Optical properties of the coastal and oceanic waters off South Island, New Zealand: Regional variation

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Abstract
A study of the optical properties of the varied water masses in inshore and oceanic waters around the South Island of New Zealand was made. This was a contribution to a larger effort to model the productivity of the southern sector of New Zealand's Exclusive Economic Zone. A combination of spectroradiometry, PAR sensor deployments, transmissometry, and yellow‐substance measurement was used at 30 stations to characterise the optical properties of the region. The waters were classified according to Jerlov's system for ocean waters. Inshore sites on the west and east coasts and Foveaux Strait fell into optical types Coastal I and Oceanic III. Oceanic II waters occurred in the Subtropical Convergence Zone (STCZ). Subantarctic waters and those south of the STCZ were in the clear categories Oceanic I and IB. Attenuation coefficients (K) varied more than three‐fold from 0.05 to 0.16 m−1. Reflectance was lowest off the Fiordland coast where light‐absorbing yellow substance was maximal. An index of the average lighting of the mixed layer (Eo ) for phytoplankton photosynthesis was calculated from the light‐depth profile. Highly varying mixed‐layer depths, combined with a 3‐fold difference in K, caused Eo to vary by as much as 11, suggesting that the growth of oceanic phytoplankton in the region may vary far more than predicted by present models.