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We regularly host online and in-person meetings as a great way to network. Our webinars focus on a variety of topics, both diversity-related and technical talks. We have hosted and supported courses as well. 

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Women Geoscientists in Canada February Webinar

Thursday, February 22nd, 2024 at 13:00 PST


Speaker: Kathryn Cheng

Title: Assessing Volcanism during the SPICE Event using Mercury Stable Isotopes

The Steptoean Positive Carbon Isotope Excursion (SPICE) event signified a large global carbon isotope excursion and carbon cycle perturbation during the Cambrian Period (ca. 497 – 494 Ma). The trigger for the SPICE event is still debated and the role of volcanism is unknown. Mercury (Hg) and Hg isotope chemostratigraphy in sedimentary units are growing proxies to trace Large Igneous Province (LIP) volcanism, changes in terrestrial weathering and in carbon cycling. Prior to human activity, the major primary source of Hg to surface environments was volcanism with marine sediments being the major sink. Hg mainly enters marine sediments, where it is sequestered mostly by organic carbon, via terrestrial runoff or atmospheric deposition. Volcanic Hg and the two main deposition pathways can each have distinct isotopic compositions allowing for various changes in Hg cycling to be assessed with Hg isotopes. This project uses Hg and Hg stable isotopes to determine if volcanism played a role during this major carbon cycle perturbation in the Cambrian Period – as previously thought. In this study, we analyzed Hg concentrations and isotopic compositions in marine sediments from the Alum Shale Formation (Sweden). The Hg concentrations ranged from 39.5 ng/g to 864 ng/g with an average concentration of 290 ng/g. Typically, modern marine sediments with Hg concentrations greater than 100 ng/g are associated with pollution (i.e., an increase in inputs) or high total organic carbon (TOC) content. The TOC (%) content in the Alum Shale is high, ranging from 1.5% to 17% with an average of 8.5%, with increases in TOC correlating with increases in Hg content (R2 = 0.60). To assess increases in an external input such as volcanism, Hg is often normalized to TOC. Hg/TOC ratios range from 23 to 43 ppb/wt%, which are not elevated compared to sediments with no increases in external sources, indicating that the high Hg contents are likely associated with higher organic carbon, either through preservation or a reduction in diluting sedimentary components (siliciclastics). Furthermore, both the δ202Hg (MDF) and Δ199Hg (MIF) exhibit isotopic compositions consistent with atmospheric Hg deposition followed by near complete scavenging of the Hg from the water column. Overall, Hg and Hg isotopes do not support increased volcanic activities during the SPICE event.

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