Late Quaternary Atmospheric CH4 Isotope Record Suggests Marine Clathrates Are Stable

Department of Geosciences and the Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802, USA.
Science (Impact Factor: 33.61). 02/2006; 311(5762):838-40. DOI: 10.1126/science.1121235
Source: PubMed


One explanation for the abrupt increases in atmospheric CH4, that occurred repeatedly during the last glacial cycle involves clathrate destabalization events. Because marine clathrates
have a distinct deuterium/hydrogen (D/H) isotope ratio, any such destabilization event should cause the D/H ratio of atmospheric
CH4 (δDCH4) to increase. Analyses of air trapped in the ice from the second Greenland ice sheet project show stable and/or decreasing
δDCH4 values during the end of the Younger and Older Dryas periods and one stadial period, suggesting that marine clathrates were
stable during these abrupt warming episodes. Elevated glacial δDCH4 values may be the result of a lower ratio of net to gross wetland CH4 emissions and an increase in petroleum-based emissions.

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Available from: Todd Anthony Sowers
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    • "The validity of this " clathrate gun hypothesis " is contentious. Methane emissions from wetlands may exceed those from gas hydrates hosted in marine sediments, as suggested by isotopic analysis of methane within ice core records (Sowers, 2006). Here we consider whether our two study locations provide evidence that landslides may have helped to drive climate change through methane emissions. "
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    • "Ferretti et al., 2005; Fischer et al., 2008; Sowers, 2010; Sapart et al., 2012; Möller et al., 2013) provide further insight into processes and sources controlling the global methane cycle. For instance, knowledge of the temporal evolution of the hydrogen isotopic composition of methane (δD(CH 4 ) or δ 2 H(CH 4 )) over the termination of the last ice age (14 000– 18 000 years before present) (Sowers, 2006) as well as during rapid warming events between 32 000–42 000 years before present (Bock et al., 2010b) made it possible to reject the " clathrate gun hypothesis " proposed by Kennett et al. (2003) as the trigger for the steep atmospheric methane increases. However, we are still far from a complete picture of the biogeochemistry of methane in the past. "
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    • "Insights into the source of atmospheric methane from deuterium isotopes within ice cores provide the most unambiguous evidence against landslides (or indeed gas hydrates in marine sediments more generally) being a cause of climate change (Sowers, 2006). "
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    ABSTRACT: Submarine landslides on open continental slopes can be prodigious in scale. They are an important process for global sediment fluxes, and can generate very damaging tsunamis. Submarine landslides are far harder to monitor directly than terrestrial landslides, and much greater uncertainty surrounds their preconditioning factors and triggers. Submarine slope failure often occurs on remarkably low (< 2°) gradients that are almost always stable on land, indicating that particularly high excess pore pressures must be involved. Earthquakes trigger some large submarine landslides, but not all major earthquakes cause widespread slope failure. The headwalls of many large submarine landslides appear to be located in water depths that are too deep for triggering by gas hydrate dissociation. The available evidence indicates that landslide occurrence is either weakly (or not) linked to changes in sea level or atmospheric methane abundance, or the available dates for open continental slope landslides are too imprecise to tell. Similarly, available evidence does not strongly support a view that landslides play an important role in methane emissions that cause climatic change. However, the largest and best-dated open continental slope landslide (the Storegga Slide) coincides with a major cooling event 8,200 years ago. This association suggests that caution may be needed when stating that there is no link between large open slope landslides and climate change.
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