DOI: 10.5285/c75ea98b-080e-455e-a54f-a9e8cf07aa73
title: Biological, chronological, geochemical and physical sedimentological data for the LP08 lake sediment record extracted from Lago Pato, Torres del Paine, Chile in 2007-2008

description: The dataset comprises of site data and multiproxy analyses of LP08 lake sediment cores extracted from Lago Pato, a small lake basin at -51.3003, -72.6786 and approx 33 m a.s.l., which is topographically separated from Lago del Toro in Torres del Paine (TdP). The data are used to constrain glacier dynamics and lake level change in the TdP and Ultima Esperanza region over the last approx 30,000 cal a BP (30 ka). Data for the LP08 sediment record consist of downcore measurements of biology, chronology, geochemistry, sedimentology proxy data collected from the current depocentre between November 2007 to March 2008. This project was funded by the Natural Environment Research Council (NERC) through the British Antarctic Survey (BAS) and an UGent BOF bilateral collaboration project. RMcC was supported by Programa Regional R17A10002 and R20F0002 (PATSER) ANID. We gratefully acknowledge the University of Magallanes (UMAG) and the University of Santiago (Carolina Diaz) for assistance with fieldwork; the NERC/SUERC AMS Radiocarbon Facility for providing initial range-finder radiocarbon dates; the NERC Isotope Geosciences Laboratory (NIGL, now National Environmental Isotope Facility, NEIF, at the British Geological Survey) and Melanie Lang for stable carbon isotope analysis; Aberystwyth University (David Kelly), Durham University (Neil Tunstall and Christopher Longley) and Edinburgh University (Chris Hayward) for use of their core scanning and microprobe facilities and technical support.
description: Sediment cores were collected using a UWITEC-gravity corer, Livingston piston corer from the deepest point (approx 3.5 m of water depth) in Lago Pato (LP08: 51.3003 S, 72.6786 W, 32 m a.s.l., 600 cm total recovered sediment depth). Biology Subsamples for diatom and stomatocyst analysis were taken at 4 cm and 8 cm intervals from the LP08 core. At least 400 valves were counted per slide and species were identified to at least genus level using taxonomic studies from the region. Microscopic pollen, charcoal and cryptotephra shards were counted at 8 cm intervals in the LP08 core) with Lycopodium spores of known concentration added for quantification. The total pollen sum from each subsample is at least 300 land pollen grains (Total Land Pollen, TLP) above 470 cm in the LP08. Charcoal was classified in five different size classes, more than 25 micrometers, 25-50 micrometers, 50-75 micrometers, 75-100 micrometers, and more than 100 micrometers, to distinguish between proximal and distal fires. Chronology A chronology was established using Accelerator Mass Spectrometry (AMS) radiocarbon dating of 21 samples. Calibration of radiocarbon ages was undertaken in OXCAL v.4.4 using the SHCal20.14C Southern Hemisphere atmosphere calibration curve (SH20). Radiocarbon ages are reported as conventional radiocarbon years BP (14C years BP) ±1sigma and calibrated ages as 2sigma (95.4%) ranges, median and mean calendar years BP (cal a BP and cal ka BP, relative to 1950 CE), rounded to the nearest ten years. Age-depth models were developed using Bayesian age-depth modelling software (rBACON v.2.5). Modelled age data mean ages produced by the SH20M1H (Southern Hemisphere, SHcal20, radiocarbon calibration curve) in rBACON, where M1 indicates Model 1 and H indicates the inclusion of a hiatus in the model. Geochemistry Contiguous downcore wet-sediment Energy Dispersive Spectrometry (EDS) X-ray fluorescence core scanning (XRF-CS) data was collected using an ITRAX XRF core scanner fitted with a Molybdenum (Mo) anode X-ray tube (settings: 30 kV, 50 mA, count time 10 seconds, at 2 mm contiguous intervals and for LP08 Unit 6 (equivalent to mean ±2-sigma: 4.5±7.0 years), at 200 micrometers intervals for LP08 Unit 1 (1.3±4.2 years), with LP08 basal Unit 1 scanned at 100 micrometers. Data from finely laminated glaciolacustrine sediments in Units 1-2 were measured at or smoothed to 200 micrometers (from 100 micrometers interval data) before analysis. Sedimentology Physical properties were measured with a Geotek multi-sensor core logger (MSCL) (gamma-ray wet density (gamma-density), resistivity and magnetic susceptibility (MSkappa; SI x 10-5) data (Bartington Instruments; LP08: MS2C loop sensor, 2 mm intervals, 10 seconds; LP16: MS2E point sensor, 0.5 mm intervals; 10 seconds) and density-corrected MSkappa (kappa/rho; kg m-3)). Digital X-radiographs were obtained from split cores using a rotating anode mobile digital Celtic SMR CR computerised X radiography unit at Cambridge University Vet School (48kV; 4 mAs; no grid) and as ITRAX generated digital X-radiographs (45 kV, 50 mA.ms, 200 ms, 60 micrometers interval) at Aberystwyth University. Subsample data includes Loss-on-ignition (LOI) (12 hrs drying at 110°C, 4 hrs at 550°C (LOI550), and 2 hrs at 950°C for carbonate-proxy (LOI950x1.36), TOC (Total Organic Carbon (%C or %Corg) and total nitrogen (%N) and carbon isotopic ratios (delta13C). Data were analysed in MATLAB v. R2021a, R v. 4.1.0/Rstudio v. 1.4.171, using the R packages Vegan, Rioja, Tidyverse, ggplot2, Ggally v. 2.1.2, and in Sigmaplot v. 14.0 and C2 v.1.7.7. Code is available from: https://github.com/stever60/Lago_Pato
description: Geochemistry ITRAX-XRF Raw count per second (cps) data were analysed using the Q-spec software v8.6.0 (Cox Analytical), with MSE values minimised to optimise the fit of 'as measured' spectra to a modelled spectrum. data are presented as percentages of the Total Scatter Normalised ratio sum (%sigmaTSN or, more simply, %TSN, which are equivalent to percentages of the cps sum, or percentage cps) to account for downcore variations in count rate, density, water and organic content. Data less than mean minus two-sigma kcps (mainly due to gaps in the core) and greater than MSE plus two-sigma (representing a poor fit between measured to modelled spectra) were filtered before analysis. 'Noisy' elements were eliminated by comparing cps and using %TSN thresholds of more than 0.1% mean and more than 0.5% maximum, and by examining autocorrelation profiles for each element (Bishop, 2021). This left 12 'measurable' elements for the LP08 record (Si, S, K, Ca, Ti, Mn, Fe, Zn, Br, Rb, Sr, Zr, and inc., coh. scatter). Elements are presented as natural log (log n or Ln) ratios. Ti-normalised log n ratios are used to estimate changes in relation to the background bedrock input. Duplicates runs were undertaken on approx10% of the total core depth (LP08-1F at 2 mm and 200 microns). Chronology Radiocarbon ages were rounded to the nearest 10 calendar years (cal a BP) in file LP08 C14 data.csv and the results section and to the nearest 100 years (0.1 cal ka BP) in the discussion to reflect dating and age-depth modelling uncertainties. Sedimentology Carbon isotope delta13C data, values were calculated to the VPDB scale using a within-run laboratory standard calibrated against NBS-19 and NBS-22. Replicate analyses of sample material gave a precision of more or less 0.1 (per mil) for delta13Corg and 10% for C/N. Flux data (g cm a-2) were calculated from the product of dry mass accumulation rates (g cm a-1), dry bulk density (g cm-3), sedimentation rates (cm a-1) and proxy concentration measurements. Geochemical XRF-Core scanning data were measured at 2 mm contiguous intervals and for LP08 Unit 6 (equivalent to mean ±2-sigma: 4.5±7.0 years), at 200micrometer intervals for LP08 Unit 1 (1.3±4.2 years), with LP08 basal Unit 1 scanned at 100 micrometers Data from finely laminated glaciolacustrine sediments in Units 1-2 were measured at or smoothed to 200 micrometers (from 100 micrometers interval data) before analysis.