Publication Date:
2009-05-13
Description:
Phytoplankton blooms are a recurring phenomenon that have significant impact on annual biogeochemistry and food-web dynamics in many aquatic ecosystems. The causes for their variability, which is high especially in coastal seas, remain poorly understood. We present an example for distinct differences in the spatio-temporal chlorophyll-a (CHL-a) distribution on an interannual scale, integrating high-frequency data from an autonomous measuring device (FerryBox), which operated on an alongshore route in the coastal North Sea. While in one year CHL-a was spatially homogeneous (2004), a bloom only developed in one part of the transect in the following spring period (2005). In this study, we use a one-dimensional Lagrangian particle tracking model, which operates along the mean current direction, combined with a NPZ-model to identify the mechanisms controlling interannual bloom variability on an alongshore transect. The model results clearly indicate that in 2004, the local light climate triggered phytoplankton growth, whereas in the following year, advective transport determined the spatial structure of the spring bloom. A pronounced eastward inflow event in 2005 imported a high CHL-a patch into the western half of the study area from the adjacent Southern Bight. It did, however, not last long enough to also spread the bloom into the eastern part, where high turbidity prevented local phytoplankton growth. The model identified two interacting mechanisms, light climate and hydrodynamics that control the alongshore dynamics. Especially the occurrence of a pronounced spring bloom despite unfavourable light conditions in 2005 underlines the need to carefully consider hydrodynamics to understand ecosystem functioning in coastal environments.
Print ISSN:
1810-6277
Electronic ISSN:
1810-6285
Topics:
Biology
,
Geosciences
Permalink
