Methodology:

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

Data quality:

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 200 μm intervals for LP08 Unit 1 (1.3±4.2 years), with LP08 basal Unit 1 scanned at 100 μm. Data from finely laminated glaciolacustrine sediments in Units 1-2 were measured at or smoothed to 200 μm (from 100 μm interval data) before analysis.