Large Igneous Province Sulfur Emissions Have Long-Term (>1000 Years) Effects on the Ocean Carbon Cycle

Abstract

Large Igneous Province (LIP) eruptions are thought to have driven environmental and climate change over wide temporal scales ranging from a few to thousands of years. Since the radiative effects and atmospheric lifetime of carbon dioxide (CO₂, warming) and sulfur dioxide (SO₂, cooling) are very different, the conventional assumption has been to analyze the effects of CO₂ and SO₂ emissions separately and add them together afterward. In this study, we test this assumption by analyzing the joint effect of CO₂ and SO₂ on the marine carbonate cycle using a biogeochemical carbon cycle box model (Long-term Ocean-atmosphere-Sediment CArbon cycle Reservoir Model). By performing model runs with very fine temporal resolution (∼0.1-year timestep), we analyze the effects of LIP carbon and sulfur gas emissions on timescales ranging from an individual eruption (hundreds to thousands of years) to the entire long-term carbon cycle (>100,000 years). We find that, contrary to previous work, sulfur emissions have significant long-term (>1,000 years) effects on the marine carbon cycle (dissolved inorganic carbon, pH, alkalinity, and carbonate compensation depth). This is due to two processes: the strongly temperature-dependent equilibrium coefficients for marine carbonate chemistry and the few thousand-year timescale for ocean overturning circulation. Thus, the effects of volcanic sulfur are not simply additive to the impact of carbon emissions. We develop a causal mechanistic framework to visualize the feedbacks associated with combined carbon and sulfur emissions and the associated timescales. Our results provide a new perspective for understanding the complex feedback mechanisms controlling the environmental effects of large volcanic eruptions over Earth history.