EARLY TO MID HOLOCENE POLLEN SAMPLES CONTAINING MANGROVE POLLEN FROM SPONGE BAY, EAST-COAST, NORTH-ISLAND, NEW-ZEALAND

Mangroves (Avicennia marina var. resinifera (Forst.f.) Bakh.) lived in the Poverty Bay-East Cape region during the early to mid Holocene for about 4,000 years, from c. 9,800-6,000 years BP. This suggests an essentially frost-free climate at least one degree warmer than the present day, as required to allow germination and growth of Avicennia seedlings. Sea levels were then lower which would have provided a suitable substrate for the plants on the continental shelf, the local extinction of Avicennia was due to the combination of subsequent sea level rise, increased frostiness, and the disappearance of habitat. Pollen samples from four localities on the east coast of the North Island were examined, and all contain abundant evidence of recycled pollen from Cretaceous and Cenozoic sediments. Several samples from one locality (Sponge Bay, near Gisborne, about 7 km southeast of the only previously known North Island east coast early Holocene record of Avicennia) contain Avicennia pollen. Precise paleoclimatic studies were hampered by a massive influx of modem pollen into many of the samples, possibly caused by unrecognised modem cut and fill, recycling of the sediments, and hydrostatic injection of spore- and pollen-bearing water into the soft Holocene sediments under the pressure of the frequent flood conditions. However, radiocarbon dates are internally consistent, suggesting that the last-named is probably the prime cause.