Carbon isotope (δ¹³C) excursions suggest times of major methane release during the last 14 kyr in Fram Strait, the deep-water gateway to the Arctic

• Main Authors: C. Consolaro, T. L. Rasmussen, G. Panieri, J. Mienert, S. Bünz, K. Sztybor
• Format: Article
• Language: English
• Published: Copernicus Publications 2015-04-01
• Series: Climate of the Past
• Online Access: http://www.clim-past.net/11/669/2015/cp-11-669-2015.pdf

We present results from a sediment core collected from a pockmark field on the Vestnesa Ridge (~ 80° N) in the eastern Fram Strait. This is the only deep-water gateway to the Arctic, and one of the northernmost marine gas hydrate provinces in the world. Eight ¹⁴C AMS dates reveal a detailed chronology for the last 14 ka BP. The &delta; ¹³C record measured on the benthonic foraminiferal species <i>Cassidulina neoteretis</i> shows two distinct intervals with negative values termed carbon isotope excursion (CIE I and CIE II, respectively). The values were as low as −4.37&permil; in CIE I, correlating with the Bølling–Allerød interstadials, and as low as −3.41&permil; in CIE II, correlating with the early Holocene. In the Bølling–Allerød interstadials, the planktonic foraminifera also show negative values, probably indicating secondary methane-derived authigenic precipitation affecting the foraminiferal shells. After a cleaning procedure designed to remove authigenic carbonate coatings on benthonic foraminiferal tests from this event, the ¹³C values are still negative (as low as −2.75&permil;). The CIE I and CIE II occurred during periods of ocean warming, sea-level rise and increased concentrations of methane (CH₄) in the atmosphere. CIEs with similar timing have been reported from other areas in the North Atlantic, suggesting a regional event. The trigger mechanisms for such regional events remain to be determined. We speculate that sea-level rise and seabed loading due to high sediment supply in combination with increased seismic activity as a result of rapid deglaciation may have triggered the escape of significant amounts of methane to the seafloor and the water column above.