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

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.