Leggi in italiano

View of the Commonwealth Glacier in the Taylor Valley, one of the three large McMurdo Dry Valleys in Antarctica, where the study was performed. Credit: Eli Duke/ CC BY-SA 2.0.

Many studies conducted in the North Pole region have revealed that the stability of permafrost — ground that remains at 0 °C or below for at least two years — plays an essential role in the carbon cycle, by determining how much carbon is released into the atmosphere instead of remaining trapped in the soil. However, very little is known about the release of greenhouse gases from the Antarctic permafrost. A team led by Livio Ruggiero and Alessandra Sciarra, from Italy’s Institute for Geophysics and Volcanology, decided to investigate.

In the southern hemisphere, permafrost soils are found at high elevations in the Sub-Antarctic islands, in the Antarctic Peninsula, and in the ice-free areas of the Antarctic continent. “The majority of previous studies focused on the Antarctic peninsula, but very few were done on the continent,” says Sciarra. During the Austral summer 2019–2020, the team measured the concentrations of soil gases (including carbon dioxide, methane, helium and hydrogen) and the flux of CO2 at the interface between the permafrost and the soil layer above it, called the active layer, over an area of more than 20 km2. The area is in the Taylor Valley, the southernmost of the three large McMurdo Dry Valleys in the Transantarctic Mountains, the largest ice-free region in Antarctica.

The team investigated potential leakages from the permafrost, discovering concentrations of different anomalous gases and CO2 fluxes at the surface above what would be expected because of the ‘normal’ soil respiration caused by microbial activity1. They found concentrations of up to 3.4% of carbon dioxide together with significant concentrations of methane, helium at the base of the active layer, and used statistical methods to estimate CO2 emissions of 15 tonnes per day from the area, which is 1 or 2 orders of magnitude higher than the values found by the few previous studies.

The scientists are still unsure about the mechanisms responsible for this gas release. Permafrost is generally a barrier to the movement and escape of gases, but underground faults and fractures can lead to surface gas anomalies with higher concentrations than deeper ones. Measuring gas emissions from the soil can create a map of such faults and fractures, and this is the first time that this method has been applied in Antarctica, in particular, it is the first time that scientists measure the distribution of gases over a large area rather than at a specific point and time. “The more you have a homogeneous spatial distribution and the larger the area covered, the more it is possible to understand if there is degassing or not, where the gas is released and whether there is a linked presence of faults,” adds Sciarra.

This work has produced a map of CO2 emissions which may serve as a starting point for re-search aimed at evaluating the origin of these gases and monitoring the greenhouse gas emissions released by the Antarctic permafrost, to understand how they are both contributing to global warming and being affected by it.