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.Mike Pole. Queensland Herbarium, Brisbane Botanic Gardens Mt Coot-tha,

Five new species of Corybas (Diurideae, Orchidaceae) endemic to New Zealand and phylogeny of the Nematoceras clade

“…Corysanthes, and dispersed to NZ about 8 Myr ago (late Miocene). This was a time of significant climatic and geological changes in NZ; the temperature dropped, rainfall increased, uplift that would later create the NZ Alps began and cool-temperate elements such as southern beech dominated much of the vegetation (Fleming 1962, Heenan & McGlone 2013, Poole 2014. Nowadays, it is in the understory of these beech forests where many of these orchids grow, especially those within the C. trilobus aggregate.…”

The formation of the oceanic temperate forests of New Zealand

“…Zealand forests (Reichgelt et al 2013(Reichgelt et al , 2015Pole 2014;Conran et al 2015b). Similar advances in southern South American, Australian and Antarctic palaeobiogeography are developing a comprehensive overview of the floristic evolution of the southern end of the world (Kooyman et al 2014).…”

“…Outline of geological time scale (Raine et al 2015) and geological and climatic change (Lee et al 2001;McGlone 2006;Pole 2014 (Table 2). An application of this scheme to the humid lowland areas of New Zealand places most lowland associations as warm temperate moist to wet forest with cool temperate moist to wet forests occurring below the mean annual temperature (MAT) 12°C isotherm.…”

“…Of the tree genera recorded there, 32 are extant in New Zealand lowland forests ). In the mid Miocene, from about 14 Ma, a number of taxa prominent in Australia (Acacia, Casuarina, Eucalyptus, Gyrostemonaceae) became abundant at New Zealand sites, a change that has been linked to the climate becoming somewhat cooler and seasonally drier than previously, and subject to frequent fire (Mildenhall & Pocknall 1989;Pole 2003Pole , 2014. By the late Miocene these 'Australian' groups began to disappear (see next section).…”

“…Firerelated traits are of great antiquity in the Australian flora (Crisp & Cook 2013) and the presence in New Zealand over the Miocene period of taxa now abundant in fire-prone vegetation in Australia such as Acacia, Casuarinaceae, Eucalyptus, Gyrostemonaceae and Proteaceae (Mildenhall & Pocknall 1989;Lee et al 2010) in association with charcoal-rich deposits argues for a fire-adapted flora. Pole (2003Pole ( , 2014 suggested that even during the warm, wet, early Miocene fire-prone palm swamps existed and he has argued that the middle Miocene became cooler and drier and that fire-prone communities dominated by Eucalyptus and Casuarinaceae spread, perhaps in response to a poleward movement of the subtropical high-pressure belt. Lack of natural fire in contemporary New Zealand is due largely to a lack of ignition as the extreme oceanicity results in a low frequency of lighting-producing thermal heating in the interior (Perry et al 2014).…”