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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 - PowerPoint PPT Presentation
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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
6
Methane
Nitrogen
Argon
Down Cast Up Cast
Mas
s S
pect
rom
eter
Sig
nal I
nten
sity
(A
rb)
Time (min)0 15 30
Vertical Methane Concentration Profiles at MC118
7
Cast 1 Cast 2 Cast 3
Methane profiles June 2010
0
100
200
300
400
500
600
700
800
900
1000
0 200 400 600 800 1000 1200 1400 1600 1800 2000
methane nM
dept
h, m
Cast 13
Cast 14
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
0
100
200
300
400
500
600
700
800
900
1000
0 20 40 60 80 100 120
CH4 concentration (nM)
de
pth
be
low
se
a s
urf
ace
(m
)
Profile at MC-118 September 2010
-46.8 ‰
Hydrocast over MC-118 seep site July 2009
0
200
400
600
800
1000
0.0 20.0 40.0 60.0 80.0 100.0
nM methane
dept
h m
Generally maximum associated with seeps at MC 118 are lesser concentrationThan we’ve observed this year.
CTD over Charlie Seep, MC 118, July 2009
0
200
400
600
800
1000
0.0 10.0 20.0 30.0 40.0 50.0
nM methane
dept
h m
BACKGROND site at MC 118,
CTD over CC BKG at MC 118
0
100
200
300
400
500
600
700
800
900
1000
0.0 5.0 10.0 15.0
nM methane
dep
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