LIP GAS EMISSION RATES: NEW METHODS USING HG CHEMOSTRATIGRAPHY AND IMPLICATIONS FOR ENVIRONMENTAL EFFECTS

Large igneous province (LIP) eruptions are among the largest volcanic events in Earth history and coincide with mass extinctions and oceanic anoxic events. However, the environmental effects coinciding with each LIP are often strikingly different, hypothesized to be a consequence of differences in average LIP eruption rates. However, LIPs are composed of 100s–1000s of individual eruptions, with potentially multi-kyr time gaps between them. As the ocean/atmosphere/carbon cycle response to external perturbations occurs on timescales ranging from years to kyrs, rather than only 100s of kyr, we hypothesize that the tempo of individual eruptions or gas emission events (rate, time between) significantly influences the environmental effects of LIPs.

Here, we use mercury (Hg) chemostratigraphy in sedimentary records along with Hg cycle box model scaling factors to understand the tempo of LIP gas emissions. We examine a few key Hg records per LIP which have good geochronological constraints and determine peak Hg enrichment factors, defined as multiples of background Hg values (explicitly considering co-variation with other geochemical parameters, e.g., TOC). As Hg reservoir timescales are short (<10 kyr between emission and deposition), these values likely reflect emissions from individual or closely spaced LIP eruptions. We compare these enrichment factors with scalings from a modern Hg cycle box model to estimate Hg emission fluxes, and then use volcanic Hg/C ratios to estimate CO₂ fluxes. We ensure that all estimates are volcanologically reasonable: consistent with volcanological properties of LIP lavas, e.g., texture (as peak eruption rate cap), approximate total equivalent volume and geochronology.

We find that peak and average LIP CO₂ emission rates significantly vary between LIPs: e.g., peak CO₂ fluxes are 1 Pg/yr (Siberian Traps), 0.5 Pg/yr (Karoo/Ferrar), and 0.4–0.5 Pg/yr (Deccan Traps). However, our average CO₂ emissions are generally lower than those estimated by reproducing paleoenvironmental proxy records using carbon cycle models, suggesting a potentially key role for carbon cycle feedback processes. Our results highlight the differences in tempo of volatile release between different LIPs and consequently have strong implications for their potential environmental impacts.