1. Characterization of Light Hydrocarbons by Underwater Membrane Introduction Mass Spectrometry, Contros Sensor and Traditional Gas Chromatography R. Timothy Short, Ryan Bell, Rachel Wilson, Jeff Chanton and Ken Sleeper Chemical Sensors Group, Marine Technology Program St. Petersburg, Florida Earth Ocean and Atmospheric Science, Florida State University Seabed Technology Research Center, Mississippi Mineral Resources Institute, University of Mississippi

2. UMS for Hydrates Research in the Gulf of Mexico Vertical profiles of dissolved gases with UMS in Gulf of Mexico (MC118) UMS mounted on custom frame along with conductivity, temperature, and depth (CTD), dissolved oxygen (DO), and pH sensors Communicated with instrument through standard UNOLS CTD tether using Seabird modem Determined dissolved gas concentrations from UMS data with the aid of a portable calibration unit

3. Depth Profile Data – Gulf of Mexico Before spill 03/11/2009 Argon Corrected

4. UMS Deployment at MC118 (June 24, 2010) 4 MC252

5. Cast 1 Cast 2 Cast 4

6. Vertical Dissolved Gas Profiles at MC118 6 Methane Nitrogen Argon Down Cast Up Cast Time (min) 0 15 30

7. Vertical Methane Concentration Profiles at MC118 7 Cast 1 Cast 2 Cast 3

8. MC-118  13 C of CH 4 at maximum = -53.8 ± 1.3‰ (n=5) similar to values obtained on Walton Smith Cruise in May, 2010 -57.4 ± 0.5 ‰ Methane at MC-118 has previously been determined to be -46 to -47‰

9. Profile at MC-118 September 2010 -46.8 ‰

10. Generally maximum associated with seeps at MC 118 are lesser concentration Than we’ve observed this year.

12. BACKGROND site at MC 118,

13. This year we have consistently observed maxima in dissolved methane concentration at 600m depth over MC 118, about 8 km north of MC-252. In past years, methane profiles collected directly over vents at MC118 show deeper maxima, and background profiles away from the vents show no deep maxima at all. Conclusions: This year concentration profiles are distinctly different from past years. Methane  13 C at MC-118 is -47‰ or more positive. Methane at the maximum observed in water column profiles at MC-118 in 2010 is -53.8 ‰ ± 1.3 ‰ similar to values observed in water column samples collected “downstream” of MC-252 in May on the Walton Smith Cruise -57.4 ± 0.5‰ (Joye and Chanton, unpublished data). Funding received from U.S. Department of Energy through the Gulf of Mexico Gas Hydrates Consortium