Analyzing the joint effect of volcanic carbon and sulfur emissions on
the marine 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 a posteriori. In this study, we explore the
complex and interconnected effects of volcanic gas emissions from LIPs
on the ocean-atmosphere system and biosphere by analyzing the joint
effect of CO2 and SO2 using a biogeochemical carbon cycle box
model (LOSCAR). Using a range of volcanic gas forcings as well as models
with and without volcanic SO2 emissions, we find that sulfur
emissions have significant long-term (>1000 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 1000 year timescale for ocean
overturning circulation. Thus, the effects of volcanic sulfur are not
simply additive to the impact of carbon emissions. We also develop a
causal mechanistic framework to understand and visualize the impacts of
combined carbon and sulfur emissions, focusing on determining the
feedback amplitudes and characteristic timescales. Our results
underscore the critical need to unravel the complex feedback mechanisms
within the Earth system to understand the diverse environmental
responses triggered by large-scale volcanism over geological time
scales.