The impact of cyclical, multi-decadal to centennial climate variability on arsenic sequestration in lacustrine sediments

Abstract

Examining paleoclimate-driven changes of elemental contaminants, such as Arsenic (As), increases the understanding of the mobility and fate of elements under a warming climate scenario. To characterize the variability in As sequestration in the sediments of a freshwater system in response to decadal- to centennial-scale climate oscillations, a freeze-core (CON01) was recovered from Control Lake, Northwest Territories. Radiocarbon dating of 13 bulk-organic samples provided temporal reference to core depth. Sediment geochemistry was determined using Itrax X-ray fluorescence core-scanning (Itrax-XRF). Elemental concentrations were measured on a sub-set of samples using ICP-MS after multi-acid (MA) digestion to assess the accuracy of Itrax-XRF results through a multivariate log-ratio (MLC) calibration. Comparison of Itrax-XRF to ICP-MS using the MLC in ItraXelerate software show Pearson's R2 values >0.75, with the exception of As (R2 = 0.44). MLC-calibrated Itrax-XRF elemental data were centered log-ratio (CLR) transformed to eliminate issues related to data closure. During the ca. 3300-yr sedimentary record, moderate-strength negative correlations between AsCLR and KCLR (Spearman's ρ = −0.38, p-value < 0.001, n = 785), and AsCLR and TiCLR, (Spearman's ρ = −0.52, p-value < 0.001, n = 785) suggest that As is primarily sequestered in sediments during intervals of warmer temperatures and higher productivity. Proxies for sediment particle size (TiCLR, KCLR) and As concentration (AsCLR) were examined for response to quasi-periodic climate oscillations using spectral analysis. Significant periodicities were observed with approximately 4–13, 30–60, 90–120, and 160–280 yr periods in TiCLR, KCLR, and AsCLR records. These frequencies are interpreted as corresponding to the North Atlantic Oscillation and/or 8–14-yr Schwabe sunspot cycles, 30–60-yr Pacific Decadal Oscillation, and centennial-scale solar cycles (e.g., 90-yr Gleissberg cycle; 205-yr Suess cycle). Coeval occurrence of these periodicities revealed through wavelet analysis of Control Lake geochemistry data suggests that these climate cycles only impact Control Lake when they occur concurrently.