Synchrotron imaging and spectroscopy of sulfur and other low Z elements at the National Synchrotron Light Source II (NSLS-II) X-ray Fluorescence Microprobe (XFM) with examples from marine biogeochemistry

Abstract:

At the X-ray fluorescence microprobe (XFM) beamline at the NSLS-II synchrotron light source, we have built and commissioned a low Z experimental chamber with an xyz piezomotor sample stage in order conduct experiments with low Z elements on their own and co-located with hard-X-ray transition metals. Commissioning testing has been successful on marine, terrestrial, and extraterrestrial samples. In this contribution we describe commissioning experiments examining sulfur speciation and distribution in marine samples.

Sulfur is an essential component of all living cells, usually as metal sulfides or organosulfur compounds. Plants roots take in S as sulfate, reduce it to sulphite, then to sulfide, and then incorporate it into cells as organosulfur compounds (eg. cysteine and methionine). Sulfur is a constituent of many rock-forming minerals in terrestrial and extra-terrestrial systems. Sulfate is a major anion of natural waters and can be a significant constituent of calcareous organisms. Chemically reduced sulfur species are a key component of primary productivity potential via chemosynthesis in hydrothermal vent fluids and plumes (Cron et al 2020).

The speed of the stage in the Low Z experimental chamber and of the flyscanning monochromotor allows XFM to take advantage of the high flux from NSLS-II while minimizing sample exposure to photodamage. The process of changing configuration of the instrument to move from measurements in the hard X-ray range to the tender X-ray range takes less than 10 minutes, and requires no change or movement of the mounted sample. This allows multielement spectroscopy at the same point on the sample in a short amount of time.

The figures show XRF images and spectroscopy collected at XFM on two marine samples, a hydrothermal sulfide chimney from Juan de Fuca ridge (Toner et al 2009), and a coldwater coral Lophelia collected at depth in the NE Atlantic via remotely operated vehicle from the Irish research vessell R/V Celtic Explorer.

Cron et al. 2020 ACS Earth and Space Chemistry 4(2) 168-182.

Toner et al 2009 Geochimica et Cosmochimica Acta 73 (2) 388-403.

We wish to acknowledge the R/V Celtic Explorer, Professor Louise Allcock, and Dr. Ryan Young of the National University of Ireland, Galway for the coral sample.