Radon isotopes as tracers of climate-sensitive subsurface connectivity in Antarctic permafrost

Assessing how permafrost controls subsurface gas transfer is difficult in polar deserts, where direct observations of thaw state and permeability are logistically limited. Here we test whether paired soil-gas measurements of radon (222Rn) and thoron (220Rn) can allow distinguishing shallow active-layer production from deeper advective gas transport in Taylor Valley, Antarctica. We carried out a systematic grid survey at 149 sites during two austral summers (2019/20 and 2023) and combined field measurements with laboratory determinations of radionuclide content and radon/thoron exhalation from active-layer sediments. The two isotopes behaved differently. 220Rn, which decays very rapidly, was consistent with a dominantly shallow source, although field values were systematically lowered by sampling dilution. By contrast, 222Rn did not scale with shallow production alone, and the highest field concentrations exceeded the locally constrained equilibrium range expected from the active layer. This indicates an additional transport component, most plausibly linked to upward gas migration from below the active layer. The strongest 222Rn anomalies were more widespread in 2019/20 compared with the colder 2023 campaign, suggesting that short-term meteorological conditions can modulate subsurface connectivity and gas transport efficiency. These results show that radon isotopes provide a practical framework for identifying shallow versus deeper gas pathways and for monitoring climate-sensitive changes in Antarctic permafrost systems.