A modelling study of Emiliania huxleyi in the NE atlantic

Intensive (> 10,000 cells ml−1) and extensive (> 100,000 km2) blooms of the coccolithophorid Emiliania huxleyi frequently occur in the NE Atlantic, usually in the months of June and July, and only north of 50°N. This article describes a modelling study of these blooms, with the aim of understanding why they occur. That is to say, which water conditions allow Emiliania huxleyi to become dominant amongst the phytoplankton? Providing answers to these questions in the NE Atlantic, and comparing the results with data from other areas, allows us to tackle the question: what is the ecological niche for Emiliania huxleyi? The model described in this article is a single-layer ID Eulerian phytoplankton seasonal succession model, with detailed representations of physical, chemical and biological forcing functions and interactions. Model assumptions and their derivation from data are described, and sensitivity analyses examine the reliance of model results on individual assumptions. The model results suggest that, in the summer of 1991 in the NE Atlantic, the most likely factors causing the bloom of Emiliania huxleyi were high light (high surface irradiances, shallow stratification) and low phosphate (phosphate limiting rather than nitrate). The model was able to reproduce the observed distributoin of Emiliania huxleyi in the NE Atlantic by assuming that Emiliania huxleyi has similar limitations to other phytoplankton species except that it possesses a competitive advantage at high light and low phosphate.