Branched glycerol dialkyl glycerol tetraethers (brGDGTs) of lake water filtrates from Iceland and the Eastern Canadian Arctic, 2018-2020

This dataset contains branched glycerol dialkyl glycerol tetraethers (brGDGT) distributions and total abundances for lake water filtrate samples collected from Iceland and the Eastern Canadian Arctic. Water samples were collected using a Niskin-type container from the surface, middle, and/or bottom of the lakes. Most samples were collected during the open water season. However, some samples were collected in late spring before ice out. Water was then filtered through ashed 0.3 micrometer (µm) glass fiber filters (Advantec GF-75). The filters were then freeze dried and extracted for lipid analysis. Sample collection was paired with sonde measurements of lake water temperature, pH, conductivity, and dissolved oxygen. Grab samples were additionally taken for measurements of total phosphorus, chloride, nitrate, sulfate, total organic carbon/ dissolved organic carbon (TOC/DOC), and total nitrogen. These data have been previously published (Raberg et al., 2023a; Raberg et al., 2023b). Lipid extractions were performed using one of two methods. Most samples were extracted using a modified Bligh and Dyer (BD) protocol as described in Raberg et al. (2021). Some samples were instead extracted using an accelerated solvent extractor (ASE, Dionex ASE 350) using two rounds of dichloromethane:methanol (9:1) at 100 degrees Celcius (°C) and 1500 pounds per square inch (psi). An aliquot of the total lipid extract was then filtered (0.45 µm polytetrafluoroethylene (PTFE)) and analyzed for brGDGTs using a Thermo Scientific UltiMate 3,000 high performance liquid chromatography instrument coupled with a Q Exactive Focus Orbitrap-Quadrupole high resolution mass spectrometer. Analyses were performed in full scan mode using a standard chromatographic method (Hopmans et al., 2016) with a slight modification to aid in isomer separation (Raberg et al., 2021). We used external calibrations using the C46 glycerol dialkyl glycerol tetraethers (GTGT) standard (Huguet et al., 2006) to calculate compound abundances. For a given compound, its fractional abundance was calculated as the abundance of the compound divided by the sum of all compounds (including the IIIa'' isomer).