Plant wax reconstructions of Pliocene vegetation and hydroclimate – from scientific ocean drilling

Dual measurements of the carbon and hydrogen isotopic composition of plant wax, provide a powerful means to gather parallel evidence on vegetation and climate change. Following the Miocene expansion of C4 grasslands in the tropics, both C3 and C4 plant types are present on the tropical landscape. Carbon isotopes in plants can reveal the history of vegetation during the Pliocene. Hydrogen isotopes in plants record that of precipitation isotopes, tracing rainout processes associated with large scale atmospheric circulation patterns. Drilling by the International Ocean Discovery Program and earlier scientific ocean drilling has recovered Pliocene age sediments, around the margins of Africa and South Asia, capturing plant waxes that blow off or are washed off the continents by fluvial transport. Multiple drill cores have published plant wax C and H isotopic reconstructions available, that I synthesize here to explore the regional expression of Pliocene vegetation and climate. This effort seeks to address the IODP Science Plan: how does climate respond to elevated CO₂ (challenge 1), what drives past precipitation change (challenge 3) and vegetation response (challenge 7)? It contributes to the flagship initiative of the IODP 2050 Science Framework to ground-truth climate models, focused on the critical aspect of assessing precipitation patterns on land across elevated CO₂ to validate model reconstructions of past hydrological change and thus to constrain confidence in future predictions. To achieve the model connection, the hydrogen isotope data are summarized for comparison to isotope-enabled climate model output, including General Circulation Climate model experiments for the 3.2 Ma focus of the Pliocene Model Intercomparison Project (PlioMIP) and 5-4 Ma timeslice – see  presentation by Knapp et al., (this conference).