A Late Miocene Cold Spell in Zealandia: Evidence From the Whitianga Group, Coromandel, New Zealand

Abstract

Cooling of Zealandia in the late Miocene occurred because of northward movement of the Antarctic Circumpolar Current, gradually pushing Zealandia out of a subtropical warm pool. In addition, uplift of the Southern Alps and global cooling resulted in the emergence of temperate ecosystems present in New Zealand today. Terrestrial paleoclimate reconstructions of Zealandia from this pivotal transitional period, however, are rare. The Kaimarama flora from the Coromandel Peninsula, New Zealand, presents a glimpse into the vegetation and climate of middle Zealandia during the late Miocene (Tortonian, 10.4 ± 1.2 Ma). The reconstructed temperature is cooler than today (mean annual temperature = 11.4 ± 2.4°C vs. 14°–15°C, respectively). This finding is notable because other marine and terrestrial paleoclimate records from the area do not indicate similarly cool conditions until at least 3 million years later. Reconstructed precipitation and productivity of the Kaimarama flora are similar to that of the Coromandel Peninsula today, with precipitation of >150 cm yr ⁻¹ , moderate precipitation seasonality (driest month precipitation is 40% of mean monthly precipitation), and high productivity (net primary productivity of ∼1.4 kgC m ⁻² yr ⁻¹ ) likely sustained by near year‐round growing temperatures (coldest quarter temperature >5°C). The vegetation assemblage is unusual, as it is dominated by Phyllocladus (Podocarpaceae), which, in combination with ignimbrite that the Kaimarama lake deposit was found in, and Cyathea ‐dominated palynoflora, suggests that this vegetation reflects localized mid‐to‐late successional vegetation in a topographically variable volcanic terrane where rhyolitic eruptions and pyroclastic flows may periodically have denudated the landscape.