Methodology:

Sediment cores were collected using a 50 cm long Russian corer from the terrestrial shoreline of Lago Pato (LP16: 51.3031 S, 72.6816 W, 33-34 m a.s.l., 295 cm long total recovered sediment depth).

Chronology

A chronology was established using Accelerator Mass Spectrometry (AMS) radiocarbon dating 15 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 ITRAXTM XRF core scanner fitted with a Molybdenum (Mo) anode X-ray tube (settings: 30 kV, 50 mA, count time 10 seconds, at 500 micrometers for LP16 Units 2-6 (9.6±17.4 years) and at 200 micometers for LP16 Unit 1 200 micrometers (1.1±1.6 years).

Tephra glass shard geochemistry was analysed using the Cameca SX-100 electron probe microanalyser (EPMA) at the Tephra Analytical Unit, University of Edinburgh with a beam diameter of 8 micrometers and run conditions: 15 keV/2 nA (Al, Ka, Si Ka, K Ka, Ca Ka, Na Ka, Mg Ka, K Ka, Ca Ka, Fe Ka); 15 keV/80 nA (P Ka, Ti Ka, Mn Ka, P Ka, Ti Ka). New shard geochemical data was compared to a database of distal tephra major element glass shard analyses from Southern South America.

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 µm 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

ITRAXTM 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 (%TotalTSN 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 (Bishop, 2021).This left 17 'measurable' elements for the LP16 record (Si , S, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Zn, As, Br, Rb, Sr, Zr , Ba, 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 (LP16-3B at 200 and 500 microns).

Chronology

Radiocarbon ages were rounded to the nearest 10 calendar years (cal a BP) in file LP16_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.

Geochemical XRF-Core scanning data were measured at 500 micrometers for LP16 Units 2-6 (9.6±17.4 years) and at 200 micrometers for LP16 Unit 1 200 micrometers (1.1±1.6 years). 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.