A core of ice from the center of the lake was obtained in March 2023 using a Kovacs Mark V coring system. The core barrel extracts a 14 cm diameter ice core and returned a ~40 cm-long ice core topped with ~5 cm of snow cover. This core was transported back to the field station in a clean plastic bag. Visual examination of the core revealed the presence of 3 layers: a ~5 cm unconsolidated snow layer at the top; a ~20 cm opaque layer identified as deriving from snow and referred to hereafter as 'snow ice'; and a ~20 cm transparent layer identified as frozen lake water or 'lake ice'. The outer layer of the ice core was washed liberally with methanol and Milli-Q water prior to sampling, and all samples from the ice core specifically avoided the outer surface of the core that was in direct contact with the coring system. Five discrete sample layers, one from the unconsolidated snow and two each from the snow ice and lake ice, were collected from this core by manual separation with a ceramic chisel. These approximately 400 mL samples were melted in acid-cleaned 500 mL Savillex Teflon reactors prior to transportation back to Woods Hole Oceanographic Institution (WHOI). Elemental compositions were determined using a Thermo Fisher iCAP-Q inductively coupled plasma mass spectrometer (ICP-MS) at the WHOI Plasma Facility following 200 dilution of a 10 μL aliquot in 2 % HNO3. Indium (In) was added to samples at a concentration of 1 ng/g prior to analyses to monitor and correct for instrument drift by normalizing to In intensities. Concentrations were calculated using a five-point calibration curve obtained by fitting of ion beam intensities measured for serial dilutions of a gravimetrically prepared multi-element standard. The relative standard deviation (RSD) for five measurements of each sample was ~10% on the iCAP-Q. The accuracy and precision of similar concentration measurements on iCAP-Q at WHOI have previously been determined to be ± 5-10 % (1SD) based on comparison with USGS reference materials AGV-1, AGV-2, BHVO-1, BHVO-2, BIR-1, and BCR-2 prepared and analyzed as unknowns during earlier runs (Jochum et al., 2016; Shu et al., 2017).
