Stratified and nonstratified areas in the North Sea: Long-term variability and biological and policy implications

The European Unions' Marine Strategy Framework Directive aims to limit anthropogenic influences in the marine environment. But marine ecosystems are characterized by high variability, and it is not trivial to define its natural state. Here, we use the physical environment as a basis for marine...

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Bibliographic Details
Published in:Journal of geophysical research. Oceans 2015-07, Vol.120 (7), p.4670-4686
Main Authors: van Leeuwen, Sonja, Tett, Paul, Mills, David, van der Molen, Johan
Format: Article
Language:English
Subjects:
Anthropogenic factors
Biological
Classification
ecohydrodynamics
Food chains
Food webs
Foods
Geophysics
hindcast
Marine
Marine ecosystems
Marine environment
North Sea
phytoplankton
Plankton
Policies
Stratification
Webs
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Summary:The European Unions' Marine Strategy Framework Directive aims to limit anthropogenic influences in the marine environment. But marine ecosystems are characterized by high variability, and it is not trivial to define its natural state. Here, we use the physical environment as a basis for marine classification, as it determines the conditions in which organisms must operate to survive and thrive locally. We present a delineation of the North Sea into five distinct regimes, based on multidecadal stratification characteristics. Results are based on a 51 year simulation of the region using the coupled hydrobiogeochemical model GETM‐ERSEM‐BFM. The five identified regimes are: permanently stratified, seasonally stratified, intermittently stratified, permanently mixed, and Region Of Freshwater Influence (ROFI). The areas characterized by these regimes show some interannual variation in geographical coverage, but are overall remarkable stable features within the North Sea. Results also show that 29% of North Sea waters fail to classify as one of the defined stratification regimes, due to high interannual variability. Biological characteristics of these regimes differ from diatom‐based food webs in areas with prolonged stratification to Phaeocystis‐dominated food webs in areas experiencing short‐lived or no stratification. The spatial stability of the identified regimes indicates that carefully selected monitoring locations can be used to represent a substantive area of the North Sea. Key Points: The North Sea can be delineated into five distinct stratification regimes These regimes show remarkably stable spatial occurrence 29% of the area defies classification due to high interannual variability
ISSN:2169-9275
2169-9291
DOI:10.1002/2014JC010485