V. I. Sergienko

On carbon transport and fate in the East Siberian Arctic land?shelf?atmosphere system

This review paper summarizes current understanding of the transport of organic carbon to, and the fate of organic carbon within, the East Siberian Arctic Shelf (ESAS), and of processes determining carbon dioxide (CO2) and methane (CH4) fluxes from the ESAS to the atmosphere achieved from analyzing the data sets obtained on 20 expeditions performed from 1999 to 2011. This study of the ESAS was aimed at investigating how redistribution of old carbon from degrading terrestrial and sub-sea permafrost and from coastal erosion contributes to the carbon pool of the ESAS, how changes in the hydrological cycle of the surrounding land and alteration of terrestrial carbon cycles affect the hydrological and biogeochemical parameters of shelf water masses, and which factors control CH4 and CO2 emissions from the ESAS. This report describes selected results achieved by a developing international scientific partnership that has been crucial at every stage of the study and will be even more important in the future.

The East Siberian Arctic Shelf: towards further assessment of permafrost-related methane fluxes and role of sea ice.

Sustained release of methane (CH4) to the atmosphere from thawing Arctic permafrost may be a positive and significant feedback to climate warming. Atmospheric venting of CH4 from the East Siberian Arctic Shelf (ESAS) was recently reported to be on par with flux from the Arctic tundra; however, the future scale of these releases remains unclear. Here, based on results of our latest observations, we show that CH4 emissions from this shelf are likely to be determined by the state of subsea permafrost degradation. We observed CH4 emissions from two previously understudied areas of the ESAS: the outer shelf, where subsea permafrost is predicted to be discontinuous or mostly degraded due to long submergence by seawater, and the near shore area, where deep/open taliks presumably form due to combined heating effects of seawater, river run-off, geothermal flux and pre-existing thermokarst. CH4 emissions from these areas emerge from largely thawed sediments via strong flare-like ebullition, producing fluxes that are orders of magnitude greater than fluxes observed in background areas underlain by largely frozen sediments. We suggest that progression of subsea permafrost thawing and decrease in ice extent could result in a significant increase in CH4 emissions from the ESAS.

The Contribution of the East Siberian Shelf to the Modern Methane Cycle

Methane-containing sediments, accumulated everywhere along continental margins, are a powerful source of atmospheric methane, the third (after carbon dioxide and water vapors) most significant greenhouse gas. Meanwhile, until recently, scientific literature lacked data on the contribution of arctic continental margins to the formation of the global methane budget, as well as realistic forecast scenarios of future climate changes. The results of five-year-long (2003–2007) biogeochemical studies on the East Siberian shelf, which characterize the main arctic methane sources and reservoirs, including unique shelf gas hydrates, are presented in the article below. The studies were conducted by researchers of the Pacific Institute of Oceanology, RAS Far Eastern Division, with the participation of researchers of the International Arctic Research Center of the University of Alaska, Fairbanks.

The degradation of submarine permafrost and the destruction of hydrates on the shelf of east arctic seas as a potential cause of the “Methane Catastrophe”: some results of integrated studies in 2011

On the basis of the analysis of published data and in the course of the authors’ long-term geochemical and acoustic surveys performed in 1995–2011 on the East Siberian shelf (ESS) and aimed to research the role of the Arctic shelf in the processes of massive methane outbursts into the Earth’s atmosphere, some crucially new results were obtained. A number of hypotheses were proposed concerning the qualitative and quantitative characterization of the scale of this phenomenon. The ESS is a powerful supplier of methane to the atmosphere owing to the continued degradation of the submarine permafrost, which causes the destruction of gas hydrates. The emission of methane in several areas of the ESS is massive to the extent that growth in the methane concentrations in the atmosphere to values capable of causing a considerable and even catastrophic warning on the Earth is possible. The seismic data were compared to those of the drilling from ice performed first by the authors in 2011 in the southeastern part of the Laptev Sea to a depth of 65 m from the ice surface. This made it possible to reveal some new factors explaining the observed massive methane bursts out of the bottom sediments.

Current rates and mechanisms of subsea permafrost degradation in the East Siberian Arctic Shelf

The rates of subsea permafrost degradation and occurrence of gas-migration pathways are key factors controlling the East Siberian Arctic Shelf (ESAS) methane (CH4) emissions, yet these factors still require assessment. It is thought that after inundation, permafrost-degradation rates would decrease over time and submerged thaw-lake taliks would freeze; therefore, no CH4 release would occur for millennia. Here we present results of the first comprehensive scientific re-drilling to show that subsea permafrost in the near-shore zone of the ESAS has a downward movement of the ice-bonded permafrost table of ∼14u2009cm year−1 over the past 31–32 years. Our data reveal polygonal thermokarst patterns on the seafloor and gas-migration associated with submerged taliks, ice scouring and pockmarks. Knowing the rate and mechanisms of subsea permafrost degradation is a prerequisite to meaningful predictions of near-future CH4 release in the Arctic.

Ionic composition of pore water in shallow shelf deposits of the Laptev Sea

The cationic and anionic compositions of pore water in shallow deposits of Buor-Khaya Bay is studied. Significant concentration heterogeneity of the vertical ionic profile in the studied drill columns is shown. It is established that the vertical ionic profile of shelf deposits of the Laptev Sea is basically formed under the influence of thawing of underwater permafrost, hydrodynamic conditions, the water mass, and heat flows and depends on the lithological and granulometric types of the deposits. The highest concentrations of ions are registered in plant detritus represented by ground grass vegetation. A relationship between the ionic composition of pore water and cryogenic state of the sequence and its variability is demonstrated using the method of major components.

Optical characteristics of the colored dissolved organic matter on the East Siberian shelf

This work is based on the results of a cruise of the R/V Akademik Lavrent’ev in September 2011 in the Laptev and East Siberian seas. The optical characteristics of one of the most characteristic components of the river runoff colored dissolved organic matter (CDOM), which intensely absorbs solar radiation in the short-wave spectrum range are analyzed. On the basis of experimental data, the possibility to use spectral characteristic not only for quantitative estimations but also for determination of the DOM composition in the waters of the East Siberian shelf is shown.

Methane in the surface waters of Northern Eurasian marginal seas

More than 12 000 measurements of the dissolved methane (CH4) concentrations in the surface waters of Northern Eurasian marginal seas (Barents, Kara, Laptev, Chukchi, and Bering Seas, Sea of Okhotsk, and Sea of Japan) during two marine expeditions (September–October 2011 and 2012) show that all seas are CH4 source to the atmosphere, but the Laptev and East Siberian seas demonstrate the strongest signal.

The first ever application of electromagnetic sounding for mapping the submarine permafrost table on the Laptev Sea shelf

The inconsistency between the position of the submarine permafrost table in the East Arctic seas revealed by simulation and anomalies in the distribution of dissolved methane associated with ascending torchlike ejections of bubbling methane made it necessary to develop a representative geophysical express method, which allows the position of the submarine permafrost table to be determined. The method is based on sounding of the generated primary electromagnetic field in the near zone of the medium and measurement of the induced secondary EM field. The reliability of the method is confirmed by core drilling in the Laptev Sea.

Peculiarities of the formation of suspended particulate matter fields in the Eastern Arctic seas

On the basis of perennial studies, the features of formations of suspended particulate matter fields were revealed depending on the evolution of synoptic processes and the river runoff. The variability in the content and distribution structure of suspended particulate matter during the ice-free period depends on variable mobilization and the contribution of terrigenous material under conditions of the Eastern Arctic periglacial lithogenesis. The northern winds and storms activate erosion of the coastal thermoabrasion benches and resuspension of sediments of the submarine coastal slope, resulting in an anomalous amount of suspended particulate matter in the coastal-shelf waters. Insignificant waves and dominant weak southern winds lead to other sedimentation conditions caused by suspended particulate matter accumulation.