Environmental Geology & Geochemistry Seminar (EGGS) Lecture Series

Thu, Nov 14, 2019, 12:30 pm to 1:20 pm
Guyot 220

Reconstructions of past atmospheric CO2 are critically important for understanding the Earth’s climate sensitivity to this important greenhouse gas. The Miocene has long presented a conundrum because most estimates of past atmospheric CO2 for this time interval are similar to
preindustrial values (~300ppm), and are therefore too low to maintain the elevated Miocene global temperatures inferred from the geologic record. I will present new atmospheric CO2 estimates developed from fossilized leaves of an Early Miocene rainforest ecosystem. The fossil leaves are exquisitely preserved in an annually laminated diatomite deposit from the Foulden Maar on the South Island of New Zealand; an ancient crater lake into which sediments accumulated during a 100,000-yr interval at the Oligocene-Miocene boundary (~23 million years ago). Using gas exchange modeling that takes into consideration leaf taxonomy, anatomical measurements, and carbon isotope composition we developed a record of atmospheric CO2, carbon assimilation rates, and plant water-use efficiency for this Early Miocene ecosystem based on 72 organically preserved leaves representing 18 different plant species. The new data provide CO2 estimates of 450-550ppm, in line with our current understanding of CO2 climate sensitivity and provide empirical evidence for enhanced water-use efficiency and increased terrestrial biosphere productivity in a warmer CO2-enriched world. I’ll also discuss two lipid-based paleoclimate records (leaf wax dD and GDGT-inferred temperature) from the Foulden Maar sedimentary sequence.