Deepwater Horizon hydrocarbons entered the Gulf of Mexico food web

Deepwater Horizon hydrocarbons entered the Gulf of Mexico food web
The CTD being lowered over the side of a research ship in the Gulf of Mexico. This piece of equipment was a vital part of this study- each bottle is used to collect a sample of water at a specific depth in the water column. This gave ECOGIG researchers the ability to collect samples above, in and below the deepwater plume that formed as a result of the spill. (c) ECOGIG

December 14, 2016

Microscopic organisms in the water, such as bacteria, use oil and gas as a food source- these organisms are called hydrocarbon degrading microbes. There are hundreds of natural oil and gas seeps in the Gulf of Mexico, creating the perfect environment for these organisms. The Deepwater Horizon accident in 2010 released an unprecendented amount of oil and gas into the Gulf of Mexico. After the accident, it was found that the abundance of the hydrocarbon degrading microbes increased significantly, in response to the large amount of petrocarbon (carbon from oil and gas, their food source) in the water. The number and activity of these organisms remained high until at least December of 2010. These microbes make up an important piece of the Gulf of Mexico food web- the petrocarbon that they consume gets incorporated up the food chain as other larger organisms consume them.

The petrocarbon released in the accident was made up of carbon depleted in carbon 13 and carbon 14 isotopes (forms of the same element that have small differences in their weight). ECOGIG researchers were able to trace the movement of this petrocarbon into the Gulf of Mexico food web using stable isotope analysis (a method of comparing the amount of heavyweight carbon to the amount of lightweight carbon in a sample). Research cruises were conducted by ECOGIG scientists in 2010, 2011 and 2012 to collect samples and study the incorporation of this petrocarbon into the Gulf of Mexico food web. They also sought to confirm whether the carbon was still present in the food web one and two years after the spill. Through this study, researchers confirmed that oil and gas from the accident were incorporated into the Gulf of Mexico food web- in some places the oil and gas contributed up to 62% and 28% of the carbon, respectively. They also confirmed that oil from the spill was still present in the food web two years afterwards.

The oil and gas released from the well after the accident formed surface slicks as well as a deep water plume (1000-1200 meters below the surface of the Gulf). Through their stable isotope analysis, ECOGIG researchers were able to detect the presence of oil as far as 289 kilometers (approximately 180 miles) southwest of the Deepwater Horizon well, in water depths of 1000-1200 meters. This was the first time that researchers had direct evidence of the far reaching extent of the deepwater plume.

This work from ECOGIG researchers serves to contribute to the work documenting the quick response in both the activity and composition change of the Gulf's microbial community after the Deepwater Horizon accident. This work confirms the presence of petrocarbons in the Gulf food web and their persistence two years after the spill. It's also the first study to provide direct evidence of the plume hundreds of kilometers southwest of the wellhead.

You may access the entire paper, titled "Deep Water Horizon oil and methane carbon entered the food web in the Gulf of Mexico" online here.

To read more about the research being done by ECOGIG scientists on microbial community activities in the Gulf, visit our web page on microbial community dynamics.

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