Online membrane inlet mass spectrometry (Inspectr200-200) for quantification of the methane concentration
field around Pockmarks
Torben Gentz
1, Michael Schlüter
11
Alfred Wegener Institute for Polar and Marine Research
CH4 [µmol/l]
0.0 0.2 0.4 0.6 0.8 1.0
Intensity m/z=15 [Amps]
2.0e-11 4.0e-11 6.0e-11 8.0e-11 1.0e-10 1.2e-10 1.4e-10 1.6e-10 1.8e-10 2.0e-10 2.2e-10
y = 1.910E-10x + 2.956E-11 R2 = 0.9960
1. Calibration of methane
2. Comparison Inspectr200-200 to gas chromatograph
Lake Constance; March 08
The sampling frequency is 750 times higher to the established method
Results: Check-list of requirements
3-D Profiling
^_ ^_
Friedrichshafen
Rorschach
Hard Friedrichshafen
Lindau
Fußach
Rheineck
Bad Schachen
Lindau Wasserburg
Langenargen Friedrichshafen
Kressbronn am Bodensee
Nonnenhorn
Staad
Altenrhein Eriskirch
Langenargen
Kressbronn am Bodensee
Legend
Methane concentration Lake Constance [µmol/l]
CH4_1vo
-0,029000 - 0,093000 0,093001 - 0,207000 0,207001 - 0,318000 0,318001 - 0,394000 0,394001 - 0,533000
0 1.250 2.500 5.000Meters
Results: Concentration field of methane around Pockmarks (Lake Constance)
0 2.5 5 10Meters
^ _PM80
0 2.5 5 10Meters
^ _PM80
0 2.5 5 10Meters
^ _PM80
0 2.5 5 10Meters
^ _PM80
CH4 (32-600 nM) at 70m water depth CH4 (30-150 nM) at 50m water depth
CH4 (30-120 nM) at 5 m water depth CH4 (90-180 nM) at 1 m water depth
+
+
Methane distribution at different levels at a Pockmark
(Measurements along a 15m*25m grid)
Inspectr200-200 (AML)
Detection of steep concentration fields of methane around pockmarks and other
hotspots of CH4 seepage requires:
1. Calibration within a wide range of CH4 concentration and a detection limit of
<50nmol
2. Results comparable with established techniques like gas chromatography 3. High sampling frequency and fast
response time
4. In-situ measurement to cope with sampling artifacts
Why Inspectr200-200
Problems:
-Sampling artifacts (de- pressurisation),
-time consuming,
-coarse spatial and temporal resolution
-low sampling rate
Established method
Water colum and sediment sampling
Phase separation (gas phase from aqueous phase):
Headspace technique for
analysis of discrete samples
Gas analysis by gas
chromatography
Compared to such semi-quantitative information, rather little-known is the concentration field of CH4 as well as other gases around e.g. pockmarks. This is mainly to the laborious sampling schemes and rather time consuming CH4 analysis by gas chromatography.
.. often the CH4 concentrations around “hot
spots” are rather low.
Visual observation of the
release of gas bubbles from the seafloor.
Acoustic “image” of gas bubble plumes in the water column.
Worldwide, the release of methane from sediments of lakes, coastal regions as well as ocean margins is observed. The
gas release is often associated with specific features like pockmarks (morphological depressions at the seafloor), mud volcanoes, cold seeps as well as occurrence of gas hydrates.
For such sites gas plumes were observed by underwater camera systems as well as acoustic techniques.
The motivation of our work is the spatial and temporal distribution analysis of Methane
around Pockmarks and other CH
4seeps
Acoustic blanking in surface sediments
Chemoautotrophic organisms
Bottom Water Sampler Sauter et al., 2002
Application of MIMS is a step towards a more detailed investigation of spatial and temporal variations of methane in aquatic systems
3. Response time
y = 0,980x + 26,88 R² = 0,979
0 500 1000 1500 2000 2500
0,0 1000,0 2000,0 3000,0
Gas chromatograph Methane[nmol/l]
Mass Spectrometer Methane [nmol/l]
Green Pockmark detection
High resolution see below
