Active Layer Monitoring on James Ross Island, Antarctica: Results from 2006–2023

The northern part of James Ross Island, Ulu Peninsula, is one of the largest ice-free areas in Antarctica. Its diverse local conditions, including variations in altitude, lithology, topography, and vegetation cover, create unique opportunities for active layer research. Monitoring of active layer temperature and thickness on the Ulu Peninsula began in 2006, with the installation of soil temperature measurement profiles at two initial sites. Over time, the network expanded to 12 locations, comprising more than 20 profiles that measure soil temperatures from the surface layer (5 cm depth) down to the upper permafrost boundary (75–200 cm). These sites were strategically selected to represent different lithological and altitudinal conditions. In 2014, the first Circumpolar Active Layer Monitoring South (CALM-S) site was established near the Johann Gregor Mendel Station, with two additional CALM-S sites added in 2017.

Long-term data from Abernethy Flats (45 m a.s.l.) showed mean annual ground temperatures (MAGT) ranging from –5.7 °C at 5 cm depth to –6.0 °C at 50 cm depth during 2006–2023. Ground temperatures at other sites varied by approximately +0.5 °C to –2.0 °C compared to Abernethy Flats. Over the study period, significant cooling (approximately –1.0 °C per decade) was observed until 2013–2015, followed by a warming trend, culminating in 2023 as the warmest year recorded on James Ross Island. Active layer thickness showed high variability, largely influenced by lithology, with typical values ranging from 50 to 90 cm. Maximum thicknesses exceeding 130 cm were recorded at the CALM-S JGM site. Similar to temperature trends, the active layer thinned until 2013 (approximately 10–15 cm per decade) and then thickened at a comparable rate thereafter.