Wednesday, March 26, 2014

Emily Hladky's Internship, Spring 2014 - Part 5

How did oil from the Deepwater Horizon oil spill reach the sea floor? Last week, I talked about the “flocculent blizzard” hypothesis which, for review, describes the aggregation and flocculation of hydrocarbon particles and other component particles which forms marine snow (Passow et al., 2012). When the marine snow sinks, it covers the top sediments, having lethal effects (Passow et al., 2012; Brooks et al., In Press), often gradual suffocation of benthic organisms (Passow et al., 2012).

This week I will be talking about the second hypothesis of how the oil reached the sea floor: the “bathtub ring” hypothesis. To give you a brief background, when the oil was released from the well, it was released at a depth of about 1500 meters. When oil is released at great depth it is under high pressure (~160 atm) and low temperature (4°C), which causes it to act differently than oil at the surface (Thibodeaux et al., 2011). The substance released from the wellhead contained many soluble hydrocarbons (Ryerson et al., 2012) that dissolved in the water column and remained at depth, forming plumes (Hazen et al., 2010; Valentine et al., 2010). Two plumes were detected: one deep, persistent plume between 1000-1200 meters deep and a slightly shallower plume between 800-1000 meters deep, northeast of the wellhead (Passow et al., 2012; Valentine et al., 2010).

The “bathtub ring” hypothesis describes the movement of these plumes through the water column; these plumes come in direct contact with the sediment surface causing lethal and sub-lethal effects, most likely a sudden mortality event caused by the toxic hydrocarbons (Schwing et al., In Press). With this hypothesis, the heaviest impacted areas would be expected to occur where the plumes are located (Brooks et al., In Press), between 800-1000 meters and between 1000-1200 meters, which has been seen in some studies. The sudden presence of toxic hydrocarbons would have had a dramatic impact on foraminifera that had not previously been adapted to the presence of hydrocarbons.

Both hypotheses are believed to have occurred and both had negative effects on most benthic foraminifera, though there are some species that are adapted or considered opportunistic species, which are species that take advantage of abundant food and are able to thrive in lower oxygen environments (Sen Gupta and Machain-Castillo, 1992). Though some species flourish, there was a great decrease in the number of benthic foraminifera present after the spill. Hopefully in the next few weeks I will have more data and we will be able to determine which hypothesis affected the sites and how they are recovering.

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

Hazen, T.C., Dubinsky, E.A., DeSantis, T.Z., Andersen, G.L., Piceno, Y.M., Singh, N., Jansson, J.K., Probst, A., Borglin, S.E., Fortney, J.L., Stringfellow, W.T., Bill, M., Conrad, M.E., Tom, L.M., Chavarria, K.L., Alusi, T.R., Lamendella, R., Joyner, D.C., Spier, C., Baelum, J., Auer, M., Zemla, M.L., Chakraborty, R., Sonnenthal, E.L., D'Haeseleer, P., Holman, H.-Y.N., Osman, S., Lu, Z., Van Nostrand, J.D., Deng, Y., Zhou, J., Mason, O.U., 2010. Deep-Sea Oil Plume Enriches Indigenous Oil-Degrading Bacteria. Science, 204.

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.

Ryerson, T.B., Camilli, R., Kessler, J.D., Kujawinski, E.B., Reddy, C.M., Valentine, D.L., Atlas, E., Blake, D.R., de Gouw, J., Meinardi, S., Parrish, D.D., Peischl, J., Seewald, J.S., Warneke, C., 2012. Chemical data quantify Deepwater Horizon hydrocarbon flow rate and environmental distribution. Proceedings of the National Academy of Sciences of the United States of America 109, 20246-20253.

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.

Thibodeaux, L.J., Valsaraj, K.T., John, V.T., Papadopoulos, K.D., Pratt, L.R., Pesika, N.S., 2011. Marine Oil Fate: Knowledge Gaps, Basic Research, and Development Needs; A Perspective Based on the Deepwater Horizon Spill. Environmental Engineering Science 28, 87-93.

Valentine, D.L., Kessler, J.D., Redmond, M.C., Mendes, S.D., Heintz, M.B., Farwell, C., Hu, L., Kinnaman, F.S., Yvon-Lewis, S., Du, M., Chan, E.W., Tigreros, F.G., Villanueva, C.J., 2010. Propane Respiration Jump-Starts Microbial Response to a Deep Oil Spill. Science, 208  

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Emily Hladky - St. Petersburg, FL

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