Supplement to Manuscript: Ohnemus and Lam, DSR-II, “Lithogenic Cycling…”
Synchrotron XRF and Ti-µXANES Methodology:
LSF images were collected by micro-focused x-ray fluorescence (µXRF) mapping
using the following collection parameters: map dimensions varied between 750µm2600µm; scale bars: 100µm; beam energy: 10keV; pixel dwell time: 50ms; pixel size:
10µm x 10µm, beam size ca. 11 x 6 µm. Extended µXANES spectra were collected by
first mapping at 5197 eV (50 eV below the Ba L3 edge, for Ti) or 10 keV (for Fe),
typically over a 500 x 500µm area of the filter, to locate Ti or Fe “hotspots”.
Extended µXANES were collected at multiple hotspots between 4930 eV and 5150
eV (Ti K-edge) or 7006-7412 eV (Fe K-edge) using a beam size of ca. 6 x 6 µm.
Primary calibrations for µXANES were to Ti and Fe-metal foils (Ti K-edge at 4966.40
eV; Fe K-edge at 7110.75 eV). Each µXANES spectrum was further calibrated against
internal energy calibrations—monochromator glitches—caused by slight
imperfections in the monochromator crystal, and thus incoming beam flux, at
known energies: 7263.55 eV for Fe; 5228.63 eV and 5234.04 eV for Ti.
Extended µXANES spectra were collected for ten to twelve Ti “hotpots” per sample,
then normalized and fitted (Lam et al, 2012) using a linear combination of up to
three model compounds from a mineral library to determine the relative endmember composition for each spot. The small but diverse library (Suppl Fig. 1)
consisted of minerals previously collected at the beamline (M. Marcus, pers. comm.):
Ti-oxides (TiO2) rutile and anatase, and the common Ti-bearing mineral phases
ilmenite (Fe2+TiO3), biotite (a mica), and augite (a pyroxene/silicate). A sixth
component, an unknown but distinct spectrum common in samples near CVI, likely
titanomagnetite due to its known frequency in local lava flows and its highly
variable Ti content (Knudsen et al., 2005), was also included. Model-fit relative
abundances were summed over all spots in a sample to estimate its overall
composition, with the caveat that each spot was weighted equally regardless of
intensity.
Supplemental Figure Captions:
Supplemental Figure 1: A) Ti K-edge µXANES spectral reference fitting library. B)
For each sample described in the text, summed linear combination fits of multiple
spectra (n=10-12 Ti “hotspots” per sample) using non-negative, scalable
contributions of components from the mineral library.
Supplemental Figure 2: Fe µXANES spectrum comparison between (lower
spectrum) 6L-ferrihydrite spectrum from ALS Beamline 10.3.2 reference library and
(upper spectrum) neutrally buoyant SSF particles on QMA filter sampled at the TAG
hydrothermal plume (station 10-16, 3300m).
Supplemental Figure 3: Animated graphics interchange format (GIF) output of 1-D
model described in model scenario 6 (Main Figure 11f), displaying time-varying SSF
and LSF concentration and size-fractionation profiles in response to variably forced
dust input.