The Miocene climate in New Zealand: Estimates from paleobotanical data

Abstract

Miocene New Zealand was a small, highly oceanic landmass which makes it ideal for recording terrestrial climate, free of the complications of a continental setting. Fortunately, it has a good Miocene fossil record, both marine and terrestrial. This paper reviews past conclusions about Miocene climate then attempts to derive some key climate indices for the period using a variety of plant fossil proxies. The paper looks at three slices of Miocene time-a broad early to earliest middle Miocene time, a restricted period in the middle Miocene, and broader middle-late Miocene. The results suggest early to earliest middle Miocene Mean Annual Temperatures (MATs) reached at least 17-18°C, thus, about 6-7°C warmer than today (coastal areas of southern New Zealand today have a MAT of about 11°C). At times Miocene MAT may have reached 19-20°C. These figures support the cooler estimates of New Zealand Miocene climate that have been made previously by using palebotanical proxies, rather than those based on marine invertebrates. Based on plant fossils there is no evidence that New Zealand ever reached truly 'tropical' (i.e., megathermal) conditions (> 24-25°C). The climate in the middle Miocene is confounded by signs of precipitation and temperature change, and the rarity of leaf fossils. However, the data suggest both cooling and drying from the early Miocene. The presence of crocodiles yet the disappearance of palms, suggests a MAT that was at the lower end of existence for both of these groups, perhaps about 14°C. By the late Miocene, there is evidence for significant cooling, both from leaf size and a drop in plant diversity, which resulted in vegetation dominated in many places by Nothofagus. © Palaeontological Association July 2014.