Testing the synchroneity of pollen signals using tephrostratigraphy

Since the advent of radiocarbon dating, the concept of synchronous pollen-vegetation events extending across broad regions such as the British Isles, which had emerged from earlier pollen-stratigraphic studies, has been largely refuted. Nevertheless the assumption that pollen profiles within a geographically coherent area should exhibit broadly comparable and synchronous pollen signals still holds currency among some palynologists. This assumption is tested here by comparing pollen spectra between lateglacial and postglacial sites in northern New Zealand, until recently unaffected by human activity, where independent correlations are obtained by tephrochronology. At sites of similar size, morphology, and depositional environment within the same phytogeomorphic region, it is possible to achieve accurate palynological correlations, provided local taxa and those representing ecologically disparate source species are omitted from the pollen datasets. However, anomalous correlations may still occur and are more likely when sites with different depositional environments or at greater distances are compared. These results suggest that the concept of synchronous pollen signals, even between nearby sites with similar depositional setting, is not universally applicable and it is possible that erroneous palynostratigraphic correlations have been made in the past.