Dissolved methane anomalies over the East – Siberian Arctic Shelf. Modeling results V.V. Malakhova, E.N. Golubeva ICMMG SB RAS, Russia, Novosibirsk Dissolved methane anomalies over the East – Siberian Arctic Shelf. Modeling results V.V. Malakhova, E.N. Golubeva ICMMG SB RAS, Russia, Novosibirsk

Motivation Motivation  Arctic Ocean is the largest pool of organic carbon (including methane and oil) in the World Ocean.  Artic Ocean is surrounded with onshore permafrost (contains ~10,000Gt C) and underlain with offshore permafrost which contains a huge reservoir of organic matter and trapped methane, including methane in form of gas hydrates.  More runoff input than any other ocean.  During the warm stages the Arctic is considered to be a source of atmospheric methane, ensuring the existence of the inter-polar CH4 gradient (8–10%); this gradient decreases to a practically negligible value during glacial epochs (IPCC, 2001).  During the warm stages the Arctic is considered to be a source of atmospheric methane, ensuring the existence of the inter-polar CH4 gradient (8–10%); this gradient decreases to a practically negligible value during glacial epochs (IPCC, 2001).

Arctic tundra is a vast and interesting ecosystem. Permafrost prevents water from draining into the soil, so that the ground is boggy in the summer. Dead plant matter covered by water can decay anaerobically to release methane

Lena river delta (NASA)

Dissolved methane in the East-Siberian Sea. Observed data Dissolved methane in the East-Siberian Sea. Observed data Distribution of dissolved methane in the surface layer (a), and bottom layer (b) (Shakhova and Semiletov, 2006). The essential increasing of the dissolved methane concentration during years. Surface layer maximum: nM, nM, nM Bottom layer: nM, nM, nM The extreme methane anomalies in plume areas indicate the presence of both surface and bottom methane sources, which might reflect unique geological, hydrological and climatic factors

Methane concentration in atmosphere surface layer  Methane in the air 2 m above the sea water along the ship route (September, 2005). (Shakhova and Semiletov, 2006).  Synchrony measurement in the subsurface ocean layer and in the atmosphere in the Eastern Siberian shelf gives that anomaly high values in air (8 ppm) is situated above the anomaly high concentrations in surface water layer (500 nMole).  Some part of these anomalies is associated with river runoff Indigirka, Kolyma, Lena  The observed methane flux to the atmosphere (Shakhova et al., 2010 )

The Siberian rivers as methane sources The Siberian rivers as methane sources The methane comes from the “tundra” soil from the wetland and the permafrost degradation. The main mechanism of the methane transport to the ocean is realized by the Arctic rivers and is dependent on the hydrological conditions. The methane comes from the “tundra” soil from the wetland and the permafrost degradation. The main mechanism of the methane transport to the ocean is realized by the Arctic rivers and is dependent on the hydrological conditions. ICMMG numerical model ICMMG numerical model By analogy with all other biogeochemical tracers, the evolution of methane concentration is modeled as advection-diffusion supplemented with local sources. By analogy with all other biogeochemical tracers, the evolution of methane concentration is modeled as advection-diffusion supplemented with local sources. Lateral boundary conditions are set according to available data about seasonal change of the Arctic rivers discharge, taken from AOMIP. Lateral boundary conditions are set according to available data about seasonal change of the Arctic rivers discharge, taken from AOMIP.

Dissolved methane in the rivers estuary.Averaged data for 2005 year Dissolved methane in the rivers estuary. Averaged data for 2005 year Ob – 7 – 41nM; Yenisei – nM; Lena – nM. “Great Siberian Rivers as sources of the methane on the Arctic shelf” Shakhova, Semiletov and Belcheva, 2007

The transport of the dissolved methane by ocean currents (1 Run)

Methane oxidation in the water Field Observations of Methane Concentrations and Oxidation Rates in the Southeastern Bering Sea (R.P. GRIFFITHS, B.A. CALDWELL, J.D. CLINE, W.A. BROICH, AND R.Y. MORITA) Methane oxidation in the water column is a microbially mediated process in which oxygen acts as the oxidant CH 4 +2O 2 =CO 2 +2H 2 O Measurements of methane oxidation rates were made in southeastern Bering Sea water Microbiological and biogeochemical Explorations in Chukchi Sea (July – August 2004) A. Savvichev

Distribution of the dissolved methane arriving into the ocean from the rivers, seasonal changes (2 Run, 2004 yr)

Distribution of the dissolved methane, seasonal changes (2 Run, continued to 2008 )

Turnover time CH4 In paper (Valentine et al., 2001) shown that the turnover time of CH4 is relatively constant (1.5 yr) in deep samples with high CH4 concentrations, but that the turnover time is much longer (decades) in shallow samples with low CH4 concentrations. In paper (Valentine et al., 2001) shown that the turnover time of CH4 is relatively constant (1.5 yr) in deep samples with high CH4 concentrations, but that the turnover time is much longer (decades) in shallow samples with low CH4 concentrations. We model lifetime and removal as: We model lifetime and removal as: - The water column deeper than 370 m - The water column shallower than 370 m

Distribution of the dissolved methane, seasonal changes (3 Run)

Conclusions Conclusions According to measurements and modeling results the Lena River runoff can give an essential income into forming of the high methane concentration in May, the further spreading occurs according to system of currents. According to measurements and modeling results the Lena River runoff can give an essential income into forming of the high methane concentration in May, the further spreading occurs according to system of currents. It is shown, that oxidation is effective control on methane concentration. Different approachers in oxidation could produce different results It is shown, that oxidation is effective control on methane concentration. Different approachers in oxidation could produce different results Thank you