Phytoplankton distributions around New Zealand derived from SeaWiFS remotely-sensed ocean colour data

Ocean colour data from the NASA Sea-viewing Wide Field-of-view Sensor (SeaW iFS) was used to estimate chlorophyll a concentration around New Zealand on a monthly basis between September 1997 and May 2000. The performance of th e SeaWiFS chlorophyll a algorithm (OC4v4) was investigated by comparing in situ measurements of the underwater light field with measurements of phytop lankton pigment concentration by High Performance Liquid Chromatography. Th e algorithm performed well for chlorophyll a concentrations below 0.6 mg m( -3) but overestimated by a factor of two or more at higher concentrations. The average chlorophyll a concentration for New Zealand Exclusive Economic Zone was calculated as an indication of the overall productivity of the reg ion and varied between 0.26 and 0.43 mg m(-3) with no obvious relationship to the Southern Oscillation Index. New Zealand northern subtropical and Tas man Sea waters had a classical cycle of spring and autumn chlorophyll bloom s consistent with production being co-limited by nitrate and light. Subanta retic waters had a low-magnitude annual cycle of chlorophyll abundance that peaked in early autumn, consistent with production being predominantly lim ited by a combination of iron and light. Chlorophyll was generally highest in the Subtropical Front where subtropical and subantarctic waters mix. A s eries of persistent warm-core eddies along New Zealand's east coast was obv ious in many images, manifest as regions of low chlorophyll concentration.