DOI: 10.5285/2031310d-1e35-4ea1-a1cc-cd318e82d394
title: Chronological, geochemical and sedimentological data from a lake sediment record extracted from Lake L15 (GPS Lake) on Potter Peninsula, South Shetland Islands in 2011

description: The dataset comprises of lake site photos, data and multiproxy data from Lake L15 (aka GPS Lake), a small lake basin at 62.24057 S, 58.6776 W on Potter Peninsula, King George Island, South Shetland Islands. The data have been used to constrain deglaciation and glacier dynamics on Potter Peninsula. Data for the Lake L15 (GPS Lake) sediment record consist of downcore measurements of chronology, geochemistry, and sedimentology proxy data collected from the depocentre in November 2011. Data collected in this study were funded by: Centro de Investigaciones en Ciencias de la Tierra (CICTERRA), the Direccion Nacional del Antartico/Instituto Antartico Argentino (DNA/IAA) in the framework of the Project PICTA, 2011 - 0102, IAA "Geomorfologia y Geologia Glaciar del Archipielago James Ross e Islas Shetland del Sur, Sector Norte de la Peninsula Antartica"; the Alfred Wegener Institute (AWI) research program Polar regions and Coasts in a changing Earth System (PACES II); IMCONet (FP7 IRSES, action no. 318718); the Natural Environment Research Council (NERC/BAS-CGS Grant no.81); the NERC/BAS science programmes CACHE-PEP: Natural climate variability - extending the Americas palaeoclimate transect through the Antarctic Peninsula to the pole and GRADES-QWAD: Quaternary West Antarctic Deglaciations. We thank the crews of the Argentine research station "Carlini" and the adjoined German Dallmann-Labor (AWI) Laboratory, the Uruguayan research station "Artigas", the Russian Bellingshausen Station, the Chinese Great Wall Station, Base Presidente Eduardo Frei Montalva, the Brazilian Navy Almirante Maximiano, the UK Navy HMS Endurance and NERC/BAS James Clark Ross for logistical support during the 2006, 2011, 2014 and 2015 field seasons.
description: Core collection: Sediment cores were collected using a Russian and Livingston corers from the deepest point (around 2 m of water depth) in Lake L15 (GPS Lake) (L15: -62.24057 degrees S, -58.67760 degrees W, around 30 m a.s.l., 11-55 cm total recovered sediment depth). Eight cores were collected from a grid of 25 (around1 m spaced) holes drilled through the around 75-100 cm thick lake ice above the deepest accessible point (around 2 m): Data from L15-H2 (-62.24057 degrees S, -58.67760 degrees W) with 30 cm of sediment and L15-H16 (-62.24056 degrees S, -58.67757 degrees W) with 55 cm of sediment are included in this dataset. Other cores taken at this site were: L15-H4 = 11 cm, L15-H9 = 39 cm, L15-H17 = 45 cm, L15-H19 = 34 cm, L15-H20 = 61 cm and L15-H22 = 49 cm. Chronology: Pb-210 Cs-137 and Am-241 dating of the uppermost 10 cm of the lake sediment records was undertaken and dating model calculations followed standard procedures defined in Appleby and Oldfield (1978). Pb-210 age estimates were derived using the constant rate of supply (CRS) method (Appleby and Oldfield, 1978) and incorporated into Bayesian age-depth models. The Pb-210 CRS age model produced a low sedimentation rate in the top 10 cm and the sample at around 4-5 cm is likely to be at least 150 years old. Radiocarbon ages of aquatic moss and macrophytic material from the uppermost lithological Unit 3 in Lake L15 were calibrated using the Southern Hemisphere SHCal20 calibration curve in Oxcal v. 4.4 (Hogg et al., 2020). Post-bomb (more than 1950 CE) ages were corrected according to 13C/12C isotopic ratios from measured pMC with the 'present day' pMC value defined as 107.5 percent (2010 CE) and calibrated using the SHCal13 SH Zone 1-2 Bomb curve in CALIBomb (Reimer and Reimer, 2004; Hua et al., 2013). Calibrated ages range from post 1950 CE to c. 0.6 ka cal BP. Geochemistry & Sedimentology: Physical properties (gamma-ray density (GRD), magnetic susceptibility, fractional porosity, resistivity and impedance) were measured using Geotek multi-sensor core logger (MSCL). Non-destructive ITRAXTM (Cox Analytical) micro-X-ray fluorescence (micro-XRF) and Bartington Magnetic Susceptibility High Resolution Surface Scanning Sensor (MS2E) measurements were undertaken at Aberystwyth University. Contiguous bulk, wet sediment geochemical Energy Dispersive XRF-CS (Energy Dispersive Spectroscopy) analysis was obtained using a chromium (Cr) X-ray tube (X-radiography image settings: 40 kV, 40 mA, 200 ms; XRF-CSCr settings: 30 kV, 40 mA, dwell time of 10 seconds, at 100 micrometer or 2 mm. Hyperspectral image (HSI) scanning was performed using the Specim Ltd. single core scanner (PFD-CL-65-V10E line scan camera, 400-1000 nm) according to the protocol of Butz et al. (2015). The spatial resolution (pixel size) was set at 69 micrometer x 69 micrometer and the spectral resolution is 2.8 nm sampled at an interval of 0.78 nm. Raw data were normalised with a BaSO4 reference and spectral endmembers were calculated using the software ENVI 5.03. Quantitative estimates of pigments were obtained using the Relative Absorption Band Depth (RABD) method, which uses ratios and normalised reflectance data from distinct wavelengths. The spectral index RABD660;670 (RABD at 660-670 nm) was calculated from the continuum between 590 and 730 nm (Butz et al., 2015) with I-band wavelengths between 660 and 670 nm using equations RABD660;670 = (6 R590+7 R730)/13/Rmin(660;670) and RABD660;670 (I-Band) = (6 R590+7 R730)/13/ Rmin(660;670)/Rmean (Rein and Sirocko, 2002). Additional statistical analysis was undertaken, and figures constructed, using R v. 4.1.0/RStudio v. 1.4.1717 (primarily packages Tidyverse, ggplot2, Vegan, Rioja, Ggally v. 2.1.2, RBacon, Rcarbon, Bchron), Sigmaplot v. 14.0, C2 (Juggins, 2007), MATLAB v. R2021a, with final layouts achieved in Adobe Illustrator v. 26.2.1 or CorelDRAW v. 2020. Code, data, all packages used, and package references can be found at: https://github.com/stever60/Potter_Peninsula
description: Chronology Pb-210 Cs-137 and Am-241 dating of the uppermost 10 cm of the lake sediment records was undertaken on a well-type gamma spectrometry (Ge-detector, GWC 2522-7500 SL, Canberra Industries Inc., USA) and processed with GENIE 2000 3.0 (Canberra Industries Inc., USA). Geochemistry and Sedimentology Geotek multi-sensor core logger (MSCL) ITRAX XRF core scanner fitted with a Molybdenum (Mo) anode X-ray tube and a Bartington Magnetic Susceptibility High Resolution Surface Scanning Sensor (MS2E) Hyperspectral image (HSI) scanning was performed using the Specim Ltd. single core scanner (PFD-CL-65-V10E line scan camera, 400-1000 nm) according to the protocol of Butz et al. (2015).
description: Chronology Pb-210 age estimates were derived using the constant rate of supply (CRS) method (Appleby and Oldfield, 1978) and incorporated into Bayesian age-depth models. The prerequisite for the CRS model was not fulfilled because the flux of Pb-210 has changed through time and is not constant, but Pb-210 data are consistent with the radiocarbon ages that show sediment between 6 and 6.5 cm dates to 620 plus-minus 80 a cal BP, and 3-3.5 cm and 0-0.5 cm depth were deposited in the 'post-bomb' (post-1950 CE) era, most likely between -40 - -44 cal yr BP (1990-1994 CE) The Cs-137 data are inconsistent with the Pb-210 CRS age model and it is possible that the steep increase in Cs-137 in the upper 2 cm relates to a Cs-137 'soil reservoir', which is leaching Cs-137 into the lake from snow or lake-ice melting. Geochemistry and Sedimentology 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 (percent sigma TSN or, more simply, percent TSN, which are equivalent to percentages of the cps sum, or percent 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 percent TSN thresholds of more than 0.1 percent mean and more than 0.5 percent maximum, and by examining autocorrelation profiles for each element. Elements are presented as natural log (log n or Ln) ratios.