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

Abstract

Ocean colour data from the NASA Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) was used to estimate chlorophyll a concentration around New Zealand on a monthly basis between September 1997 and May 2000. The performance of the SeaWiFS chlorophyll a algorithm (OC4v4) was investigated by comparing in situ measurements of the underwater light field with measurements of phytoplankton pigment concentration by High Performance Liquid Chromatography. The 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 region 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 Tasman Sea waters had a classical cycle of spring and autumn chlorophyll blooms consistent with production being co‐limited by nitrate and light. Subantarctic waters had a low‐magnitude annual cycle of chlorophyll abundance that peaked in early autumn, consistent with production being predominantly limited by a combination of iron and light. Chlorophyll was generally highest in the Subtropical Front where subtropical and subantarctic waters mix. A series of persistent warm‐core eddies along New Zealand's east coast was obvious in many images, manifest as regions of low chlorophyll concentration.