WP5 Geofluids and gas hydrates

WP leader: Jürgen Mienert, University of Tromsø, Norway
Angelo Camerlenghi, University of Barcelona, Spain

All global climate change scenarios (with CO2 concentration increasing to at least 500 ppm) forecast a large and irreversible change in Arctic Ocean regions. Coupled ocean – atmosphere modeling predicts already significant warming of shallow Arctic seas by several degrees Celsius for surface-waters by the year 2050. Recent marine geophysical research has identified various methane hydrate provinces in Arctic regions, and determined some bounds such as ocean temperature for their thermodynamic stability. New discoveries at the seabed and beneath show vigorous methane venting from gas chimneys where the hydrate outcrops. Understanding the effects of climate change on the Arctic region and its sensitive ecosystems in general, and on the stability of gas hydrate and release of geofluids in particular, is therefore both an urgent scientific challenge and of high societal relevance.

The highly debated clathrate gun hypothesis states that natural gas (mostly CH4) emissions from gas hydrate dissociation, induced by bottom water warming during interstadials, occur primarily via methane seepage from the seafloor. The mechanisms of transfer of gas within fluid escape chimneys from the submarine geosphere to the hydrosphere, however, are not understood. Where gas hydrates are stable, they play a role as buffer for methane seepage and thus may prevent gas releases into the hydrosphere. Environmental changes such as increasing bottom water temperature have been claimed to trigger gas hydrate dissociation or dissolution with subsequent escapes of gas to the water column and atmosphere at a regional scale, resulting in a positive feedback mechanism of global relevance. Upward gas migration happens primarily through narrow sub-vertical conduits imaged acoustically as “chimneys” or “pipes”, whose seafloor expressions are often “pockmarks”. Even if the gas release is primarily triggered by the sudden un-roofing of gas and gas-hydrate charged sediments the gas transfer is thought to occur via conduits identified in giant (several kilometer in diameter) or small (several 10 to 100m in diameter) chimneys that connect to blow-out craters or pockmarks at the seabed.

At the seabed, methane or hydrocarbon seeps increase the biological activity as well documented by the EC-funded HERMES project (Hotspot Ecosystem Research on the Margin of European Seas). Today’s knowledge suggests that individual seeps may show a zonation of the ecosystem related to both the strength of the methane flux and biogeochemical processes in near surface sediments. Common build-ups in many seeps are the formation of authigenic carbonate pavements that are preserved after burial. These formations exhibit various morphologies depending on chimney size and construction. The hard substrates at the surface are often colonised by characteristic seep fauna. Gas hydrate dissociation could play a significant role where methane contributes to sustain seep-related chemosynthetic communities over several thousand years.

Natural hydrocarbon seeps including CH4 release are numerous in continental margin settings of Europe. Today’s global warming scenario has put the Arctic regions as one of the most important areas for environmental research. It has >1 million km2 of shallow sea areas and millions of pockmarks and fluid release structures, and is responding rapidly to climate change. In order to evaluate the contribution of marine sediments to the atmospheric methane globally, it is of fundamental importance to determine the frequency of CH4 emissions from the seafloor through time. Atmospheric CH4 concentrations through time recorded in ice cores do not reveal unequivocally the source of methane, so that the breakdown of the geological emissions of methane and the role of organisms consuming and producing methane is one of the major tasks for future studies.

Recent research has demonstrated the sensitivity of foraminiferal communities (differences in taxonomic structures and abundance) to methane emissions and gas hydrate dissociation. Similarly, stable isotope geochemistry shows that the carbonate of foraminiferal tests in areas of methane release and gas hydrate dissociation is characterised by distinctly negative delta 13C values. However, the data obtained so far have never been used to evaluate emission of methane regionally or even globally, although this method could be relevant in assessing paleo-methane emissions. Ongoing studies on pockmarks, submarine landslides and fossil methane emissions suggest that the carbon isotopic composition of benthic foraminifera can indeed be employed as a proxy of methane emissions from the seafloor. Thus, there is compelling evidence from recent records that drilling into selected fluid-escape chimneys will increase our understanding in climate, environmental, energy and ecosystem research. However, such a drilling campaign has yet to be developed. One of the primary goals of this WP is therefore to develop the program for conducting scientific drilling into and long-term observation of gas chimneys and other gas escape pathways, coring for various geochemical and biological parameters characteristic for natural methane release systems, and to develop synergies with ocean observation programs such as ESONET, EMSO, and NEPTUNE (USA-Canada) or DONET (Japan). A concentration on fluid escape chimney studies in continental margins of the Arctic is envisioned but other areas are necessary as well to understand the full spectrum from giant to smaller scale fluid-release chimneys.

The central science objective of WP5 is to determine whether there is a causative effect of warming shallow Arctic seas conducting heat into seafloor and sub-seafloor sediments at such a rate that the thermodynamic stability field of methane hydrate will be perturbed, increasing the release of free and dissolved CH4 gas into the ocean. In this context, the impacts of methane release on benthic ecosystems and ocean biogeochemical cycles will be assessed. Causal relationships between climate change and catastrophic CH4 release were proposed for the geological past and for changes in atmospheric methane in the future, and therefore Arctic drilling missions are needed at key locations. Drilling into key fluid release chimneys has never been done before, but it is of regional and global relevance providing opportunities for fundamental, forefront interdisciplinary research involving geophysics and geology, geochemistry, biogeochemistry, microbiology and biology in times of global climate change.

List of tentative WP5 participants (Level 3)

A. Boetius, AWI, Bremerhaven, Germany (Microbial processes); M. Hovland, StatoilHydro, Stavanger, Norway (Seabed fluid flow); E. S. Andersen, StatoilHydro, Oslo, Norway (Gas Hydrate); G. Panieri, Univ. Bologna, Italy (13C isotopes); H.Løseth, StatoilHydro, Trondheim, Norway (Gas Chimneys); M.Huuse, Kings College, Aberdeen, UK (Sed. Deformation); A. Mazzini, Univ. Oslo, Norway (Chemosynth. communities); G. Etiope, INGV, Roma, Italy (CH4 – Observatories); C. Berndt, IfM-GEOMAR Kiel, Germany (Seismic Imaging), S. Bünz, Univ. Tromsø, Norway (Seismic imaging); I. Wright, NOCS, Southampton, UK (CH4 – Observatories); M. de Batist, Univ. Ghent, Belgium (Gas Hydrates); J. Greinert, NIOZ, Netherlands (Fluid Flow); T. Feseker, IfM-GEOMAR Kiel, Germany (Heat flow); J.L. Charlou, IFREMER, France (Geochemistry/Fluids); D. de Beer, MPI-MM, Germany (HMMV, ESONET); T. Minshull, NOCS, UK (Seismic Modelling); T. M. Hill, Univ. California Santa Barbara, USA (13C isotopes); B. Dugan, Rice Univ., USA (Hydrological models); G. Dickens; Rice Univ., USA (Global Carbon cycle).