Observations on the horizontal coherence of chlorophyll a and temperature

Abstract

Time series of chlorophyll a fluorescence and temperature have been obtained at a number of depths, from two widely separated areas of the North Atlantic. These data strengthen the view of Platt and his co-workers that, over space scales between 40 m and 1 km, phytoplankton behaves as a passive contaminant of fluid motion. It was found that the observed high coherence between chlorophyll a and temperature extended to longer wavelengths for stations observed in temperature spring bloom conditions, than for stations observed in tropical summer conditions.

Certain features of the temperature and chlorophyll a power spectra are discussed which suggest that, at frequencies less than the Brunt-Va¨isa¨la¨frequency, internal waves make a significant con-contribution to the spectrum. This implies that, for space scales between tens of meters and a few kilometres, improved sampling methods will be required to separate the effect of internal waves from the real spatial heterogeneity of the phytoplankton.