What Can We Learn From X‐Ray Fluorescence Core Scanning Data? A Paleomonsoon Case Study. (3rd February 2020)

• Record Type: Journal Article
• Authors: Gebregiorgis, D.; Giosan, L.; Hathorne, E. C.; Anand, P.; Nilsson‐Kerr, K.; Plass, A.; Lückge, A.; Clemens, S. C.; Frank, M.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 21:Number 2(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-02-03
• Subjects: Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2019GC008414
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: X‐ray fluorescence (XRF) core scanning of marine and lake sediments has been extensively used to study changes in past environmental and climatic processes over a range of timescales. The interpretation of XRF‐derived element ratios in paleoclimatic and paleoceanographic studies primarily considers differences in the relative abundances of particular elements. Here we present new XRF core scanning data from two long sediment cores in the Andaman Sea in the northern Indian Ocean and show that sea level related processes influence terrigenous inputs based proxies such as Ti/Ca, Fe/Ca, and elemental concentrations of the transition metals (e.g., Mn). Zr/Rb ratios are mainly a function of changes in median grain size of lithogenic particles and often covary with changes in Ca concentrations that reflect changes in biogenic calcium carbonate production. This suggests that a common process (i.e., sea level) influences both records. The interpretation of lighter element data (e.g., Si and Al) based on low XRF counts is complicated as variations in mean grain size and water content result in systematic artifacts and signal intensities not related to the Al or Si content of the sediments. This highlights the need for calibration of XRF core scanning data based on discrete sample analyses and careful examination of sediment properties such as porosity/water content for reliably disentangling environmental signals from other physical properties. In the case of the Andaman Sea, reliable extraction of a monsoon signal requires accounting for the sea level influence on the XRF data. Plain Language Summary: X‐ray fluorescence (XRF) core scanning is an important tool of earth scientists to understand the chemical composition of natural archives (e.g., sediment cores) for reconstructing past climate change. The reliability of this tool depends on a detailed understanding of the factors that possibly affect the composition of major and trace elements in sediments and of the translation of the XRF data into elemental concentrations. In paleoceanographic and paleoclimatological studies, ratios of different elements are used to understand climate driven processes such as weathering intensity on land over longer timescale. Some of the widely used ratios of different elements to reconstruct past climate change are, however, influenced by factors that are not directly related to the climate such as amount of rainfall. Here we evaluate these factors by analyzing new data obtained by XRF core scanning of two sediment cores collected from the Andaman Sea, an area dominated by the variability of monsoon rains. We confirm that some of the elemental proxies require careful consideration of sediment properties such as porosity/water content and grain size, and regional changes in sea level, before they can be reliably used to reconstruct past environmental changes. Key Points: Calibration of XRF core scanning data highlights the need for careful examination of sediment properties such as porosity/water Grain size and water content in the sediment trigger systematic artifacts in the signal intensity of light elements (e.g., Si and Al) Known terrigenous flux proxies (e.g., Ti/Ca and Fe/Ca) are influenced by sea level variations