Mixed diatom floras in sedimentary deposits from the 2016 Kaikōura Tsunami at Little Pigeon Bay, Aotearoa-New Zealand

Abstract

Abstract This study records the diatom flora from sedimentary deposits found within a coastal cottage, following the November 2016 Kaikōura earthquake and tsunami at Little Pigeon Bay, Banks Peninsula, Aotearoa-New Zealand. Unlike previous studies of diatoms from modern tsunami deposits, the sediments in this study were isolated from any previous (and subsequent) reworking of sediments. The diatom flora (n = 117 taxa) are dominated by benthic and planktonic lifeforms with preferences for marine (28%), brackish-marine (25%), fresh-brackish (19%) and fresh-water (17%) conditions. The higher abundances of benthic marine and brackish-marine diatoms are attributed to direct in-washing and reworking of open ocean-water with sandy marine sediments from the sub-tidal and inter-tidal zones. Comparatively high percentage counts of benthic fresh-brackish and freshwater diatom taxa also indicate significant freshwater sources and sediments from the stream and land adjacent to the cottage. Fractured and damaged diatom frustules within the flora, including broken sponge spicules, emphasise dynamic processes of reworking, abrasion and erosion during incoming and outgoing tsunami waves. Likelihood-based ordination analysis of the diatom flora indicates statistical differences between the flora in the back area of the cottage and the centre and front areas which we attribute primarily to the influence of different waves that inundated the cottage from the seaward and landward directions. Such a record affirms a highly mixed diatom flora from multiple sources and habitats. It also offers a first modern analogue from Aotearoa-New Zealand to assist future assessments of multi-proxy-based records of past tsunami events preserved in the geological record.