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 SleeperChemical Sensors Group, Marine Technology ProgramSt. Petersburg, Florida

Earth Ocean and Atmospheric Science, Florida State University

Seabed Technology Research Center, Mississippi Mineral Resources Institute, University of Mississippi

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

Depth Profile Data – Gulf of MexicoBefore spill 03/11/2009

Argon Corrected

UMS Deployment at MC118 (June 24, 2010)

4

MC252

Cast 1

Cast 2

Cast 4

Vertical Dissolved Gas Profiles at MC118

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Methane

Nitrogen

Argon

Down Cast Up Cast

Mas

s S

pect

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eter

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nal I

nten

sity

(A

rb)

Time (min)0 15 30

Vertical Methane Concentration Profiles at MC118

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Cast 1 Cast 2 Cast 3

Methane profiles June 2010

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methane nM

dept

h, m

Cast 13

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Cast 15

MC-118

d13C of CH4 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‰

CTD228° 51.1949 88° 29.4040

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CH4 concentration (nM)

de

pth

be

low

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a s

urf

ace

(m

)

Profile at MC-118 September 2010

-46.8 ‰

Hydrocast over MC-118 seep site July 2009

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0.0 20.0 40.0 60.0 80.0 100.0

nM methane

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

CTD over Charlie Seep, MC 118, July 2009

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0.0 10.0 20.0 30.0 40.0 50.0

nM methane

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BACKGROND site at MC 118,

CTD over CC BKG at MC 118

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0.0 5.0 10.0 15.0

nM methane

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th m

CC BKG site MC 118

• 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 d13C 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