DOI: 10.5285/49a1ec0e-ae5f-4df5-a59b-fa6dff614678
title: Fossil diatom and geochemistry data from a 700-year core from La Grange Cop, subantarctic Marion Island.

description: This dataset contains geochemistry measurements and fossil diatom counts made on a sediment core from La Grange Cop lake, Marion Island (46deg94S, 37deg60E, 60 m above sea level). The dataset consists of diatom relative frequencies, diatom principal components analysis (PCA), and diatom-inferred conductivity, ITRAX scanning XRF elemental percentages and XRF PCA, C%, N%, and delta13C measurements, and magnetic susceptibility measurements. Ages of the sediment samples were assigned based on an age depth model derived from 210Pb, 137Cs, and 14C measurements and span the last c. 700 years. This project was funded by UK Natural Environment Research Council Grant NE/K004514/1 to Dominic A Hodgson and a Research Foundation-Flanders travel bursary to Elie Verleyen.
description: Cores were extracted from the deepest part (~4m depth) of La Grange Cop, on Marion Island (46deg56'S, 37deg35'E) using a Livingston piston core in 2013. The uppermost sediments were retrieved using a UWITEC corer, which was extruded and subsampled at 0.5 cm intervals in the field. Age determinations were made using 14C, 210Pb and 137Cs radiometric methods on bulk organic sediments. Age-depth models were generated using the software package BACON in R (Blaauw and Christen, 2011). Diatoms were isolated from the sediments using standard oxidative techniques (Renberg, 1990) and mounted on plain glass coverslips using NAPHRAX mounting medium. Taxonomic assignments were made using reference literature primarily with Van de Vijver et al. (2002) and using reference photographs to ensure consistency with the diatom-conductivity model and amongst subantarctic island analysts. At least 400 valves were identified from each slide on an Olympus BX60 microscope at 1000x magnification and phase contrast under oil immersion. PCA was performed on centered relative percentage diatom data (&gt;1% in any one sample) from the lake using the software package C2 (Juggins, 2016). Changes in bulk sediment geochemistry was undertaken on flat half-core wet sediment surfaces using an ITRAX core scanner at Aberystwyth University fitted with a Molybdenum (Mo) X-ray tube. X-radiography settings were 50 kV, 50mA, 200ms; µ-XRF; Mo settings: 30 kV, 50 mA, count time 10 seconds, 200 µm or 2 mm interval with 50- or 5-point moving average for 1 cm subsample interval equivalence. Machine and sample calibration was undertaken using a synthetic glass standard and XRF fused glass discs from the core at the start and end of each core-site run. Raw count per second (cps) data were analysed using the Q-spec spectra matching software (Cox Analytical). Data are presented as percentages of the total scatter-normalised sum, following established total-scatter normalisation procedures (Kylander et al., 2011; Davies et al., 2015), rather than equivalent whole-rock percentages. The uppermost sediments were flocculent and could not be preserved intact for scanning. Magnetic susceptibility (MS) (Bartington Instruments MS2G 1 cm loop sensor, 10 s) was measured with a GEOTEK core logger using standard calibration procedures (Gunn and Best, 1998). Sediments were placed in 5% HCl to remove any CaCO3, then washed over Whatman 41 filter papers with deionised water and dried at 40degC in a drying cabinet. Carbon isotope ratios (delta13C), percentage total organic carbon (%TOC) and percentage total nitrogen (%TN were analysed during combustion in a Carlo Erba 1500 on