Millimetre-scale pollen analysis of non-varved lacustrine sediments from Onepoto maar palaeolake, Auckland, reveals distal vegetation responses and landscape recovery following the ∼25.5-ka Oruanui supereruption, New Zealand

The similar to 25.5-ka Oruanui supereruption (Taupo volcano, New Zealand) erupted >1100 km(3) of pyroclastic material during the Last Glacial Maximum. The impacts of this event on climate and the New Zealand environment remain unresolved, particularly on ecological timescales. Using sediment cores from Onepoto maar palaeolake, Auckland (similar to 240 km upwind from source), we have analysed pollen assemblages at contiguous 1-mm intervals, around an intact 3-cm layer of the Kawakawa-Oruanui Tephra to resolve and assess post-eruption vegetation impacts and landscape recovery. Sediments immediately above the tephra record a decline in the relative abundance of the dominant canopy species of Fuscospora, and concurrent increase in the abundances of grasses, herbs, ferns and shrubs. These changes reflect a brief (<10 years) part-defoliation of canopy trees, permitting more light to penetrate and to encourage sub-canopy vegetation growth. A short-lived volcanogenic cooling inferred from Antarctic ice core records may have contributed to the changes but cannot be separated from the immediate and direct ecological impacts of ashfall on vegetation following the eruption. Our results, here applied to the world's most recent supereruption, more generally demonstrate the value of millimetre-scale stratigraphic pollen analysis from non-varved lacustrine sediments as a tool for assessing past eruptive impacts on sub-decadal timescales.