The spatial and temporal development of the spring bloom during the JGOFS North Atlantic Bloom Experiment, 1989

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Abstract
The south to north development of the spring bloom in the North Atlantic Ocean was observed during four cruises from April to August 1989. Transects with towed undulating instrumentation packages and CTD profiles on station were made between 42°N and 54°N, along 17°W and 20°W in April and between 47°N and 60°N along 20°N in May, June and July/August, giving vertical sections of temperature and chlorophyll concentration derived from in vivo fluorescence. These sections show the relationship between the onset of seasonal stratification and the initiation of the spring bloom. Supporting data from microscopic analysis of the major phytoplankton species show that the seasonal succession commenced with diatoms, followed in turn by coccolithophores, flagellates and dinoflagellates. During the development of summer stratification the mesoscale distribution of chlorophyll was strongly determined by the depth of the mixed layer, but once stratification had been firmly established higher chlorophyll values tended to be found within the warmer eddies (meanders). One possible explanation of this result is that phytoplankton growth is higher in the warmer eddies.