DOI: 10.18739/a27p8tf8w
title: Soil branched Glycerol dialkyl glycerol tetraether (brGDGT) distributions, soil temperatures, soil properties, and air temperatures of the Eastern Canadian Arctic and Iceland,2023-2024

description: This dataset consists of lipid biomarker (branched glycerol dialkyl glycerol tetraether (brGDGT)) data, soil properties (pH, electrical conductivity, and soil water content), soil temperature data, and air temperature data for surface soils collected from the Eastern Canadian Arctic (ECA) and Iceland. These data were supplemented with brGDGT, soil property, soil temperature, and air temperature data from previously published studies from Iceland (De Jonge et al., 2019), China (Wang et al., 2020; Wang and Liu, 2021), Colombia (Pérez-Angel et al., 2020), and Scandinavia (Halffman et al., 2022).
 We collected soil samples at 0-10 centimeter (cm) depth from the Eastern Canadian Arctic (ECA; n = 44) and Iceland (n = 24) in the summers of 2015-2019. For 27 soil sites in the ECA and all soil sites in Iceland, we deployed in situ soil temperature loggers (Thermochron DS1925L or DS1922L iButtons, Maxim Integrated Products) at 10 cm depth for 1 to 2 years (362 – 727 days). All loggers had a 1- to 3-hourly sampling interval except for four deployed at sites CF3 and CF8 in the ECA, which had a 6-hour sampling interval. Raw soil temperature data is available at (Raberg, de Wet, et al., 2022; Raberg, Harning, Geirsdóttir, et al., 2021).
 We measured the pH of all ECA and Iceland soils using an Oaktan pH 150 meter with a WD‐35614‐30 probe. Soil pH was measured using milli‐Q water in a 1:2.5 (w:w) soil:water ratio. New containers were used for each soil and the pH meter was calibrated using pH 4.00, 7.00, and 10.00 buffer solutions every 5-10 samples. Electrical conductivity was measured with a SevenEasy conductivity meter (Mettler Toledo) at a 1:5 (w:w) soil:water ratio, with a calibration solution checked every 15-20 samples. SWC, calculated as the percent of the sample mass that was lost after freeze drying (SWC = (mass wet soil - mass dry soil) / mass dry soil × 100), was measured for all soils from Iceland and 15 soils from the ECA.
 For brGDGT analysis, we extracted 1-10 g of freeze-dried soil using a modified Bligh and Dyer method (Bligh and Dyer, 1959; Raberg, Flores, et al., 2022; Wörmer et al., 2013). We analyzed brGDGTs using a Thermo Scientific UltiMate 3,000 high-performance liquid chromatography instrument coupled to a Q Exactive Focus Orbitrap-Quadrupole high-resolution mass spectrometer (HPLC-MS) in full scan mode. We used a slightly modified version (Raberg, Harning, Crump, et al., 2021) of the chromatographic methods established by Hopmans et al. (2016), and identified brGDGTs based on their characteristic masses and elution patterns. We added a known quantity (1μg) of C46 GDGT internal standard (Huguet et al., 2006) to the extracts quantify brGDGT yields. BrGDGTs are reported as fractional abundances within the pool of the 15 most commonly measured brGDGTs. We also report fractional abundances of brGDGTs within an extended pool, which includes both the 15 commonly measured brGDGTs and less commonly reported isomers (IIIa’’ and 7-methyl isomers). Finally, we report the presence or absences of overly branched GDGT with a mass-to-charge ratio of 1064.
 To supplement the ECA and Iceland datasets, we also compiled results from published studies containing soil brGDGTs with associated in situ soil temperatures. These include 37 soils from altitudinal transects in Scandinavia (Halffman et al., 2022), 30 soils from geothermal transects in Iceland (De Jonge et al., 2019; Sigurdsson et al., 2016), 12 soils from an altitudinal transect in China (Mt. Laji; Wang and Liu, 2021), 30 soils from an altitudinal transect in the tropical Andes of Colombia (Pérez-Angel et al., 2020), and 149 soils from a regional study in China (Wang et al., 2020). Where data were available (n = 97), monthly mean soil temperatures were calculated from hourly data that was either previously published (Halamka et al., 2022; Halffman et al., 2022; Sigurdsson et al., 2016) or provided through personal communication with the authors (L. Pérez-Angel; C. de Jonge). Monthly, seasonal, or annual soil temperatures for the remaining samples were compiled as available from published studies and through personal communication with the authors (H. Wang and W. Liu). We calculated 10 soil temperature parameters (e.g., mean summer soil temperature), which are defined in the “readme” tab of the dataset.
 Finally, we generated monthly air temperatures for all ECA and Icelandic sites in this study following the methods of Raberg et al. (2021). Briefly, for soils from six lakes in the ECA (Birch (BIR), Brother-of-Fog (BRO), Qaupat (QPT), Clyde Forelands 8 (CF8), Arnuiq (ARQ), and South America Lake (SAL)), we used a transfer function to convert 2 m air temperatures recorded by iButton temperature loggers to 30-year climate normals (1971-2000) using data from nearby meteorological stations (Department of Environment, Government of Canada). For all other samples, we used the WorldClim database (Fick and Hijmans, 2017) to generate 30-year (1970-2000) air temperature climate normals. For each soil temperature parameter above, we calculated an analogous air temperature parameter (e.g., mean annual air temperature (MAAT)), which are also defined in the “readme” tab of the dataset.
 Bligh, E. G., and Dyer, W. J. (1959). A rapid method of total lipid extraction and purification. Canadian Journal of Biochemistry and Physiology, 37(8), 911–917. https://doi.org/10.1139/o59-099
 Halamka, T. A., Raberg, J. H., McFarlin, J. M., Younkin, A. D., Mulligan, C., Liu, X.-L., et al. (2022). Production of diverse brGDGTs by Acidobacterium Solibacter usitatus in response to temperature, pH, and O2 provides a culturing perspective on brGDGT proxies and biosynthesis. Geobiology, 00, 1–17. https://doi.org/10.1111/GBI.12525
 Halffman, R., Lembrechts, J., Radujković, D., De Gruyter, J., Nijs, I., and De Jonge, C. (2022). Soil chemistry, temperature and bacterial community composition drive brGDGT distributions along a subarctic elevation gradient. Organic Geochemistry, 163, 104346. https://doi.org/10.1016/j.orggeochem.2021.104346
 Hopmans, E. C., Schouten, S., and Sinninghe, J. S. (2016). The effect of improved chromatography on GDGT-based palaeoproxies. Organic Geochemistry, 93, 1–6. https://doi.org/10.1016/j.orggeochem.2015.12.006
 Huguet, C., Hopmans, E. C., Febo-Ayala, W., Thompson, D. H., Sinninghe Damsté, J. S., and Schouten, S. (2006). An improved method to determine the absolute abundance of glycerol dibiphytanyl glycerol tetraether lipids. Organic Geochemistry, 37(9), 1036–1041. https://doi.org/10.1016/j.orggeochem.2006.05.008
 De Jonge, C., Radujković, D., Sigurdsson, B. D., Weedon, J. T., Janssens, I., and Peterse, F. (2019). Lipid biomarker temperature proxy responds to abrupt shift in the bacterial community composition in geothermally heated soils. Organic Geochemistry, 137. https://doi.org/10.1016/j.orggeochem.2019.07.006
 Pérez-Angel, L. C., Sepúlveda, J., Molnar, P., Montes, C., Rajagopalan, B., Snell, K., et al. (2020). Soil and Air Temperature Calibrations Using Branched GDGTs for the Tropical Andes of Colombia: Toward a Pan-Tropical Calibration. Geochemistry, Geophysics, Geosystems, 21(8), 1–18. https://doi.org/10.1029/2020GC008941
 Raberg, J. H., Harning, D. J., Crump, S. E., De Wet, G., Blumm, A., Kopf, S., et al. (2021). Revised fractional abundances and warm-season temperatures substantially improve brGDGT calibrations in lake sediments. Biogeosciences, 18, 3579–3603. https://doi.org/10.5194/bg-18-3579-2021
 Raberg, J. H., Harning, D. J., Geirsdóttir, Á., Sepúlveda, J., and Miller, G. H. (2021). Soil and lake water temperatures of Iceland (2019-2021). Arctic Data Center.
 Raberg, J. H., de Wet, G., Crump, S. E., Raynolds, M. K., Sepúlveda, J., and Miller, G. H. (2022). Air, soil, and lake water temperatures of the Eastern Canadian Arctic (2017-2021). Arctic Data Center.
 Raberg, J. H., Flores, E., Crump, S. E., Wet, G. de, Dildar, N., Miller, G. H., et al. (2022). Intact Polar brGDGTs in Arctic Lake Catchments: Implications for Lipid Sources and Paleoclimate Applications. Journal of Geophysical Research: Biogeosciences, 127(10), e2022JG006969. https://doi.org/10.1029/2022JG006969
 Sigurdsson, B. D., Leblans, N. I. W., Dauwe, S., Gudmundsdóttir, E., Gundersen, P., Gunnarsdóttir, G. E., et al. (2016). Geothermal ecosystems as natural climate change experiments: The ForHot research site in Iceland as a case study. Icelandic Agricultural Sciences, 29(1), 53–71. https://doi.org/10.16886/IAS.2016.05
 Wang, H., and Liu, W. (2021). Soil temperature and brGDGTs along an elevation gradient on the northeastern Tibetan Plateau: A test of soil brGDGTs as a proxy for paleoelevation. Chemical Geology, 566, 120079. https://doi.org/10.1016/j.chemgeo.2021.120079
 Wang, H., An, Z., Lu, H., Zhao, Z., and Liu, W. (2020). Calibrating bacterial tetraether distributions towards in situ soil temperature and application to a loess-paleosol sequence. Quaternary Science Reviews, 231, 106172. https://doi.org/10.1016/j.quascirev.2020.106172
 Wörmer, L., Lipp, J. S., Schröder, J. M., and Hinrichs, K. U. (2013). Application of two new LC-ESI-MS methods for improved detection of intact polar lipids (IPLs) in environmental samples. Organic Geochemistry, 59, 10–21. https://doi.org/10.1016/j.orggeochem.2013.03.004