Award: PLR-1023281

Methane is about 35 times as potent at trapping heat as carbon dioxide, and a huge amount of it is stored as methane hydrates. A significant fraction of hydrates was predicted to be preserved in the Arctic shelf. Because Arctic hydrates are permafrost-related, as the climate warms these deposits can be destabilized, with major climatic repercussions (Fig.1). The East Siberian Arctic Shelf (ESAS) composes >25% of the Arctic shelf and hosts >80% of currently existing sub-sea permafrost and permafrost-related marine hydrates (Fig.2). The methane-rich ESAS encompasses more than 2 million square kilometers of seafloor in the Arctic Ocean – it is the broadest and shallowest shelf in the World Ocean and is more than three times as large as the nearby Siberian wetlands, which have been considered the primary Northern Hemisphere source of atmospheric methane. This shelf has been experiencing drastic warming of up to 17?C caused by its inundation with sea water during the last few thousand years. Nevertheless, until recently it was unknown whether sub-sea permafrost had started to degrade and therefore to allow significant leakage of methane from the ESAS to the atmosphere. It is important to gain this knowledge because: The amount of methane preserved in the ESAS as methane hydrates is thought to be huge (two to three orders of magnitude higher than the modern methane atmospheric burden); thus, the contribution to the global emission budget would be significant; the destabilization of methane hydrates causes a tremendous increase in the volume and pressure of releasing gaseous methane, which could lead to abrupt methane bursts with implications for climate warming feedbacks; and, the majority of methane from the ESAS escapes directly to the atmosphere because fluxes occur predominantly as bubbles of gas; this reduces the residential time in the shallow water column (mean depth is <50 m) to tens of seconds, which is too short a time for methane to be oxidized before it escapes to the atmosphere. Key accomplishments: New investigations of methane release from the ESAS in order to assess methane flux rates and temporal-spatial variability over time (seasonal and inter-annual variability) were accomplished in several summer and winter expeditions with partial support from this project (Figs. 3, 4). Complex biogeochemical, geophysical, and geological techniques were applied. Key findings: 1. Annual methane fluxes from the ESAS, which composes only ~1% of the World Ocean area, currently contribute at least as much to the global methane emissions as does the entire World Ocean (Fig.5; Shakhova et al., 2010ab). 2. Subsea permafrost has started to lose its integrity via formation of migration pathways for bubbles releasing from the sea floor. This process determines an annual contribution of at least 9 Tg methane to a revised annual atmospheric ESAS flux of 17 Tg methane (Shakhova et al., 2014), which is six times more than that from the Siberian wetlands 3. Rates of methane release range over five orders of magnitude is associated with presumably different degrees of sub-sea permafrost degradation. This implies substantial potent emission enhancement in the ESAS. 4. Data demonstrate that storm-induced ventilation of the water column serves as a very efficient mechanism to transfer dissolved methane to the atmosphere (Shakhova et al., 2014). Given predictions of an increase in the already-high Arctic storm frequency, drastic ice shrinkage, and warming of sea water, it is important to assess overall bubbling and storm-mediated methane emissions from the Arctic seas. 5. Our improvements to the modeling algorithm have allowed better agreement between the spatial distribution of high dissolved-methane concentrations and areas of projected taliks (Fig. 6) Future challenges/needs The potential of climate change to destabilize Arctic shallow hydrates has significant implications both for the global climate and for Arctic ecosystems. The ESAS is experiencing the most significant warming in the Arctic region and the highest levels of atmospheric concentration of methane have recently been observed over the ESAS (Shakhova et al., 2010ab, 2014). The amount of methane that could theoretically be released from decaying hydrate deposits in future episodic events could be enormous. Nevertheless, the initial assessment of annual methane emissions from the Arctic shelf was incomplete because many emission components were set to zero for lack of constraints. Specifically, while strong pulses of methane releases have been documented, the contribution from such ebullition fluxes was not considered due to the unknown spatial/temporal pattern of such fluxes. Moreover, because a key factor in determining methane emissions from the Arctic shelf is sub-sea permafrost, investigation of the current state of sub-sea permafrost is crucially important to any assessment of future emission enhancement. List of selected project papers: Shakhova et al., (2014) Nature Geosciences, vol. 7, No. 1, doi: 10.1038/NGEO2007 Shakhova et al. Science 327, 1246-1250 Shakhova et al., Journal Geophys. Res 115, doi:10.1029/2009JC005602, 2010 Nicolsky, D., and N. Shakhova (2010). Env. Res. Lett.,5, doi:10.1088/1748-9326/5/1/015006. Last Modified: 11/26/2014 Submitted by: Natalia Shakhova