Carbon isotope (δsup13/supC) excursions suggest times of major methane release during the last 14 kyr in Fram Strait, the deep-water gateway to the Arctic

摘要

We present results from a sediment core collected from a pockmark field onthe Vestnesa Ridge (~ 80° N) in the eastern Fram Strait.This is the only deep-water gateway to the Arctic, and one of thenorthernmost marine gas hydrate provinces in the world. Eight 14C AMSdates reveal a detailed chronology for the last 14 ka BP. The δ13C record measured on the benthonic foraminiferal speciesCassidulina neoteretis shows two distinct intervals with negative values termed carbon isotopeexcursion (CIE I and CIE II, respectively). The values were as low as?4.37‰ in CIE I, correlating with theB?lling–Aller?d interstadials, and as low as ?3.41‰in CIE II, correlating with the early Holocene. In the B?lling–Aller?dinterstadials, the planktonic foraminifera also show negative values,probably indicating secondary methane-derived authigenic precipitationaffecting the foraminiferal shells. After a cleaning procedure designed toremove authigenic carbonate coatings on benthonic foraminiferal tests fromthis event, the 13C values are still negative (as low as?2.75‰). The CIE I and CIE II occurred during periodsof ocean warming, sea-level rise and increased concentrations of methane(CH₄) in the atmosphere. CIEs with similar timing have been reportedfrom other areas in the North Atlantic, suggesting a regional event. Thetrigger mechanisms for such regional events remain to be determined. Wespeculate that sea-level rise and seabed loading due to high sediment supplyin combination with increased seismic activity as a result of rapiddeglaciation may have triggered the escape of significant amounts of methaneto the seafloor and the water column above.