Igor Semiletov

Extensive Methane Venting to the Atmosphere from Sediments of the East Siberian Arctic Shelf

Bubble, Bubble, Warming and Trouble Vast quantities of methane are stored in ocean sediments, mostly in the form of clathrates, but methane is also trapped in submerged terrestrial permafrost that was flooded during the last deglaciation. There is thus concern that climate warming could warm ocean waters enough to release methane cryogenically trapped beneath the seabed, causing even more warming. Shakova et al. (p. 1246; see the Perspective by Heimann) report that more than 80% of the bottom water, and more than 50% of the surface water, over the East Siberian Arctic Shelf, is indeed supersaturated with methane that is being released from the sub-sea permafrost, and that the flux to the atmosphere now is as great as previous estimates of that from the entire world ocean. Methane emissions from this region of sub-sea permafrost are comparable to previous estimates for the world ocean. Remobilization to the atmosphere of only a small fraction of the methane held in East Siberian Arctic Shelf (ESAS) sediments could trigger abrupt climate warming, yet it is believed that sub-sea permafrost acts as a lid to keep this shallow methane reservoir in place. Here, we show that more than 5000 at-sea observations of dissolved methane demonstrates that greater than 80% of ESAS bottom waters and greater than 50% of surface waters are supersaturated with methane regarding to the atmosphere. The current atmospheric venting flux, which is composed of a diffusive component and a gradual ebullition component, is on par with previous estimates of methane venting from the entire World Ocean. Leakage of methane through shallow ESAS waters needs to be considered in interactions between the biogeosphere and a warming Arctic climate.

Contrasting lipid biomarker composition of terrestrial organic matter exported from across the Eurasian Arctic by the five great Russian Arctic rivers

Contrasting lipid biomarker composition of terrestrial organic matter exported from across the Eurasian Arctic by the five great Russian Arctic rivers

Pan-Arctic patterns in black carbon sources and fluvial discharges deduced from radiocarbon and PAH source apportionment markers in estuarine surface sediments

[1]xa0A pan-arctic geospatial picture of black carbon (BC) characteristics was obtained from the seven largest arctic rivers by combining with molecular combustion markers (polycyclic aromatic hydrocarbons) and radiocarbon (14C) analysis. The results suggested that the contribution from modern biomass burning to BC ranged from low in the Yukon (8%) and Lena (5%) Rivers to high in the Yenisey River (88%). The Mackenzie River contributed almost half of the total arctic fluvial BC export of 202 kton a−1 (kton = 109 g), with the five Russian-Arctic rivers contributing 10–36 kton a−1 each. The 14C-based source estimate of fluvially exported BC to the Arctic Ocean, weighted by the riverine BC fluxes, amount to about 20% from vegetation/biofuel burning and 80% from 14C-extinct sources such as fossil fuel combustion and relict BC in uplifted source rocks. Combining these pan-arctic data with available estimates of BC export from other rivers gave a revised estimate of global riverine BC export flux of 26 × 103 kton a−1. This is twice higher than a single previous estimate and confirms that river export of BC is a more important pathway of BC to the oceans than direct atmospheric deposition.

Deposition Settings on the Continental Shelf of the East Siberian Sea

The spacious continental shelf of the East Siberian Sea (ESS) is of particular interest primarily due to its formation in settings of periglacial lithogenesis. This region is characterized by the universal development of Pleistocene permafrost rocks (PFR) [1, 11]. The presence of thick veins of relict ice enclosed in these sequences determined the dependence of the coastalshelf cryolithozone PFR on the thermal and hydrodynamic impact. Under the influence of these factors, the present-day coastal zone is advancing landward at an annual mean rate of 3‐5 m. Consequently, the seawater occupies tens of square kilometers of the former coastal areas of maritime plains [2, 3, 6, 12]. Large volumes of mineral and organic material introduced into shelf waters become involved in sedimentary and biogeochemical cycles. The ESS shelf is known not only for such catastrophic natural processes. It hosts the largest explored and potential reserves of coastalmarine placers and is considered a part of the megaba

The great Siberian rivers as a source of methane on the Russian Arctic shelf

The methane marine cycle in the Arctic region has not received due attention thus far, since the role of the Arctic Ocean in the global methane cycle was widely held to be insignificant by the scientific community. At the same time, some authors have clearly shown that this role seems to have been substantially underestimated [1‐3]. The Arctic Ocean represents not only a giant petroliferous superbasin enclosing huge reserves of natural hydrocarbons, but also an estuary of the world’s largest rivers, the drainage systems of which are underlain by thick layers of permafrost hosting enormous reserves of organic carbon. Degradation of permafrost and involvement of old organic carbon into the present-day biochemical cycle determine, to a large measure, the role of Arctic marine ecosystems and others in both the regional and global methane cycles. In this connection, study of the role of great Siberian rivers as methane sources on the Russian Arctic shelf is especially topical.

Chlorophyll Response to Shelf-Break Upwelling and Winds in the Chukchi Sea, Alaska, in Autumn

In the Chukchi Sea, autumn 1996 was windier than most of the previous 35 years. Conditions in the Bering Strait were anomalous, with fresh coastal water absent from the Strait and a partial flow reversal apparently occurring. In the central Chukchi Sea, the northeastward flow of the Alaskan Coastal Current was reversed. In the northern Chukchi Sea, upwelling of offshore, high-nutrient upper halocline waters inundated much of the shelf near Barrow Canyon. The resulting chlorophyll blooms indicate dramatically enhanced ecosystem productivity along this northern shelf region. With increasing climatic change occurring in this region, shelf break productivity would likely increase in the future.