heat equation uses a source term that depends on the difference between the given goal density distribution and the current coverage density (time average of RBFs along trajectories). The agent movement is directed using the gradient of that potential field. The heat equation driven area coverage has a built-in cooperative behavior of agents which includes collision avoidance and coverage coordination. The algorithm is robust, scalable, and computationally inexpensive.

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