Preservation of Glaciochemical Signals in a Warming Tropical Ice Cap: Evidence from the 2022 Quelccaya Ice Core

Abstract. Paleoclimate records stored in ice cores are facing great threat as on-going mass loss is rapidly accelerating. To study Amazon’s paleoclimate, an ice core was drilled in the Quelccaya ice cap, in Peru, in 2022. However, as a first step, post-depositional alterations need to be discussed and described. During drilling, one water table (WT) associated with the firn-ice transition and a major fracture at 45 m depth were identified. Here we present the first chemical results retrieved from the ice core and discuss the preservation state of the record in terms of post-depositional alterations. Concentrations of levoglucosan, Na⁺, K⁺, Cl⁻, SO₄²⁻ and NO₃⁻ were analyzed and compared with the relatively insoluble and immobile black carbon signal. Furthermore, signal preservation was evaluated using descriptive statistics, covariance analysis, ionic balance, and multivariate classification. Statistical analyses reveal enhanced ion concentration atop the WT. The section below the WT extending to the fracture is marked by a highly altered chemical signal, as indicated by multivariate analysis. Within this interval, Cl⁻ is strongly depleted and Na⁺ shows increased association with SO₄²⁻ and NO₃⁻, while the ionic balance indicates increased acidity relative to the WT onset. Below the fracture, chemical signals are attenuated but largely preserved. Principal Component Analysis coupled to Fuzzy C-Means clustering independently identifies the WT, altered ice interval, the fracture zone and a deep ice anomaly, suggesting variable preservation along the core. We define depth intervals characterized by preserved, amplified, altered and attenuated signals and show that despite significant meltwater influence, post-depositional alterations are locally concentrated rather than affecting the entire record. These results provide a basis for future paleoclimatic investigations using what could be the last Quelccaya Ice Cap ice core before continued melting irreversibly alters the record.