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The Miocene climate in New Zealand: Estimates from paleobotanical data

Mike Pole

Plain Language Abstract

Past estimates of New Zealand's Miocene climate have been made using a variety of evidence. These have ranged from using the current temperature requirements of marine invertebrates that have been found as fossils, to more complex estimates using stable isotope ratios in shells. More recently, techniques have been proposed to derive temperature and rainfall from 'foliar physiognomy,' that is, the size and shapes of leaves. At a very crude level, large leaves tend to indicate warm temperatures whereas many toothed leaves suggest cool temperatures. In detail, such relationships have been applied to assemblages of fossil leaves, and estimates of climate have been made to surprising levels of claimed precision. Such an approach is relatively independent of taxonomy in that the identity of the leaves does not need to be known, although in most cases, they still need to be partitioned into species. However, where taxa have been identified, these give another approach to determining climate. Essentially this is an independent check on the foliar physiognomy. Application of this method has become much easier due to the phenomenon of easily accessed databases of global plant distribution and cheap computing power. For virtually any modern plant taxon now, and many vertebrates, several climate variables that it encounters over its range can be determined. These results can be applied to fossils and their overlap can suggest past climate. Again, at a crude level, if a fossil assemblage contains two taxa, one limited to subtropical to tropical climates today, and another that extends from temperate to subtropical conditions today, finding them together as fossils would suggest the climate was subtropical.
This paper applies a range of foliar physiognomic techniques and the known climate ranges of identified taxa to quantify climate in the New Zealand Miocene. The results confirm previous estimates that early to earliest middle Miocene temperatures were much warmer than today (a Mean Annual Temperature of ca. 10°C). Mean annual temperatures were highly likely to have reached 17–18°C, and may well have achieved levels several degrees higher. However, plant fossil evidence that the climate was ever truly tropical, is absent.

The results are important, not only to help perfect global climate models, but to provide a cautionary note on the precision with which some results are given.

Resumen en Español

text

Traducción: Enrique Peñalver

Résumé en Français

Text

Translator: Kenny J. Travouillon

Deutsche Zusammenfassung

In progress

Translator: Eva Gebauer

Arabic

in progress

Translator: Ashraf M.T. Elewa

 

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