Ninth international conference on - Marum

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CH 4 [µmol/L]
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Abstracts of oral presentations
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Fig. 2: Methane concentrations obtained by the membrane inlet mass spectrometer Inspectr 200-200 in surface
waters around two Pockmarks. The high scan rate of 1.3 seconds allows a very detailed consideration of the
horizontal as well as vertical concentration field of CH4 around the pockmarks.
References:
Short R. T., Toler S. K., Kibelka G. P. G., Rueda Roa, D. T., Bell, R. J., Byrne, R. H. (2006). Detection and
quantification of chemical plumes using a portable underwater membrane introduction mass
spectrometer. TrAC, Trends Anal. Chem. 25 (7), 637–646
Wenner P.G., Bell P. G., van Amerom, F.H.W., Toler S.K., Edkins J.E., Hall M.L., Koehn K., Short R.T. and
Byrne, R.H. (2004). Environmental chemical mapping using an underwater mass spectrometer. Trends
in Analytical Chemistry, 23, 288-295.
Evidence of submarine gas hydrate deposits in context with methane seepage and active venting
on the Hikurangi margin, NZ, from marine controlled source electromagnetics
K. Schwalenberg 1 , I. Pecher 2 , J. Poort 3 , R. Coffin 4 , W. Wood 5 , M. Jegen 6
1 Federal Institute for Geosciences and Natural Resources, Stilleweg 2, 30655 Hannover, GERMANY
2 Institute of Petroleum Engineering, Heriot Watt University, Edinburgh, EH14 4AS, UK
3 Laboratoire de Geosciences Marines, Institut de Physique du Globe de Paris, 7505 Paris, FRANCE
4 Naval Research Laboratory, Marine Biogeochemistry, Overlook Avenue, SW, Washington DC, 20375, USA
5 Naval Research Laboratory, Stennis Space Center, Mississippi 39529, USA,
6 IFM-GEOMAR, Wischhofstr. 1-3, 24148 Kiel, GERMANY
Methane seepage from the seafloor and the existence of submarine gas hydrates is known from the Hikurangi
Margin on the east cost of New Zealand’s North Island. Widespread BSR’s have been observed in seismic data
and several gas seep sites have been identified with echo sounders and video observations during expeditions on
New Zealand’s RV Tangaroa. The first systematic investigation of methane seepage took place in 2006 on cruise
TAN0607 and culminated in the <strong>international</strong> multidisciplinary “New Vents” project in 2007 on RV Sonne
cruise SO191.
Marine controlled source electromagnetics (CSEM) is an exploration method that recently gained considerable
recognition in the offshore oil and gas exploiting industry. This is because the electrical resistivity derived from
CSEM data is sensitive to the presence of resistive hydrocarbons such as oil, gas, and also gas hydrates.
Submarine gas hydrates form in the available pore space of the sediment matrix and replace conductive pore
fluid, with the consequence that the observed resistivity increases over areas, where hydrate forms in sufficient
quantities.
Within the “New Vents” project it was the first time that marine CSEM has been applied within a German
project as well as in New Zealand coastal waters. Four profiles have been served in three target areas of known
venting and methane seepage. The instrumentation used is a unique bottom-towed electric dipole-dipole system,
capable to sense the seafloor to a depth of some hundred meters with a lateral resolution of about 100m. Three
profiles show a strong coincidence between the location of seep sites and very anomalous resistivities. Deposits
of concentrated gas hydrate at depth are likely the cause for these anomalies, but free gas may also play a role. In
particular, data from the Wairarapa at the SE corner of the North Island point to considerable sources of gas
hydrates in the first 100mbsf. There is one seep site where active venting, high heat flow, shallow gas hydrate
recovered from cores, and seismic fault planes have been observed, but no resistivity anomaly. The reasons