Monterey Bay Aquarium Research Institute
AUVs
AUV in the Gulf of Mexico

MBARI was called on to help following the 2010 catastrophic oil spill in the Gulf of Mexico, where the Deepwater Horizon, a drilling rig, exploded and a damaged wellhead leaked vast amount of oil.

An MBARI AUV was deployed from the National Oceanic and Atmospheric Administration (NOAA) ship Gordon Gunter in Mississippi on the morning of May 28, 2010. The AUV had the distinct advantage of being able to go deep into the ocean whereas satellites and planes could only take pictures of the ocean's surface.

MBARI researchers lower AUV into Gulf of Mexico
MBARI's water sampling AUV is lowered from the NOAA vessel Gordon Gunter into the Gulf of Mexico. © MBARI 2010

This MBARI AUV dove up to 1,500 meters (5,000 feet) below the surface, which was deep enough to collect water samples near the seafloor in the vicinity of the oil spill.

The MBARI vehicle proved useful in understanding the effects of the Gulf oil spill. Information about possible hidden oil plumes allowed researchers to grasp a better understanding of the effects the oil had on the surrounding environment.


MBARI/NOAA Preliminary Data Report

During May 27th to June 4th, 2010 MBARI participated in a cruise to investigate subsurface oil near the BP Deepwater Horizon wellhead. MBARI was interested in mapping, sampling, and analyzing the subsurface hydrocarbon plumes to determine their distributions and how they interact with the oceanic environment. MBARI's Dorado-class AUV is capable of quickly surveying and sampling an area deep under the ocean, which proved critical for sampling important subsurface features near the Deepwater Horizon wellhead. MBARI was sponsored by the National Oceanic and Atmospheric Administration (NOAA) and conducted its AUV operations from the NOAA ship Gordon Gunter.

This report is a summary of sensor data collected from the AUV survey from June 2nd to June 3rd. Optical and chemical measurements have indicated a detection of hydrocarbon in plume like features below 1000 meters deep. The data will be used to create a method of distinguishing specific signals of the oil plume from the rest of the ocean. Physical samples from the plume-like feature were also acquired from the AUV and the Gordon Gunter's sampling systems. NOAA is managing the shore-based laboratory analyses of these physical samples. When the results from the physical samples are available, researchers should be able to better interpret the plume-like feature including: concentration range, chemical composition, and its source (wellhead or natural seafloor seepage).

Satellite image of the AUV surveys near the BP Deepwater Horizon
The blue highlighted circle indicates the location of the June 2-3 MBARI AUV surveys relative to the BP Deepwater Horizon site. © MBARI 2010

The AUV used its sensors to measure the following variables in the plume-like feature:

  • temperature
  • salinity
  • pressure
  • density
  • dissolved oxygen concentration
  • colored dissolved organic matter (CDOM)
  • optical backscattering (at 420 and 700 nm)
  • Chlorophyll fluorescence at 700 nm (420 nm excitation).

The AUV surveyed at about five nautical miles southwest of the Deepwater Horizon wellhead as indicated by the image below. The AUV was deployed to this specific site in response to NOAA scientists on the vessel detecting high CDOM signals in the area that were between 1100 and 1200 meters deep. The AUV specifically mapped and sampled a deep volume of oceanic water ranging from 900 to 1200 meters deep. It surveyed this area in a series of vertical sections. After each section, the AUV would come up to the surface for a global positioning system (GPS) fix, which allowed for it collect data from 900 meters to the surface of the ocean.

Trail the AUV mapped in the volume of ocean water

The map to the left shows the Deepwater Wellhead (red triangle) location relative to the area of the AUV survey (grey rectangle). The reference 1 M stands for one nautical mile. The center map shows that the AUV conducted two deep water sections on June 2nd. The right map shows that the AUV conducted seven sections during the June 3rd survey., the green circle showing where the AUV started, the cyan lines showing where the AUV traveled below 900 meters, and the numbers representing the order of which the AUV conducted the surveys. © MBARI 2010

graph showing the concentration of color dissolved organic matter in the Gulf of Mexico

Graph showing the concentration of CDOM fluorescence in relative fluorescence units (rtf). © MBARI 2010

Colored dissolved organic matter (CDOM) findings

Along with other researchers who are investigating the Deepwater Horizon oil spill, MBARI used CDOM fluorescence, which can indicate possible hydrocarbons beneath the ocean's surface. All of the data that were acquired by the CDOM fluorometer during the AUV surveys from June 2nd to June 3rd are shown in the image to the right. The graph shows that as the AUV goes deeper into the ocean, the maximum amount of CDOM linearly increases. The red line is an extrapolation of the expected linear trend in the CDOM fluorescence concentration. However, from 1,000 to 1,200 meters, the expected maximum linear trend does not occur, as indicated by the sudden increase in CDOM fluorescence.

These results of significant features found below 1,000 meters were consistent with other research efforts in the Gulf of Mexico region. They help indicate that the depth concentration of significant features of hydrocarbons. Autonomous underwater vehicles have proved to be valuable in sampling these features since they can reach depths that other mobile and fixed platforms cannot reach.

Three-dimensional model of significant feature of interest

The June 3rd survey provided dense sampling measurements within the target volume. The AUV acquired more than 65,000 CDOM measurements along the seven sections ranging from 900 to 1,200 meters deep. MBARI and NOAA researchers were able to compile a three-dimensional model of the significant feature of interest by using chemical and optical properties found in the vertical secions.

 

Illustration shows the significant plume of interest that was analyzed by the Dorado-class AUV on June 3rd. The brown colored hues represent the colors of the colored dissolved organic matter. The deepwater horizon wellhead is five miles northwest of the volume that the AUV surveyed. © MBARI 2010

 


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Last updated: Dec. 04, 2013