MEPS 335:57-68 (2007)  -  doi:10.3354/meps335057

Short-term changes in chlorophyll distribution in response to a moving storm: a modelling study

Yongsheng Wu1,*, Trevor Platt1, Charles C. L. Tang1, Shubha Sathyendranath1,2

1Coastal Ocean Science, Bedford Institute of Oceanography, Dartmouth, Nova Scotia B2Y 4A2, Canada
2Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth PL1 3DH, UK

ABSTRACT: Using a 3-D ocean circulation model of the Labrador Sea, we investigated the immediate response, through vertical redistribution of the chlorophyll field, to a steadily moving storm. The model is forced by a prescribed wind and pressure field. The numerical experiments included a control run to analyze the horizontal and vertical structure of the chlorophyll field, and several sensitivity runs to investigate the response to changes in the storm parameters (translation speed, size and intensity) and the seasonal distribution of chlorophyll. The model results showed that after the passage of the storm, surface chlorophyll in the Labrador Sea is generally increased by vertical mixing. The largest increase occurs in autumn. In summer (control run), the surface chlorophyll concentration is 1 to 3 mg m–3 higher than the concentration before the storm in almost all the areas under the influence of the storm. In the shelf regions, however, the increase is very small. The changes in surface chlorophyll concentration are shown to be primarily controlled by the mixed-layer depth and the initial chlorophyll distribution. Nitrate brought from the deep reservoir to the mixed layer by entrainment was estimated from the model. For a typical storm in summer, 3.35 × 103 mol of new nitrate is added to the mixed layer for each km of storm track. Primary production rates following the introduction of new nitrate will contribute to further change in surface chlorophyll, but on a longer time scale.

KEY WORDS: Moving storm · Chlorophyll · Vertical distribution · 3-D model

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