A continuous 6000 year age depth relationship for the remainder of the Weißseespitze summit glacier based on ³⁹Ar and ¹⁴C dating

Abstract. Associated with ongoing global warming, prolonged periods of negative mass balance affect even Alpine glaciers in high summit regions, which are also prime candidates for paleoclimate-related ice core studies. This greatly complicates the already challenging task of establishing an age-depth relationship where now both, the age at depth and at the surface is an unknown. Radiometric ice dating methods are an important key to tackle this challenge. This study presents a comprehensive age-depth profile of the summit glacier of Weißseespitze (WSS, 3500 m a.s.l.) in the Austrian Alps, utilizing a novel combination of radiometric dating methods – ³⁹Ar and ¹⁴C. Ice cores from drilling campaigns conducted in 2019, 2023, and 2024 were analyzed to overcome challenges posed by extensive ice loss and surface melting that limit traditional dating techniques. All ³⁹Ar samples were measured using atom trap trace analysis (ATTA). Surface mass balance (SMB) data since 2019 were used to align core depths across years, and all samples were referenced to height above bedrock to standardize comparisons.

Age modeling using least squares fitting and Monte Carlo sampling was performed for three glaciological models: Nye, Raymond, and a two-parameter (2p) model to test their applicability. The 2p model provided the best fit (χ²_red = 0.4), closely matching the data and providing a continuous age-depth scale. The model yielded a mean accumulation rate of 0.53 m w.e. a^-1 (1σ range: 0.39–0.63 m w.e. a^-1) and a thinning parameter p = 0.92 (1σ: 0.81–0.97), the former agreeing with current accumulation estimates.

The results show that the surface ice dates back approximately 400 a, emphasizing the extent of recent ice loss. Apart from this, the continuous age-depth relation shows no sign of prolonged periods of mass loss at WSS within the 6000 a glaciation history prior to today.

This work underscores the utility of ³⁹Ar dating in alpine glaciology, enabling precise reconstruction of age-depth relationships even under advanced glacial retreat and enhancing our understanding of Holocene climate history in the Eastern Alps.