Synchrotron X‐ray fluorescence spectroscopy of salts in natural sea ice

• Published in: Earth and space science (Hoboken, N.J.) Vol. 3; no. 11; pp. 463 - 479
• Main Authors: Obbard, Rachel W., Lieb‐Lappen, Ross M., Nordick, Katherine V., Golden, Ellyn J., Leonard, Jeremiah R., Lanzirotti, Antonio, Newville, Mathew G.
• Format: Journal Article
• Language: English
• Published: Hoboken John Wiley & Sons, Inc 01.11.2016; American Geophysical Union (AGU)
• Subjects: Atmosphere; Atmospheric chemistry; Blowing snow; Bromine; Calibration; ENVIRONMENTAL SCIENCES; Fluorescence; Grain boundaries; Ice; OTHER INSTRUMENTATION; Ozone depletion; Salinity; Salts; Sea ice; Snowpack; Spectroscopy; synchrotron; X-ray fluorescence spectroscopy; United States > US
• ISSN: 2333-5084; 2333-5084
• DOI: 10.1002/2016EA000172

We describe the use of synchrotron‐based X‐ray fluorescence spectroscopy to examine the microstructural location of specific elements, primarily salts, in sea ice. This work was part of an investigation of the location of bromine in the sea ice‐snowpack‐blowing snow system, where it plays a part in the heterogeneous chemistry that contributes to tropospheric ozone depletion episodes. We analyzed samples at beamline 13‐ID‐E of the Advanced Photon Source at Argonne National Laboratory. Using an 18 keV incident energy beam, we produced elemental maps of salts for sea ice samples from the Ross Sea, Antarctica. The distribution of salts in sea ice depends on ice type. In our columnar ice samples, Br was located in parallel lines spaced roughly 0.5 mm apart, corresponding to the spacing of lamellae in the skeletal region during initial ice growth. The maps revealed concentrations of Br in linear features in samples from all but the topmost and bottommost depths. For those samples, the maps revealed rounded features. Calibration of the Br elemental maps showed bulk concentrations to be 5–10 g/m3, with concentrations ten times larger in the linear features. Through comparison with horizontal thin sections, we could verify that these linear features were brine sheets or layers. Plain Language Summary Synchrotron‐based X‐ray fluorescence spectroscopy at the Advanced Photon Source at the Argonne National Laboratory is used to examine the microstructural location of specific elements, particularly Br, in Antarctic sea ice. In columnar ice, Br concentrations were ten times larger in parallel lines spaced ~0.5 mm apart than in the sampled area as a whole. Through comparison with thin sections, we verified that these linear features were brine sheets or layers formed as the ice grew. Key Points Synchrotron X‐ray fluorescence spectroscopy maps salts in sea ice Bromine concentration in brine inclusions is ten times the bulk concentration