Methodology:

Core collection

Sediment cores were collected using a Livingston piston corer from the deepest point(~5 m of water depth) in Matias Lake (L5: 62.2450°S, 58.6655°W, ~70-75 m a.s.l., 20-30 cm total recovered sediment depth). We extracted 13 short cores from the depocentre in Matias Lake and along a surface transect towards Rudy Lake. Sediment recovery depth ranged from 20 and 60 cm before encountering an impenetrable diamicton layer. Data from cores MAT1 (L5-H1) (27 cm) and MAT2 (L5-H2) (29 cm) extracted from the deepest part of Matias Lake (5.8 m; 62° 14' 42.054"S, 58° 39' 53.82"W) are included in this dataset.

Chronology

Obtaining basal radiocarbon ages from basal and bulk minerogenic sediments in the Matias Lake cores proved challenging due to a general lack of organic carbon. 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 Constant Rate of Supply (CRS) age model shows that the uppermost 10 cm have been deposited since c. 1850 CE, and the well-defined 137Cs peak at 5 cm depth is coherent with the Pb-210 age model.

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 micrometers 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 micrometers x 69 micrometers 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

Data collection:

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 & Sedimentology

ITRAX XRF core scanner fitted with a Molybdenum (Mo) anode X-ray tube and a Bartington Magnetic Susceptibility High Resolution Surface Scanning Sensor (MS2E)

Geotek multi-sensor core logger (MSCL)

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).

GEOTEK MSCL data were measured at 2 mm intervals

Geochemical XRF-Core scanning data were measured at 100 μm and 2 mm contiguous intervals.

SPECIM hyperspectral data were measured at 69 μm intervals

Data quality:

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.

Geochemistry & 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 (%sigmaTSN or, more simply, %TSN, which are equivalent to percentages of the cps sum, or %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 >0.1% mean and >0.5% maximum , and by examining autocorrelation profiles for each element. Elements are presented as natural log (log n or Ln) ratios.