PB-210 CHRONOLOGY FROM WELLINGTON HARBOR, NEW-ZEALAND

A sediment accumulation record based on the levels of ''unsupported'' Pb-210 was obtained from a core taken from the centre of Wellington Ha rbour, New Zealand. Sediment accumulation rates (SARs) varied from 3 t o 5 mm yr(-1). Before 1920, SARs were sufficiently high to dilute unsu pported levels of Pb-210 to background, but had fallen below the mean by 1925 maintaining constant SARs until 1953. These data provide a hig her resolution chronology of early 20th century SARs than was previous ly available. Comparison with Cs-137 data confirms that there was a si gnificant increase in SARs between 1953 and 1967, but that these have remained fairly constant since 1974. Data from the two radionuclides a re consistent after 1974, and Pb-210 data are consistent with other ch ronological measurements before 1953. Therefore, it is suggested that the two radionuclides are immobile in the marine sediments of Wellingt on Harbour and that differences between the two SARs are real.