Volcano/Tectonic Climate Interactions

Volcanism is the primary pathway linking the solid Earth with the climate, and it has the potential to strongly perturb the biosphere, e.g., mass extinctions, on a range of timescales from a fraction of a year (e.g., direct effects of a large eruption) to longer timescales (~1 kyr - 100s kyr) due to compound effects of multiple eruptions and Earth system feedbacks. 

However, current models do not accurately represent these timescales, as they focus either on individual eruptions (~ years) or long-term carbon cycle effects of volcanism (~100 kyr, focusing on CO2 emissions only). Specifically, we need to model how volcanic emissions other than CO2 (e.g., volcanic ash, SO2/SO4 aerosols, halogens, hydrothermal nutrient flux) affect the climate over multiple eruptions. My research addresses this challenge by a) developing novel data analysis methods to estimate the tempo of eruptions at < 10 kyr resolution, b) developing new models to assess the environmental impact of multi-eruption sequences, and c) comparing model predictions with high-resolution paleoclimate records. During my PhD, I focused on continental flood basalts (CFBs) since they are the best examples of volcano-climate-ecosystem interaction.

 I have utilized a variety of multi-disciplinary approaches to provide the first, robust estimates of eruptive rates for CFBs at the scale of individual eruptions. These include constraints from volcanology (lava flow morphology and thickness, Self, Mittal et al. 2020; lava flow thermal modeling Katona, Fu, Mittal et al. 2020; lava flow plagioclase textures in thin sections - both across different basaltic lavas as well as a function of depth in a single flow; Monteiro, Mittal et al. 2024), geochronology (Sprain … Mittal et al. 2019, Fendley … Mittal et al. 2020), paleo-proxy records (analysis of Deccan Traps Hg records with data inversion methods; Fendley, Mittal et al. 2019 as well as ongoing work on MCMC data inversion), and paleomagnetism (analysis of flow-by-flow paleo-secular variation using forward models and data inversion, Mittal et al. 2019 and ongoing work). 

Overall, our analysis suggests that : 

1)   Individual LIP eruptions are much larger than modern basaltic volcanism​

~ 1000 km3 (or larger)​

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2)   Average eruption rates of individual LIP flows are broadly similar to largest historical basaltic eruptions : ​~ 20-100 km3/yr erupting for 10 – 100s of years  ​

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3)  LIPs typically have > 50 individual eruptions with​ 100 – 10,000s years between eruptions

In parallel, I am working on using carbon cycle models to analyze the joint effects of volcanic carbon and sulfur emissions on the marine carbon cycle as well as understanding how seafloor bathymetry (and its variations over the past 80 Myr) affect the ocean carbon chemistry and Carbonate Compensation Depth on Myr timescales (Bogumil, Mittal. et al. 2024 PNAS). 

We found that the joint effect of volcanic S and C emissions is NOT simply additive, as is typically assumed since rapid cooling can affect the ocean carbonate chemistry, leading to increased carbon dissolution into the ocean and faster recovery of the system back to equilibrium (Hee Jun, Mittal, et al. in prep). This feedback is missing in current models, and our analysis highlights the need to properly resolve the coupled C and S emission effects in Earth system models to understand the full impact of large eruptions, e.g., in large igneous provinces. 

Our PNAS 2024 study found that the shape and depth of the ocean floor explain up to 50% of the changes in depth at which carbon has been sequestered in the ocean over the past 80 million years. Thus, changes in seafloor topography over Earth’s history can strongly affect the ocean’s ability to sequester carbon, a poorly understood process. Typically, carbon cycle models over Earth’s history consider seafloor bathymetry as either a fixed or a secondary factor. Understanding important processes in the long-term carbon cycle can better inform scientists working on marine-based carbon dioxide removal technologies to combat climate change today. By studying what nature has done in the past, we can learn more about the possible outcomes and practicality of marine sequestration to mitigate climate change.

Overall, the results serve as a basis to develop a process-based understanding of how volcanism and tectonic processes affect the carbon cycle and ocean dynamics.