Volcanic glass properties from 1459 C.E. volcanic event in South Pole ice core dismiss Kuwae caldera as a potential source

A large volcanic sulfate increase observed in ice core records around 1450 C.E. has been attributed in previous studies to a volcanic eruption from the submarine Kuwae caldera in Vanuatu. Both EPMA–WDS (electron microprobe analysis using a wavelength dispersive spectrometer) and SEM–EDS (scanning electron microscopy analysis using an energy dispersive spectrometer) analyses of five microscopic volcanic ash (cryptotephra) particles extracted from the ice interval associated with a rise in sulfate ca. 1458 C.E. in the South Pole ice core (SPICEcore) indicate that the tephra deposits are chemically distinct from those erupted from the Kuwae caldera. Recognizing that the sulfate peak is not associated with the Kuwae volcano, and likely not a large stratospheric tropical eruption, requires revision of the stratospheric sulfate injection mass that is used for parameterization of paleoclimate models. Future work is needed to confirm that a volcanic eruption from Mt. Reclus is one of the possible sources of the 1458 C.E. sulfate anomaly in Antarctic ice cores.


Supplementary information Mounting Methodology
This study utilizes a refined methodology for extraction of cryptotephra particles from ice core samples that is based on [1]. The ice core is decontaminated and sectioned in an ultra-clean freezer laboratory into samples following a yearly sampling regime determined by the timescale. The individual samples are then melted in a clean 0.7 L Whirl-Pak bag. Meltwater is transferred into centrifuge vials and spun at 7000 rpm for 15 minutes. One milliliter of sample from the bottom of each centrifuge tube is then evaporated on a pre-heated hot plate at 60-70 • C inside of a specially manufactured sample ring mount holder. The water is slowly deposited inside a mount to the glue side of a piece of single-sided Kapton tape, which is supported by an ultra-flat metal surface. Once all water is evaporated for the selected sample, the ring mount is back-filled with Buhler Epo-Thin 2 epoxy resin and hardener, and left overnight to cure under room temperature. Once the epoxy is cured, the mount is detached from the tape, with all embedded particles exposed at the surface. Previous test experiments have shown that no chemical residue remains from the interaction between the tape adhesive and any insoluble particles. All mounts are carbon-coated prior to analysis.

Cryptotephra geochemical analysis
Scanning electron microscopy analysis using an energy dispersive spectrometer (SEM-EDS) Because most particles were smaller than 10 µm, sample mounts were not polished before SEM/EDS geochemical analysis. Concentrations of major and minor oxides: SiO 2 , TiO 2 , Al 2 O 3 , FeO, MgO, CaO, Na 2 O, and K 2 O were measured via secondary electron beam x-ray microanalysis using the University of Maine's Tescan Vega XMU scanning electron microscope. The sample mounts were coated with a 15nm layer of carbon using an Emitech high vacuum evaporator. Particles were analyzed with a 15kV beam scanned over a 1-2 µm area using a 40 mm 2 EDAX Apollo TM energy dispersive x-ray detector and EDAX Genesis TM software. Each analysis accumulated the x-ray spectra for 100 seconds of live time over one analytical spot, and the net peak intensities were converted to oxide weight percent using a standardless, PhiRhoZ-based correction [2]. An additional EDAX Genesis TM PhiRhoZ correction was calculated for tephra using the Smithsonian Rhyolite Glass (NMNH 72854 VG-568).

Dataset Figure1
File: Fig1.gmt, provides "bash" script used to generate Fig. 1. An additional free data set is required to map grounding and hydrostatic lines for the Antarctic Ice Sheet. A link to the data set is provided within the file Fig1.gmt. The file also contains a list of ice cores and coordinates of volcanic centers from the Smithsonian global volcanism program database.
Table: S1 provides a list of data sources for mapping sulfate deposition in Antarctica captured in Fig. 1 from [5][6][7]

Dataset Figure2-S3
Folder contains the following files: FigHarker.R is a R programming language script that generates Fig. 2 and S3 plots.
SPICEcoreTephraSEM.csv SEM data from the  Figure S1: SPICEcore conductance variation with depth. Volcanic glass particles used in this study were found in sample AntT 336. No cryptotephra particles were found in sample AntT 335. An optical scan image [15] acquired during ice core processing at the U.S. NSF Ice Core Facility (on the right) shows no visible tephra deposit at this depth.  [17], and SPICE (this study) are based on Figure 3 in [5]. Cryptotephra was extracted from the grey filled section on the SPICEcore subplot.