ALBERT

Description: Oxygen isotopes in biogenic silica (δ18O BSi) from lake sediments allow for quantitative reconstruction of past hydroclimate and proxy–model comparison in terrestrial environments. The signals of individual records have been attributed to different factors, such as air temperature (T air ), atmospheric circulation patterns, hydrological changes and lake evaporation. Here, we provide 55 composite down–core records published to date and complemented with additional lake basin parameters (e.g. lake water residence time and catchment size) to best characterize the signal properties. Records feature widely different temporal coverage and resolution ranging from decadal–scale records covering the last 150 years to records with multi–millennial scale resolution spanning glacial–interglacial cycles. Best coverage in number of records (N=37) and datapoints (N=2112) is available for northern hemispheric (NH) extra–tropic regions throughout the Holocene (corresponding to Marine Isotope Stage 1; MIS 1).

Description: Lake sediment samples were taken in April 2013 from the ice by drilling through lake ice and recovering an undisturbed core using a HON-Kajak sediment corer. Samples were analysed for pigments (University of Nottingham), carbon isotopes and C/N ratios (BGS, Keyworth), lipid biomarkers (Newcastle University) and compound-specific carbon isotopes (CUG, Wuhan). The purpose of the analyses was to develop an environmental reconstruction of carbon cycling for an upland lake (named Disko 2) to encompass the Little Ice Age to recent warming climate periods. Analyses were completed as part of Mark A. Stevenson's PhD research while based at the University of Nottingham, UK (Stevenson, 2017, http://eprints.nottingham.ac.uk/46579). ²¹⁰Pb, ²²⁶Ra, ¹³⁷Cs and ²⁴¹Am concentrations were measured by direct gamma assay in the Environmental Radiometric Facility at University College London (Dr Handong Yang), using an ORTEC HPGe GWL series well-type coaxial low background intrinsic germanium detector. Radiometric dating techniques follow Appleby et al, 1986 (doi: 10.1007/BF00026640), Appleby et al, 1992 (doi:10.1016/0168-583X(92)95328-O) and Appleby, 2001 (doi:10.1007/0-306-47669-X_9) with core extrapolation and linear interpolation used to derive an age depth model to the base of the core. The pigment β-carotene was analysed on an Agilent 1200 series high-performance liquid chromatography (HPLC) using separation conditions outlined in McGowan et al., 2012 (doi:10.1111/j.1365-2427.2011.02689.x). Bulk δ¹³C and C~org~/N ratios were analysed on acidified samples using a Costech ECS4010 elemental analyser (EA) coupled to a VG Triple Trap and a VG Optima dual-inlet mass spectrometer. Key lipid biomarkers (n-alkanes, n-alkanoic acids (as fatty acid methyl esters (FAMEs), n-alkanols and sterols) were analysed using an Agilent 7890A GC coupled to a 5975C MS according to Pearson et al., 2007 (doi:10.1016/j.orggeochem.2007.02.007) and are expressed as ratios, relative to the total of each compound class. Specific ratios were also calculated for CPI 2 n-alkanes (Marzi et al., 1993; doi:10.1016/0146-6380(93)90016-5), terrestrial aquatic ratio (TAR) for n-alkanes (Bourbonniere and Meyers, 1996; doi:10.1007/s002540050074), index of waxy n-alkanes to total hydrocarbons (PWAX) (Zheng et al., 2007; doi:10.1016/j.orggeochem.2007.06.012) and carbon preference index (CPI) for n-alkanoic acids (Matsuda and Koyama, 1977) (doi:10.1016/0016-7037(77)90214-9). Compound-specific δ¹³C on C~28:0~ fatty acid methyl ester (FAME) was analysed using a Thermo Finnigan Trace GC coupled to a Thermo Finnigan Delta Plus XP isotope ratio mass spectrometer using a combustion interface (GC-C-IRMS) according to conditions in Huang et al. (2018; doi:10.1038/s41467-018-03804-w). Acknowledgements: Mark Stevenson gratefully acknowledges the receipt of a NERC/ESRC studentship (ES/J500100/1). We acknowledge grants IP-1393-1113 & IP-1516-1114 from the NERC Isotope Geosciences laboratory (NIGL) for the analysis of δ¹³C~org~ & C/N ratios on sediment, soil and plant samples. Lipid and water chemistry analyses were funded by the Freshwater Biological Association's 2015 Gilson Le Cren Memorial Award to Mark Stevenson. We thank Teresa Needham, Christopher Kendrick, Julie Swales, Ian Conway, Graham Morris, Bernard Bowler, Paul Donohoe, Qingwei Song and Jiantao Xue for technical support. We acknowledge the support of Handong Yang for radiometric dating. Financial support for fieldwork was awarded via the INTERACT transnational access scheme (grant agreement No 262693) under the European Community's Seventh Framework Programme and UK RI NERC grant NE/K000276/1. Logistical support is acknowledged from University of Copenhagen Arktisk Station including Ole Stecher, Kjeld Mølgaard and Erik Wille.