GEOCHEMICAL SPECIFIC OF SEDIMENTS AT METHANE COLD SEEP SITE ON THE LAPTEV SEA OUTER SHELF

Abstract

Relevance. A specific feature of the Laptev Sea shelf is the sites of discharge of methane-containing fluids from the surface of the seabed into the water column (methane cold seeps). The key biogeochemical processes occurring during methane migration through the sedimentary environment are anaerobic oxidation of methane and bacterial sulfate reduction. The activity of these processes encourages a change in the redox conditions of sedimentation, which affects the biogeochemical cycles of some redox-sensitive elements. The aim of the research is to study the influence of methane-containing fluids on the geochemical cycles of iron, carbon and some redox-sensitive elements. Objects. The data of the concentrations of carbon, iron, and some of redox-sensitive elements (Mn, Co, Ni, Cu, Zn, Cr, Ba, Mo, U) in three bottom sediment cores sampled on the outer shelf of the Laptev Sea were analyzed. Two of the three cores were obtained at methane cold seep sites and were considered as sediments subject to anaerobic methane oxidation. Methods: pyrolysis (Rock-Eval 6 Turbo, Vinci Technologies), X-Ray analysis (HORIBA X-Ray Analytical Microscope XGT 7200), Inductively coupled plasma mass spectrometry (ICP-MS, ELAN DRC-e). Results. TOC and Fe contents in sediments do not reflect the impact of anaerobic oxidation on their geochemical cycles and controlled by the specifics of the spatial distribution of sedimentary material. In all the studied cores, there are elevated Mn concentrations confined to the surface layer of sediments. At methane cold seep sites, the surface layer of bottom sediments is characterized by enrichment in Mo, Ni and Cr. The selective enrichment of the surface layer of sediments with some redox-sensitive elements can be caused by the migration of methane-containing fluids, which facilitate the transport of elements in dissolved form from deeper horizons. The sorption of these elements by organic matter and Fe-Mn oxihydroxides appears to be the key mechanism controlling the deposition of Mo, Ni, and Cr.

Keywords

• geochemistry
• methane seeps
• anaerobic methane oxidation
• laptev sea