Paleo‐methane emissions recorded in foraminifera near the landward limit of the gas hydrate stability zone offshore western Svalbard

Abstract

We present stable isotope and geochemical data from four sediment cores from west of Prins Karls Forland (ca. 340 m water depth), offshore western Svalbard, recovered from close to sites of active methane seepage, as well as from shallower water depths where methane seepage is not presently observed. Our analyses provide insight into the record of methane seepage in an area where ongoing ocean warming may be fueling the destabilization of shallow methane hydrate. The d13 C values of benthic and planktonic foraminifera at the methane seep sites show distinct intervals with negative values (as low as 227.8&) that do not coincide with the present-day depth of the sulfate methane transition zone (SMTZ). These intervals are interpreted to record long-term fluctuations in methane release at the present-day landward limit of the gas hydrate stability zone (GHSZ). Shifts in the radiocarbon ages obtained from planktonic foraminifera toward older values are related to methane-derived authigenic carbonate overgrowths of the foraminiferal tests, and prevent us from establishing the chronology of seepage events. At shallower water depths, where seepage is not presently observed, no record of past methane seepage is recorded in foraminifera from sediments spanning the last 14 ka cal BP ( 14 C-AMS dating). d 13 C values of foraminiferal carbonate tests appear to be much more sensitive to methane seepage than other sediment parameters. By providing nucleation sites for authigenic carbonate precipitation, foraminifera thus record the position of even a transiently stable SMTZ, which is likely to be a characteristic of temporally variable methane fluxes.

Resistivity image beneath an area of active methane seeps in the west Svalbard continental slope

“…Submersible dives have revealed colonies of methane consuming bacteria along with authigenic carbonate deposits around the 400 m isobath (Berndt et al 2014). These deposits and recent geochemical analysis (Panieri et al 2016) suggest the presence of long term methane seepage in the area. Hydrate dissociation in response to seasonal variation in bottom water temperatures (1-2…”

Magnetic Mineralogical Approach for the Exploration of Gas Hydrates in the Bay of Bengal

“…Rock magnetic studies of gas hydrate environments have focused primarily on understanding diagenetic alteration of detrital magnetic minerals (Dewangan et al, ; Enkin et al, ; Esteban et al, ; Johnson & Phillips, ; Riedinger et al, ; Shi et al, ), exploring linkages between magnetic iron sulfides and gas hydrates (Housen & Musgrave, ; Kars & Kodama, , b; Larrasoaña et al, ; Musgrave et al, ), deciphering controls on gas hydrate system evolution (Badesab et al, ), rock magnetic properties of gas hydrate bearing sediments (Kars & Kodama, , b), and developing proxies for tracking paleomethane seepage events (Novosel et al, ; Panieri et al, ; Usapkar et al, ) and paleo sulfate‐methane transition zone (SMTZ) boundaries (Johnson et al, ; Peketi et al, ). However, detailed rock magnetic studies that focus on unravelling linkages between sedimentation, shale‐tectonism, sediment diagenesis, and gas hydrate formation in marine sedimentary systems are still lacking.…”

A record of seafloor methane seepage across the last 150 million years

“…The fit between C1 and MDC before 70 My is excellent, except for a transient in the period 130-140 Ma (r 2 = 0.56). The agreement between the record and model worsens between 0 and 70 My ago (r 2 = 0.12) comprising both a period of amplitude decrease (50-70 Ma) and one of strong variations (40)(41)(42)(43)(44)(45)(46)(47)(48)(49). By adding cyclicity C2, the agreement between record and model is partially restored between 0 and 40 Ma (r 2 = 0.36).…”

“…Despite lipid biomarkers having the potential to record variations of methane through time, they do not provide information on the absolute age when these variations occur and thus their best application is to reconstruct dynamics at local scales. The use of δ 13 C can also be applied to overgrowths of authigenic carbonate on benthic foraminifera tests 43,44 . This method can potentially provide high-resolution records of methane seepage, but its suitability is a subject of current debate 43 .…”