Cryostratigraphy and Main Physical Properties of Active Layer Soils and Upper Horizon of Permafrost at the Barrow Environmental Observatory Research Site.

Abstract:

Complete understanding of the results of geophysical survey, microbiological and biogeochemical analyzes of soil cores in the Arctic environment impossible without detail description of the frozen soil and its physical properties determination. Cryostratigraphyc features i.e. total ice content and forms of ice patterns reflects the important processes such as water migration due to freezing in frozen active layer soils and history of sedimentation and freezing in underlying perennially frozen deposits. That plays significant role in biogeochemical processes that take place in the Arctic ecosystem.

Current research was based on description and analyzing of 8 cores taken during 2012 and 2013 coring campaigne had been done at the Barrow Environmental Observatory research site.

Cores were taken from different types of polygons and analyzed on lithological composition, soil density, ice content and thermal conductivity. Volumetric ice content within the active layer composed by organic soil consists of 70 to 80% and within silt one – less than 60%. Ice content of underlying syncryogenic perennial frozen deposits is about 70%. No clear evidences of soil moisture redistribution due to freezing of active layer were noticed in the cores composed by the organic soil.

Organic soil does not have any clear cryogenic structures. Ice usually fills the pores and follows the plants fibers. Mineral soil has recticulated cryogenic structure (ice forms grid like patterns with vertically oriented cells) with some thin (up to 2 cm thick) layers of soil particles and aggregates suspended in ice.

Thermal conductivity of frozen samples varies in the range from 1.5 to 2.8 W/(m*°K). It has a positive correlation with soil density and negative with gravimetric ice content (see figure below). Mineral soils have a higher bulk density and average thermal conductivity in the range 2.15 W/(m*°K), organic soils have a lower density and average thermal conductivity about 2 W/(m*°K). Samples, composed by fibrous has an extremely high ice content and low bulk density. Its average thermal conductivity is close to the values typical for ice (2.3 W/(m*°K)).

Current research was supported by US DOE as a part of research project Next Generation of Ecosystem Experiment (NGEE).