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.

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 geochemical dataset includes: 1. **Soil gas sampling/flux measurements:** Soil gas surveying involves collecting gas samples from the active layer zone to measure the concentrations of various gaseous species in the soil pores. Samples were collected by inserting a steel probe vertically into the soil to a depth ranging from 0.2 m to 0.6 m, depending on the thickness of the active layer. Soil gas samples were taken from the probe using a 60 cc plastic syringe and stored in 15 ml glass vials. The collected gas samples were analyzed with a chromatograph (CP4900 by Varian) to determine the concentrations of the following gaseous species: He, Ne, H2, O2, N2, CH4, C2H2, C2H4, C2H6, CO2, H2S. Radon (222Rn) and Thoron (220Rn) were measured directly in the field using a Durridge RAD7 instrument, performing three or four measurements with a 5-minute integration time. A total of 231 samples were collected during this expedition. Measurements of exhalation flux of CO2 and CH4 from the soil into the atmosphere were conducted using the West System (West Systems TM) accumulation static closed-chamber method. 2. **Continuous monitoring of CO2 concentrations in the active layer:** Continuous monitoring of CO2 concentrations in the bottom of the active layer was recorded. GasPro CO2 Monitoring Probes were designed to measure temperature and CO2 concentration in the unsaturated soil horizon. CO2 concentrations were measured using a Non-Dispersive Infra-Red (NDIR) sensor (model IRCA1 Alphasense). The probes collected one measurement per hour during the period 2020 - 2023 (with gaps) at strategic points within the Taylor and Wright valleys. 3. **Water samples:** We sampled shallow waters from 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 polyethylene flasks for laboratory analysis in the following quantities: - 2 flasks of 50 ml for major anions and cations - 1 flask of 50 ml for minor and trace elements - 1 flask of 100 ml for isotopic analyses - 1 serum glass bottle of 155 ml for dissolved gases in the water. Major anions and cations were sampled from filtered and acidified samples, respectively. Minor and trace elements were collected from filtered and acidified samples. An unfiltered sample was collected for the determination of stable isotope analyses (18O, D). The chemical composition analysis of dissolved gases (He, Ne, H2, O2, N2, CH4, CO2), extracted from water samples collected in serum glass bottles and sealed with gas-tight rubber plugs according to the method of Capasso and Inguaggiato (1998), was carried out in the Scott Base Laboratory using an Agilent 4900 CP Micro-gas chromatograph equipped with two TCDs and Ar as carrier gas. The 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). The analytical error was <5%. A total of 15 water samples were collected during this expedition.