Uptake of nitrate and ammonium, and distribution of related variables, in the upwelled plume of western cook strait/taranaki bight, new zealand

Abstract

To distinguish the manner of spread of upwelling effects in the Cook Strait/Taranaki Bight (New Zealand) region, nitrogen uptake and the distribution of nutrients and chlorophyll a are described. NO3 concentrations were closely linked to upwelled water, but this was distributed irregularly and not necessarily with the upwelling focus. NH4, SRP, and chlorophyll a showed varying degrees of association with recycling processes, but linear correlations were not present. NO3 uptake was strongly inhibited by ambient NH4, but not completely. There was no evidence of either N or P limitation of total planktonic biomass, and there was indirect evidence from C/N uptake and cellular ratios that a high growth rate prevailed. N uptake increased with irradiance (= decreasing depth) similar to photosynthesis, but without high light inhibition, and could be related to light by a simple equation. The irregularity of distribution of features suggests that future modelling of the phytoplankton biomass in the region could benefit from analysis of event occurrence rather than of evenly progressive changes. © Crown copyright 1988.