Orbitally-influenced vegetation record of the Mid-Pleistocene Climate Transition, offshore eastern New Zealand (ODP Leg 181, Site 1123)

摘要

A census of Plio-Pleistocene (5-0 Ma) terrestrial palynomorph assemblages from ODP Site 1123, located 1100 km offshore eastern New Zealand and in a water depth of 3290 m, reveals marked variations in warm- (Cyathea, tall tree Podocarpus/Prumnopitys, Dacrydium cupressinum) and cold- (Halocarpus, Phyllocladus, Nothofagus fusca type, Coprosma) climate indicator species at Milankovitch-scale periodicities. Time series analysis indicates that the vegetation record is covariant with marine climate proxies (carbonate content) and is strongly coherent at the 40-ka and 100-ka orbital frequency. A pronounced increase in amplitude and a coeval decrease in frequency of climate cycles from 40 to 100 ka occurs between 0.92 and 0.62 Ma, and provides a rare vegetation record of a fundamental reorganisation of Earth's climate system the Mid-Pleistocene Climate Transition. Despite the long distance from land and great water depth, terrestrial palynomorphs are relatively abundant in this high-resolution marine sediment record, where they reflect a southern North Island source. The predominance of robust spores and buoyant pollen (Cyathea, Podocarpus/Prumnopitys) indicates considerable current sorting and degradation of more delicate morphotypes during transport across the eastern North Island shelf. Little evidence is found for sorting and transport processes being significantly modulated by climate.