Publication Date:
2022-05-26
Description:
This paper is not subject to U.S. copyright. The definitive version was published in Environmental Chemistry 11 (2014): 10-17, doi:10.1071/EN13075.
Description:
It is a well known truism that natural materials are inhomogeneous, so analysing them on a point-by-point basis can generate a large volume of data, from which it becomes challenging to extract understanding. In this paper, we show an example in which particles taken from the ocean in two different regions (the Western Subarctic Pacific and the Australian sector of the Southern Ocean, south of Tasmania) are studied by Fe K-edge micro X-ray absorption near-edge spectroscopy (μXANES). The resulting set of data consists of 209 spectra from the Western Subarctic Pacific and 126 from the Southern Ocean. We show the use of principal components analysis with an interactive projection visualisation tool to reduce the complexity of the data to something manageable. The Western Subarctic Pacific particles were grouped into four main populations, each of which was characterised by spectra consistent with mixtures of 1–3 minerals: (1) Fe3+ oxyhydroxides + Fe3+ clays + Fe2+ phyllosilicates, (2) Fe3+ clays, (3) mixed-valence phyllosilicates and (4) magnetite + Fe3+ clays + Fe2+ silicates, listed in order of abundance. The Southern Ocean particles break into three clusters: (1) Fe3+-bearing clays + Fe3+ oxyhydroxides, (2) Fe2+ silicates + Fe3+ oxyhydroxides and (3) Fe3+ oxides + Fe3+-bearing clays + Fe2+ silicates, in abundance order. Although there was some overlap between the two regions, this analysis shows that the particulate Fe mineral assemblage is distinct between the Western Subarctic Pacific and the Southern Ocean, with potential implications for the bioavailability of particulate Fe in these two iron-limited regions. We then discuss possible advances in the methods, including automatic methods for characterising the structure of the data.
Description:
The operations of the Advanced Light Source at Lawrence Berkeley
National Laboratory are supported by the Director, Office of Science, Office
of Basic Energy Sciences, US Department of Energy under contract number
DE-AC02-05CH11231. Collection of samples for the VERTIGO project
was supported by the US National Science Foundation Program in Chemical
Oceanography to Ken Buesseler and the US Department of Energy, Office of
Science, Biological and Environmental Research Program to Jim Bishop.
The SAZ-SENSE project was supported by the Australian Government
Cooperative Research Centres Programme. Collection of spectroscopic data
by PJL was supported through the WHOI Postdoctoral Scholar Program,
WHOI Independent Study Award and NSF Chemical Oceanography.
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
application/pdf
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