A Tortonian (Late Miocene, 11.61–7.25Ma) global vegetation reconstruction

Abstract: For the Tortonian age of the Miocene Epoch (11.6–7.25Ma) we present a global palaeobotanical and palaeoecologically-based vegetation dataset, combined with a best-fit Late Miocene climate-vegetation model experiment to create an advanced global data–model hybrid biome reconstruction. This new palaeoecological database and global vegetation reconstruction can be used both for the purposes of validating future palaeoclimate model simulations, as well as a land cover dataset to initialise palaeoclimate modelling experiments. Our Tortonian reconstruction shows significant changes in the distribution of vegetation compared to modern natural vegetation. For example in contrast to the modern scenario in the Northern Hemisphere, boreal forests reached 80°N and temperate forests were present above 60°N. Warm–temperate forests covered much of Europe, coastal North America and South-East Asia. Our reconstruction shows a spread of temperate savanna in central USA, the Middle East and on the Tibetan Plateau. Evidence for arid deserts is sparse, with the exception of the Atacama region (South America). Areas that exhibit arid desert today in the Tortonian were instead covered by shrublands, grasslands, savannas and woodlands. The extent of tropical forests in South America was likely reduced but expanded in the Indian sub-continent and East Africa. This pattern of global vegetation in the Late Miocene suggests a warmer and wetter world, which is supported by the pattern of climate anomalies predicted by our best-fit palaeoclimate-vegetation model experiment. Global mean annual temperature may have been as much as 4.5°C higher than present day with many regions experiencing higher than modern amounts of precipitation over the annual cycle. The pattern of temperature and precipitation change reconstructed palaeobotanically, and predicted within our climate model experiment, infers a global forcing agent on Tortonian climate (e.g. such as elevated concentrations of greenhouse gases) to explain the observed and modelled climate anomalies. This is in contrast to current proxy records of Tortonian atmospheric CO2 which range from Last Glacial Maximum to mid-20th Century levels. [Copyright &y& Elsevier]