Distribution of organic-walled marine and terrestrial palynomorphs in surface sediments, offshore eastern New Zealand

Abstract

Organic-walled dinoflagellate cyst (dinocyst) and terrestrial spore/pollen assemblages are analysed from 38 modern surface sediments offshore eastern New Zealand, from 33 to 54°S, water depths of 79 to 4680 m, and spanning the prominent Chatham Rise. The most diverse, abundant and best preserved marine and terrestrial assemblages are observed on the northern flank of Chatham Rise, coincident with the Subtropical Front region being an area of enhanced biological activity and primary productivity. Dinocyst assemblages are dominated by the gonyaulacoid (autotrophic) taxa Impagidinium, Nematospheropsis labyrinthus, Operculodinium centrocarpum, Spiniferites and peridinioid (heterotrophic) Brigantedinium. Taxa with preferences for cooler (e.g., Selenopemphix antarctica) and warmer (e.g., Impagidinium strialatum) water masses are identified in distribution records and canonical correspondence analysis. Of the nine environmental parameters measured, dinocyst assemblages were strongly correlated to sea-surface temperature (February) and chlorophyll a (autumn). Terrestrial spores and pollen dominate palynomorph assemblages in many sites, and primarily reflect the presence of lowland podocarp-broadleaf forest of onshore eastern New Zealand. Spores and bisaccate pollen dominate assemblages, with angiosperm pollen comprising up to 10% in the Chatham Rise area. Pollen from plants restricted to northern regions has been transported south via subtropical surface currents. This pilot study shows that palynomorph assemblages offshore New Zealand, including the high terrigenous input margin of eastern North Island, can provide suitable proxy records for characterisation of coeval marine and terrestrial changes through time.