LASS-ICP-MS collection of trace element and 87Sr/86Sr isotope data using a novel uneven distribution of sample material for otolith microchemistry
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Date
2022-01-26
Authors
Edgeworth, Ivan
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Publisher
University of Waterloo
Abstract
Understanding the behaviour and movement of fish populations is crucial to developing plans to properly manage fisheries, and to predict effects of ongoing environmental change. In northern regions, physically tracking fish populations is difficult and expensive for researchers to accomplish at spatial scales that are relevant for populations. Otoliths (fish ear bones) are comprised of metabolically inert aragonite that stores elemental and isotopic data throughout the lifetime of a fish in seasonal growth bands centered around a nucleus.
Previous LA-ICP-MS studies have utilized trace element and isotopic data gathered from otoliths to investigate fish migration patterns, discriminate stocks, spawning and rearing sites, and reconstruct characteristics of habitats used, such as relative temperature or pH. Otolith structures can be small and fragile, depending on the species of fish, and may only have room for a single laser transect. Most previous LA-ICP-MS studies have measured isotopic or trace element data across a single transect, limiting the amount of information that can be acquired from a single otolith.
This thesis focuses on the development of a new analytical technique that simultaneously quantifies trace element and strontium isotope ratios from a single line transect. A novel, uneven distribution of material in a split-stream configuration couples the laser ablation system with two mass spectrometers. Long-term accuracy assessments of trace element concentrations indicate that measured values are within 5 – 10% of accepted/preferred values of standard reference and in-house reference materials. Isotopic precision varied with respect to laser diameter but is generally fit-for-purpose for otolith studies.
The utility of this innovative split stream technique is demonstrated by analyzing three transects on otoliths from two species of fish (lake trout (Salvelinus namaycush) and arctic char (Salvelinus alpinus)). Transects of lake trout and arctic char (25µm and 40µm laser diameter, respectively) were analyzed and assessed, and results indicated that larger laser diameters yield more accurate and precise data without sacrificing significant spatial resolution.
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Keywords
geochemistry, otolith, laser ablation, split-stream