The Impact of Methane Seepage on the Pore-Water Geochemistry across the East Siberian Arctic Shelf

Natalia Guseva,Elena Gershelis,Elena Gershelis,Yulia Moiseeva,Igor Semiletov,Evgeniy Yakushev,Darya Purgina,Darya Purgina

doi:10.3390/w13040397

Abstract

East Siberian Arctic Shelf, the widest and the shallowest shelf of the World Ocean, covering greater than two million square kilometers, has recently been shown to be a significant modern source of atmospheric methane (CH4). The CH4 emitted to the water column could result from modern methanogenesis processes and/or could originate from seabed deposits (pre-formed CH4 preserved as free gas and/or gas hydrates). This paper focuses primarily on understanding the source and transformation of geofluid in the methane seepage areas using ions/trace elements and element ratios in the sediment pore-water. Six piston cores and totally 42 pore-water samples were collected in the East Siberian Sea and the Laptev Sea at water depths ranging from 22 to 68 m. In the active zones of methane release, concentrations of vanadium, thorium, phosphorus, aluminum are increased, while concentrations of cobalt, iron, manganese, uranium, molybdenum, copper are generally low. The behavior of these elements is determined by biogeochemical processes occurring in the pore-waters at the methane seeps sites (sulfate reduction, anaerobic oxidation of methane, secondary precipitation of carbonates and sulfides). These processes affect the geochemical environment and, consequently, the species of these elements within the pore-waters and the processes of their redistribution in the corresponding water–rock system.

Highlights

The most significant warming is manifested in the high latitudes of the northern hemisphere
The CH4 emitted from the seafloor to the water column could result from modern methanogenesis processes and/or could originate from seabed deposits [5]
The main purpose of this study is the identification of the pore-water geochemical indicators in the methane seepage areas

Summary

Introduction

The most significant warming (the so-called “Arctic amplification”) is manifested in the high latitudes of the northern hemisphere. Arctic warming drastically accelerates the thaw-release of permafrost carbon, and this process could produce strong positive feedback to the ongoing climate warming. The Arctic Seabed is thought to store significant amounts of permafrost organic carbon and methane (CH4 ) including permafrost-associated and continental slope CH4 hydrates [1,2,3]. The CH4 emitted from the seafloor to the water column could result from modern methanogenesis processes and/or could originate from seabed deposits (pre-formed CH4 preserved as free gas and/or gas hydrates) [5]. The CH4 entering the surface sediments activates many sediment–water exchange processes, and affects the biogeochemical responses of the pore-water (seawater trapped in the pores of the sediments). Major and trace elements, as well as rare earth elements (REEs), are often employed as geochemistry indicators for these processes.

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