Soils characterization at McMurdo Dry Valley (SENECA project)

The SENECA project aims to provide first evaluations of gas concentrations and emissions from permafrost and/or thawing shallow strata and to derive a first estimate of the CO2 and CH4 emission at Southern Polar Hemisphere. The obtained results can also be used to assess uncovered new problems and opportunities, such as how the Antarctica environment can increase to permanent and temporal scale the global temperatures. The project is organized in four major tasks: (1) soil gas content and origin; (2) CO2 and CH4 degassing output; (3) geophysics exploration and petrographic characterization of the soils; (4) seasonal trend of CO2 soil concentration. PETROLOGICAL DATA Soil sampling and analyses: During field activities, soil was described, and specimens were collected in such a way to obtain a homogeneous areal distribution of the samples, representative of the investigated regions. Soil sampling sites were usually coincident with soil gas measuring and collecting sites, which were located on a pre-determined grid, unless specific geomorphological units off the grid were considered of interest. Soil was described and documented at 83 locations in the Taylor Valley and 30 locations in the Lower Wright Valley. The number of soil samples collected in the Taylor and in the Lower Wright Valleys was 57 and 14, respectively. Some of the samples also included sub-samples, in order to separate the different horizons that constituted the soil. In selected sites, a sub-sample of the underlying permafrost was also collected. The number of permafrost sub-samples collected in the Taylor and in the Lower Wright Valleys was 33 and 14, respectively. Criteria for the selection of the sites where to collect permafrost thus included, in addition to the representativeness of the specific site in terms of soil textural and petrographical features, the values of soil gas measured at that site. Soil was generally constituted by lose sediments with different grain size. Locally, the upper part of the soil was weakly cemented. In these cases, an undisturbed sub-sample of the cemented soil was also collected within a rigid plastic vial. 5 sub-samples of this type were collected from the Taylor Valley and one from the Lower Wright Valley. At each considered site, the stratigraphy of the soil was described on a vertical section obtained by digging a pit down to permafrost, over an area of maximum 40x50 cm. Soil texture, grain size distribution, sedimentary structures, colour, nature of clastic elements, water content, depth and type of permafrost were described and photographically documented. Nature and dimension of gravel at the surface were also annotated. In addition, air temperature was measured using a XS Temp 7 PT 100 thermometer. Temperature was also measured at soil surface, at depth of 5 cm, 10 cm, and at every additional 10 cm depth, at the base of soil, in contact with permafrost, and within permafrost, by inserting the probe in a 5 to 10 cm deep hole made with a chisel. Weather conditions during measurements were also annotated. After measurements and sample collection, the pit was filled up again and the site recovered at our best to minimise impact. As concern the analyses, all the sampled soils have been subjected to: XRF - X-ray Fluorescence Spectroscopy ICP Ms - Inductively coupled plasma – mass spectrometry XRD - X-ray Diffraction Granulometry analysis On 20 selected samples we performed also: Gamma-ray spectrometry analysis Radon emission coefficient On permafrost sub-samples, TOC were measured On the 6 undisturbed samples, micro tomography analysis was also performed