DOI: 10.5285/5a286921-9031-4abc-b227-79bce58f0640
title: Geochemical data (clay mineral, XRF-scanner and biomarker data) for core LC12 sediment record from Blaso, a large, epishelf lake in NW Greenland collected July-August 2017

description: The dataset comprises multi-proxy analyses of sediment core, LC12, extracted from Blaso, a large epishelf lake on the margin of 79 degree N Ice Shelf, NW Greenland in July-August 2017. The data are used to constrain ice shelf dynamics over the last 8500 calibrated years before present (cal. years B.P., where present is A.D. 1950). A 2 m-long sediment core was recovered with a UWITEC KOL 'Kolbenlot' percussion piston corer to a total sediment depth of 5.24. Core LC12: 90 m water depth; 79.5948 ° N, 22.44233 ° E. Geochemical data for the LC12 sediment records consists of clay mineral, XRF-scanner and biomarker data. This project was funded by the Natural Environment Research Council (NERC) through Standard Grant NE/N011228/1. We thank the Alfred Wegner Institute, and particularly Angelika Humbert and Hicham Rafiq, for their significant logistic support through the iGRIFF project. Additional support was provided from Station Nord (Jorgen Skafte), Nordland Air, Air Greenland and the Joint Arctic Command. Naalakkersuisut, Government of Greenland, provided Scientific Survey (VU-00121) and Export (046/2017) licences for this work.
description: Prior to analysis sediment samples were treated with 20 % hydrogen peroxide to digest the organic material. Once the organic material has been digested the sample was centrifuged and then 20 ml distilled water plus 2 ml sodium hexametaphosphate was added to defloculate the sample. High-resolution elemental abundances were measured on the split core using a GEOTEK X-ray Fluorescence (MSCL-XRF) at 1 mm resolution. We use elemental ratios Ti/Ca as a proxy for terrigenous flux, while Mn/Fe and Br concentrations provides semi-quantitative information about lake oxygenation (Naeher et al., 2013) and marine organic carbon content (Ziegler et al., 2008) respectively. Ti contents in marine sediments is directly linked to terrigenous (siliciclastic) sediment supply delivered by fluvial and/or aeolian transport processes (Arz et al., 1999; Nace et al., 2014), while Ca concentrations reflect changes in the production of calcium carbonate (CaCO3) by marine plankton (Bahr et al., 2005). High Ti/Ca ratios are indicative of an increased terrigenous flux. The behaviour of Fe and Mn is strongly dependent on processes of oxidation and reduction. Reducing conditions are the result of O2 consumption during organic matter (OM) remineralisation, which releases Fe and Mn. Because Fe oxidises faster than Mn, high Mn accumulation and thus high(low) Mn/Fe ratios reflect oxic (anoxic) conditions. Bromine (Br) is used as a proxy for marine organic carbon, since bromine is found at higher concentrations in marine, compared to terrestrial, organic matter (Ziegler et al., 2008; Seki et al., 2019). Finally, an aliquot of the less than or equal to 2 micrometer fraction was used to determine the relative concentrations of the clay minerals smectite, illite, chlorite and kaolinite in LC12 using an automated powder diffractometer system (Rigaku MiniFlex) with CoK-alpha radiation (30 kV, 15 mA) at the Institute for Geophysics and Geology (University of Leipzig, Germany). The clay mineral identification and quantification followed standard X-ray diffraction methods (Ehrmann et al., 2011) and is used to reconstruct sediment provenance and pathways. A total of 22 sediment samples from LC12 were prepared for lipid biomarker analyses. Lipids were microwave-extracted from 0.4 to 2g of freeze-dried and homogenised sediment were extracted using dichloromethane:methanol (3:1) at an oven temperature of 70 °C for two minutes following Kornilova and Rosell-Mele (2003). Internal standards of known concentration (5-alpha-cholestane, Heptatriacontane and 2 nonadecanone) were added to aid quantification. The extracted sediment was centrifuged at 2,500rpm for 5 minutes. The solvent was decanted and then taken to near-dryness with a stream of N2. The total lipid extract was separated into 3 fractions using glass Pasteur pipettes packed with extracted cotton wool and a 4 cm silica column (high purity grade pore size 60 Angstrom 220-440 mesh particle size, 35-75 µm particle size for flash chromatography, copy right Sigma Aldrich, size of particles). Sequential elution with Hexane, Dichloromethane and Methanol (4 columns each) yielded n -alkane, ketone and polar fractions, respectively. Biomarkers were quantified and identified using gas chromatography with flame ionisation (GC-FID) and mass spectrometry (GC-MS) as outlined in detail in Sánchez-Montes et al. (2020). The internal standards were used to calculate lipid mass, normalised to the original extracted dry weight of sediment. We employ a range of n-alkanes and ketones as environmental proxies, using a series of equations used to determine the relative contribution of bacteria, phytoplankton and grasses to sediments, as well as indicators of water temperature and salinity. The terrigenous and aquatic OM equations were normalised to the weight of the sediment extracted. Also, because Blaso has experienced both marine (LF1) and lacustrine (LF2-3) conditions, the alkenone UK37 index was converted into surface water temperature (SWT) using both the surface temperature calibration equation of D'Andrea et al., (2011), which was developed for lakes in West Greenland, and the marine temperature calibration in Bendle and Rosell-Mele, (2004) developed for the Nordic Seas.
description: UWITEC KOL 'Kolbenlot' percussion piston corer GEOTEK X-ray Fluorescence (MSCL-XRF)