University of Otago
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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) CO 2 and CH 4 degassing output; (3) geophysics exploration and petrographic characterization of the soils; (4) seasonal trend of CO2 soil concentration. Geoelectrical data: The field campaign took place in the Taylor Valley, which is part of the McMurdo Dry Valleys (Antarctica). We performed 2D data acquisition on five profiles, ~N-S and ~W-E trending from Dec 26, 2019 to Jan 20, 2020. We used the Fullwaver system (Gance et al., 2018, Lajaunie et al.,2018). The Fullwaver system does not require long and heavy multi-core cables and fixed array configurations. Recording and injection devices come into separate hardware. Specifically, this field apparatus consists in: a) an induced polarization transmitter (VIP) b) one current measurement unit called I-Fullwaver c) a set of 2-channels independent receiving nodes called V-Fullwavers d) a motor-generator Current is injected through an induced polarization transmitter, (VIP 5000, IRIS Instruments). This transmitter enables to inject current up to 10 Amps, 5000W and 3000V, with a frequency of 0.5Hz. An external 7kVA generator provides current for the VIP. The receiving nodes record continuously the electrical field and the injection electrodes can be moved inside and outside the receiving nodes with any type of electrode array configuration. Injected current is recorded in real-time on the I-Fullwaver. Profile 1 (4.5 km length), 2 (3.8 km length) and 3 (3.2 km length) were designed in order to reach an ideal depth of investigation of ~800 m, while profiles 4 (1.8 km length) and 5 (1.6 km length) were designed in order to reach the depth of the borehole data from DVDP 11 (~300m), giving an independent geological control in phase of modeling and interpretation. We used from 8 to 12 receiving nodes combined with one injection node. Each V-Fullwaver was connected to 3 receiving electrodes deployed in a line (P1, P2, P3). Their spacing was set to 50 meters. Between each receiving node a 100 m spacing was set. One electrode A (e.g. Tx 1 ) was always fixed at one end of the profile and we moved the B (e.g. Tx 4 ) electrode across the acquisition line, until completing the largest injection, e.g. Tx1 -Tx9 . This procedure was repeated forward and backward, adopting Tx 1 or the last transmission as fixed electrode respectively. The distance between the injections was set to 200m for the transmissions located inside or immediately close to the V-Fullwaver line, while for the injections external to the V-Fullwaver line, the distance was set to 250m (e.g. for profiles 1, 2, 3). Receiving and injecting nodes are GPS-synchronized with an independent GPS unit mounted on each Fullwaver. Post-processing of the raw data can be performed to improve the signal to noise ratio producing high-resolution data. GPS positions for all the electrodes were acquired with a GPSMAP 64s, with an accuracy of ~3 m. For the data processing, we will utilize data of the surface topography extracted from Lidar of the Taylor Valley (Fountain et al., 2017). During the acquisition, contact resistances ranged from ~0.6 KOhm to 2.3 KOhm. We injected from 0.8 A to 2.5 A for 120 to 180s, in order to obtain as many stacks as possible to decrease the signal to noise ratio.
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
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. Geochemical data: The geochemical dataset includes: Soil gas sampling/flux measurements and GasPRO CO2 monitoring probes Soil gas surveying consists in collecting gas samples from the active layer zone to measure the concentrations of some gaseous species in the soil pores. To avoid the major influence of meteorological variables, samples are collected inserting a steel probe vertically in the soil to a depth from 0.2 m to 0.6 m, depending by the thickness of the active layer. Soil gas samples are taken from the probe by using a 60 cc plastic syringe and stored in a 15 ml glass vials. The collected gas samples have been analyzed in Scott Base lab with a chromatographer (CP 4900 by Varian) to define the concentrations of the following gaseous species: He, Ne, H2, O2, N2, CH4, C2H2, C2H4, C2H6, CO2, H2S. Radon (222Rn) and Thoron (220Rn) have been measured directly in the field using Durridge RAD7 instrument performing three/four measurements with 5-minute integration time. A total number of 226 samples were collected in this first expedition. Measurements of exhalation flux of CO2 and CH4 from the soil into the atmosphere have been conducted using the West System (West Systems TM) accumulation static closed-chamber method. Continuous monitoring of CO2 concentrations in active layer bottom was started with the deployment of GasPro CO2 Monitoring Probe designed to measure temperature, pressure and CO2 concentration in the unsaturated soil horizon. CO2 concentration is measured via a Non-Dispersive Infra-Red (NDIR) sensor (model IRC‐A1 Alphasense). The probes are equipped with four batteries and a small solar panel that should last for 10 to 12 months (depending on the outside temperature), collecting 1 measurement/hour. Water and permafrost sampling We sampled shallow waters among all streams, ponds and lakes in the studied areas. Physical-chemical parameters such as water temperature, pH, redox potential (Eh), electrical conductivity and alkalinity were determined in situ. Water samples were collected and stored in high-density polyethene flacons for laboratory analysis in the following amount: 2 flacons of 50ml for major anions and cations 1 flacon of 50ml for minor and trace elements 1 flacon of 100ml for isotopic analyses 1 serum glass bottle of 155ml for dissolved gas in the water. Major anions and cations were sampled on filtered and filtered and acidified samples, respectively. Minor and trace elements were collected on filtered and acidified samples. An unfiltered sample was collected for the determination of stable isotope analyses (δ18O, δD). The analysis of the chemical composition of dissolved gases (He, Ne, H2, O2, N2, CH4, CO2), extracted from water samples collected in serum glass bottles and sealed by gas-tight rubber plugs according to the method of Capasso and Inguaggiato (1998), was carried out in the Scott Base Laboratory by using a Agilent 4900 CP Micro-gas chromatograph equipped with two TCDs and Ar as carrier gas. Dissolved gas composition (expressed in mmol/L at STP) was calculated from the composition of the exsolved gas phase based on the solubility coefficient of each gas compound (Whitfield, 1978). Analytical error was <5%. A total number of 31 water samples were collected in this expedition. In addition, 33 permafrost samples were collected. These samples were sampled by hitting the permafrost with a hammer and chisel and collecting the small pieces of still frozen permafrost in a serum glass bottles of 155 ml. The bottle was sealed and vacuum-packed by removing the air inside it using a needle and syringe. Once the permafrost samples were defrosted, the gas content in the bottles were measured (He, Ne, H2, O2, N2, CH4, CO2). These measurements were performed directly at Scott Base using the Agilent 4900 CP Micro-gas chromatograph.