Understanding the impact of millennial to sub-decadal climate and limnological change on the stability of As in lacustrine sediments

Abstract

Metal(loid)s are expected to respond to 21st century warming as their stability in lacustrine systems is indirectly influenced by regional temperature and precipitation. In the Northwest Territories (NT), arsenic (As) is a metal(loid) of environmental concern due to elevated concentrations in bedrock and widespread mining-related contamination. To characterize the response of As to long-and short-term climate variability, we developed techniques that enable high temporal resolution analyses of sediment freeze cores, and applied them to a sediment cores (CON01, CON02) recovered from Control Lake, NT. New equipment was designed to enable Itrax X-ray fluorescence (Itrax-XRF) analysis of discrete sediment samples (Chapter 2). This equipment was used to test calibration methods that convert semi-quantitative Itrax-XRF results to near-total geochemical concentrations (Chapter 3). We found that the multi-variate log-ratio calibration provided the best approximation of actual geochemical concentrations. Subsequently, equipment was designed to permit scanning of freeze-cores using Itrax-XRF (Chapter 4). To characterize millennial-scale shifts in sedimentary As concentration in response to climate change, Arcellinida and ICP-MS analysis were conducted on core CON01 that recorded 4000 yr of sedimentation (Chapter 5). Arsenic concentrations the in core were related to shifts in the proportion of organic matter and shifts in minerogenic content (Rb, K). Comparison to regional records suggests changes in temperature impacted autochtonous productivity, which is hypothesized to have influenced sedimentary As concentrations. To characterize the response of As to quasi-periodic climate oscillations, CON02 was analyzed using Itrax-XRF. Itrax-XRF data were calibrated to paired ICP-MS data, and geochemical proxies for particle size (log(Zr/Ti)), in-lake productivity (log(Ca/Ti)), and As preservation (log(As/Ti)) were examined for cyclities using spectral and wavelet analyses. Periods of 8-15, 30-60, 90-130, and 180-300 yr were observed in all proxies. These periods are temporally related to the North Atlantic Oscillation/El niño/Schwabe sunspot cycles, the Pacific Decadal Oscillation, the Gleissberg cycle, and the Suess cycle, respectively. Cross-wavelet analysis of the paleo-proxies vs. published total solar irradiance reconstructions demonstrate significant relationships, suggesting a solar influence on climate and lake sediment geochemistry in the NT. These results suggest that As sequestration is impacted by short-period climate perturbations. Gregory et al 2019 iii Acknowledgments First and foremost, thank you to my co-supervisors Dr. Jennifer Galloway and Dr. Timothy Patterson, whose passion for science and support helped make this dissertation a reality. Thank you for pushing me to publish and present. Thank you to Dr. Eduard Reinhardt. You took me on as an undergraduate student and put me on the path to academia. Without your guidance I would not be into science, coffee or baking as I much as I am today. Thank you to my colle...

Application of Metabolomics for the Detection and Evaluation of Cyanopeptide Mixtures in Ontario and Quebec Lakes

“…Within the last few decades, Xray fluorescence (XRF) core scanners have become increasingly utilized in for geochemical analyses in paleoenvironmental research. New-age Itrax-XRF core scanners are capable of providing high-resolution imagery, X-ray fluorescence (XRF), and magnetic susceptibility data at 0.1 mm resolutions [226][227][228][229] . The high resolution provided by Itrax-XRF can enhanced interpretation of climate signals at resolutions difficult to achieve by other traditional analysis.…”

“…The high resolution provided by Itrax-XRF can enhanced interpretation of climate signals at resolutions difficult to achieve by other traditional analysis. The lack of sample preparation, minimal analysis time, high resolution, and non-destructive nature of Itrax-XRF analyses make it an efficient and effective choice for whole sediment core analyses 227,228 . Itrax-XRF analyses provide semi-quantitative data, a limitation due to the analysis of non-dry sediment at high resolution however, drying of samples prior to analysis can assist this variability.…”

“…For stratigraphic interpretation of Itrax-XRF results, constrained incremental sum of squares (CONISS) cluster analysis was applied to (Ti, Zr, Sr, Fe, Rb, Mg, K, Ca CIR, S, P, Si, Cl) to provide delineation of major shifts in lake environmental conditions over time. Ratios of select elemental This included, major decreases in abundant element concentrations such as Fe, substantial decreases in the ratio of coherent/incoherent backscatter, and knowledge of SSR compartment well length and position 228,247,248 . Further normalization of the data to reduce matrix effects used the mean square error (MSE) and coherent/incoherent X-ray backscatter ratio (CIR).…”

Geochemical and Sedimentological Evidence of Paleoclimatic Change in a Late Holocene Freeze Core Record from Walsh Lake, Northwest Territories

“…Two As peaks may therefore be observed in sediment cores: a primary peak from the time of deposition, and a secondary peak from remobilization (Martin & Pedersen, 2002;Andrade et al, 2010;Gavel et al, 2018;Schuh et al, 2018). As a result, the absolute concentration of As over time in these systems cannot be reliably measured using sediment geochemistry, but the general trends may be understood (MacDonald et al, 2005;Gregory, 2019).…”

“…Lacustrine OM, particularly the labile S2 fraction, is also known to scavenge and concentrate Hg, acting as an important determinant in Hg sequestration (Sanei & Goodarzi, 2006;Sanei et al, 2012Sanei et al, , 2014Outridge et al, 2019). In the 20 th and 21 st centuries, warming in northern regions has resulted in greater autochthonous primary productivity within lakes, which has been linked to increases in sedimentary storage of Hg (Outridge et al, 2007, 2019Stern et al, 2009;Jiang et al, 2011). The negative correlation of Hg with S1 (rs = −0.6, p < 0.001, n = 42) and S2 (rs = −0.3, p = 0.027, n = 42), and the apparently stable Hg levels between 50 cm and 12 cm depth, are thus unexpected and merit further investigation.…”