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

TLDR

Monthly SeaWiFS ocean‑colour data from September 1997 to May 2000 were used to estimate chlorophyll‑a around New Zealand, with the OC4v4 algorithm validated against in‑situ light‑field measurements and HPLC pigment concentrations. The OC4v4 algorithm accurately estimates chlorophyll‑a below 0.6 mg m⁻³ but overestimates higher concentrations; average chlorophyll‑a in the New Zealand EEZ ranged 0.26–0.43 mg m⁻³, with subtropical and Tasman Sea exhibiting spring‑autumn blooms, subantarctic waters showing a low‑magnitude autumn peak, the Subtropical Front having the highest chlorophyll, and warm‑core eddies along the east coast displaying low chlorophyll concentrations.

Abstract

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.