Monday, March 10, 2014

Emily Hladky's Internship, Spring 2014 - Part 4

How did oil from the Deepwater Horizon oil spill reach the sea floor? For the next two weeks, I will be talking about the two current hypotheses that explain how oil reached the seafloor and affected benthic foraminiferal communities.

According to NOAA’s calculated Oil Budget, 17% of the spilled oil was directly recovered from the well head, 13% was naturally dispersed, 23% was evaporated or dissolved, 16% was chemically dispersed, 5% burned, and 3% skimmed at the surface, leaving about 23% of oil unaccounted for (Lohr et al., 2010), which could have fallen to the sea floor, greatly effecting benthic foraminifera. With more recent evidence, it is believed that about 60% of oil released reached the surface and 40% of oil and dispersant is unaccounted for (Brooks et al., In Press). There are many ways that oil from either the surface or plumes could have reached the seafloor, leading to two hypotheses that could explain the deposition of hydrocarbons on the seafloor: the “flocculent blizzard” hypothesis and the “bathtub ring” hypothesis (Schwing et al., In Press; Brooks et al., In Press).

This week I will talk about the “flocculent blizzard” hypothesis. The “flocculent blizzard” hypothesis describes the aggregation and flocculation of hydrocarbon particles and other component particles that form marine snow (Passow et al., 2012). Marine snow is very sticky and collects both organic and inorganic particles in the surrounding area and as it moves throughout the water column (Brooks et al., In Press). Once the marine snow loses its buoyancy, it rapidly sinks to the sea floor, where it covers the top of the sediments (Passow et al., 2012; Brooks et al., In Press) and could have lethal effects, including gradual suffocation of benthic organisms (Passow et al., 2012), specifically benthic foraminifera (Schwing et al., In Press). If the “flocculent blizzard” hypothesis is true, large amounts of a combination of organic matter and oil would have fallen to the sea floor, increasing respiration and therefore decreasing oxygen. Foraminifera that had not previously adapted to anoxia would not have been able to survive long periods without oxygen, though tolerance limits for foraminiferal species to oxygen are not clearly understood (Sen Gupta and Machain-Castillo, 1992). Once these deep sea communities are affected, they may be very slow to recolonize and could take years for full recovery (Montagna et al., 2013).

Next week I will talk about the “bathtub ring” hypothesis!

References: 

Brooks, G.R., Larson, R.A., Flower, B., Hollander, D., Schwing, P.T., Romero, I., Moore, C., Reichart, G.-J., Jilbert, T., Chanton, J., Hastings, D., In Press. Sedimentation Pulse in the NE Gulf of Mexico Following the 2010 DWH Blowout

Montagna, P.A., Baguley, J.G., Cooksey, C., Hartwell, I., Hyde, L.J., Hyland, J.L., Kalke, R.D., Kracker, L.M., Reuscher, M., Rhodes, A.C.E., 2013. Deep-Sea Benthic Footprint of the Deepwater Horizon Blowout. PLoS ONE 8, 1-8.

Passow, U., Ziervogel, K., Asper, V., Diercks, A., 2012. Marine snow formation in the aftermath of the Deepwater Horizon oil spill in the Gulf of Mexico. Environmental Research Letters 7, 11 pp.

Schwing, P.T., Flower, B.P., Romero, I.C., Brooks, G.R., Hastings, D.W., Larson, R.A., Hollander, D.J., In Press. Effects of the Deepwater Horizon Oil Blowout on Deep Sea Benthic Foraminifera in the Northeastern Gulf of Mexico, pp. 1-22.

Sen Gupta, B.k., Machain-Castillo, M.L., 1992. Benthic foaminifera in oxygen-poor habitats. Elsevier Science Publishers B.V., Amsterdam, Marine Micropaleontology, pp. 183-201.  

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Emily Hladky - St. Petersburg, FL

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