Ecosystem-to-global scale modeling of vegetation-climate feedbacks during the Late Paleozoic Ice Age

Abstract:

The Late Paleozoic Ice Age (LPIA; ~340-270 Ma), Earth’s penultimate icehouse and a time of widespread coal formation, experienced the evolution and expansion of the oldest and most extensive paleotropical forests. Increasing evidence suggests that repeated restructuring of terrestrial ecosystems during the LPIA occurred in step with changes in atmospheric CO₂, aridity, and high-latitude ice volume, supporting the hypothesis that pre-angiosperm biomes exerted a strong influence on the climate system. Land surface models have been used to simulate the role of vegetation-climate feedbacks in past climate change. However, the representation of plants in land surface models is typically based on modern angiosperms and conifers, which may be poor physiological analogs for Late Paleozoic plants. Recent work has quantified key parameters of physiological functioning of extinct plants from well-preserved Pennsylvanian fossil remains and process-based ecosystem modeling, providing support that ancient plants were functionally distinct from present-day analogs. Here, we incorporate experimentally and empirically constrained paleo plant functional types (PFTs; e.g., arborescent lycopsids, medullosans, cordaitaleans, and tree ferns) and biomes into a global climate model, Community Earth System Model, to simulate the response of terrestrial climate to Late Paleozoic plants under changing atmospheric CO₂, sea level, and ice volume. We compare the response of precipitation patterns, surface temperature, and continental runoff to extinct Pennsylvanian and modern vegetation distributions. Our preliminary results suggest that paleo-PFTs produce increased values of mean annual precipitation minus evaporation in low-latitude Pangaea and increased seasonality of surface temperatures in the southern mid-latitudes compared to modern-PFT analogs. This work highlights the importance of accounting for paleo-plant physiology in modeling vegetation-climate feedbacks during past intervals of climate change.