Environmental change during the Last Glacial Maximum (c. 25,000-c. 16,500 years B.P.) at Mt Richmond, Auckland Isthmus, New Zealand

Abstract

A 2 m section at the base of Mt Richmond contains a palynological record of the last glacial maximum (LGM) (c. 25 000–c. 16 500 14C years BP) vegetation of the Auckland Isthmus. Three silicic tephra layers derived from the Taupo Volcanic Centre (Okaia Tephra c. 23 500 14C years BP, Kawakawa Tephra c. 22 500 14C years BP) and the Okataina Volcanic Centre (Okareka Tephra c. 18 000 14C years BP), both centres lying within the Taupo Volcanic Zone, provide the basis of the chronology supported by radiocarbon dates. The pollen diagram is divided into two pollen zones separated by the deposition of a locally derived basaltic ash.

From c. 25 000–23 000 14C years BP the site was initially a eutrophic lake fringed by Leptospermum and Typha, which altered to a Cyperaceae/Leptospermum-dominated swamp. The regional vegetation at the time was beech-dominated forest; canopy conifers were present but formed a minor part of the local forest.

From c. 23 000–16 500 14C years BP regional forest was further restricted to local patches in extensive shrubland/grassland. Temperatures may have been depressed by more than 4–5°C. The eruption of a local volcano dammed the swamp outlet resulting in a return to lacustrine conditions. Local volcanism may have accelerated vegetation change already under way as a result of climate change to cooler conditions. This record provides a view of LGM vegetation of the Auckland Isthmus and a template for earlier cold stages of the Quaternary.

Keywords

Rhyolitic tephra, palynology, climate change, tephrostratigraphy, last glacial maximum, Auckland Isthmus.