Cryogenic cave minerals recorded the 1889CE melt event in northeastern Greenland

The investigation of cryogenic cave minerals (CCMs) has developed in recent decades to be a particularly valuable proxy for palaeo-permafrost reconstruction. Due to difficulties, however, in obtaining reliable chronologies with the so-called "fine" form of these minerals, such studies have thus far utilised the "coarse" form. In this study, we successfully investigate the northernmost-known deposit of fine-grained CCMs, which are situated in Cove Cave (Greenlandic translation: Eqik Qaarusussuaq), a low-elevation permafrost cave in northeastern Greenland (80 degrees N). The Cove Cave CCMs display a complex mineralogy that consists of fine-grained cryogenic cave carbonates and sulfate minerals (gypsum, eugsterite, mirabilite, and loweite). Until now, previous attempts to date fine-grained CCMs have been unsuccessful; however, here we demonstrate that precise dating is possible with both isochron-based Th-230 / U dating and C-14 dating if the dead carbon fraction is reliably known. The dating result (65 +/- 17 a BP; 1885 +/- 17 CE) shows that the Cove Cave CCMs formed during the late Little Ice Age, a time interval characterised by cold temperatures and abundant permafrost in northeastern Greenland, making water infiltration into Cove Cave dependent on the water amount and latent heat. We relate the CCM formation to a combination of black carbon deposition and anomalously high temperatures, which led to widespread melting over large areas of the Greenland ice sheet in the course of a few days. We propose that the anomalous weather conditions of 1889 CE also affected northeastern Greenland, where the enhanced melting of a local ice cap resulted in water entering the cave and rapidly freezing. While calcite and gypsum likely precipitated concurrently with freezing, the origin of the other sulfate minerals might not be purely cryogenic but could be linked to the subsequent sublimation of this ice accumulation in a very dry cave environment.