Stable Barium Isotopes : Biogeochemical Cycling and Palaeoceanographic Applications

• Main Author: Yu, Yang
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: Antarctic; Antarc*; NADW; North Atlantic Deep Water; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/53775/; https://oceanrep.geomar.de/id/eprint/53775/1/2021,%20Yu,%20Thesis,%20Fulltext.pdf; https://macau.uni-kiel.de/receive/macau_mods_00001491

Stable barium (Ba) isotopes have received increasing attention in the past decade as a result of improved analytical precision and their potential as a tracer for ocean circulation and for palaeoceanographic reconstructions. However, challenges exist regarding the isotope analysis and interpretation of this emerging isotopic tracer. The first major challenge is the accurate and precise determination of the natural stable Ba isotope fractionation (δ138Ba) in various samples matrices, such as seawaters, river waters, carbonates, sulphates and sediments. Multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS) offers rapid sample throughput for stable Ba isotope analysis, but suffers from severe matrix effects caused by changes in matrix load and instrumental mass bias variations during the measurements. While significant efforts have been invested into improving chemical purification and refining the models of mass bias correction, the impact of plasma conditions has rarely been considered. In this thesis, a detailed investigation of non-spectral matrix effects on the accuracy and precision of stable Ba isotope analysis has been carried out under different plasma conditions quantified by the Normalised Argon Index (NAI). Based on the results of our experiments, a new approach is proposed to address how the matrix effects can be attenuated by optimising the NAI, which minimises and stabilises the instrumental mass fractionation. The improved understanding of the behaviour of the matrix-induced mass bias allows us to define a matrix tolerance state for stable Ba isotope analysis with MC-ICP-MS. The second challenge in the study of oceanic Ba isotope systematics is a lack of constraints on the dissolved Ba isotope composition of endmember water masses in the high-latitude oceans. The modern deep ocean circulation system is largely driven by the sinking of cold, saline water masses in high latitudes, where North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) acquire their respective Ba ...