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.