Project

ocean sediments; porewater; solute transport; Ocean sediment; pore water; noble gas geochemistry; helium isotopes; methane seepage; centrifugation

Lead
Lay summary
Noble gas geochemistry in the pore water of lacustrine sediments is an growing research field where different studies already demonstrated the potential of the latter to track environmental changes such as lake level and salinity fluctuations or to determine the geochemical source of the fluids dissolved in the water trapped in the pore space.In this project we aim to expand our analytical skills to the sediments from the oceans. However the actual standard procedure developed five years ago for the extraction of noble gases from the pore water of unconsolidated sediments does not apply to the oceanic sediments because of the compact sediment structure, which often hampers the required “blow out” at 150°C of the sediment/water mixture from the sampling containers into an extraction vessel.We intend to bypass this problem by centrifugation of the sediment samples. Through a successful separation of a part of the water content of the sediment samples, it is possible to measure the noble gas content in the water phase with the standard protocol used for normal water samples.This work will be carried out on samples from the Pacific Ocean off shore New Zealand, where an active methane seepage is present. On one hand we expect to be able for the first time ever to measure noble gases in ocean sediment samples. On the other hand we will characterize the geochemical reservoir which is responsible for methane emanation.

Direct link to Lay Summary

Last update: 21.02.2013

Number	Title	Start	Funding scheme

Although recently noble gases in pore water of lacustrine sediments allow the successful determination of lake level and salinity fluctuations, the reconstruction of past environmental conditions, and the eutrophic state of the lake water bodies, ocean sediments are still not assessable by presentexperimental techniques.In this project that is intended to cover the last year of the PhD thesis of Yama Tomonaga we aim to overcome restrictions that still severely limit the application of noble gases in unconsolidated sediments from the ocean.The up to now used experimental protocols for the quantitative noble gas determination out of pore waters of sediments ultimately ask for the complete exhalation of sediment-water mélange into extraction vessel from where the noble gases are extracted. This experimental challenge probably explain why the noble gas group at ETHZ/Eawag is still the only group that can carry out such analysis.We head to bypass the experimental limits by simplify the experimental protocol to extract noble gases from sediment pore waters. We suggest to separate the pore water and the sediment matrix by centrifugation of the unconsolidated sediment within the sample container (for details seebehind). After centrifugation the water phase is sealed off from the “dewatered” sediment matrix and is extracted in second step as a “pure water” sample following the well accepted standard protocols of noble gas extraction from waters. The suggested new method for the determination of noble gas in pore waters will be applied for the first time ever to sedimentsfrom Pacific Ocean off shore New Zealand to analyze fluid transport and methane emission in active CH4 seeps.