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The role of turbulence in fueling the subsurface chlorophyll maximum in tidally dominated shelf seas
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  • Johannes Becherer,
  • Hans Burchard,
  • Jeffrey Richard Carpenter,
  • Ulf Gräwe,
  • Lucas Merckelbach
Johannes Becherer
Helmholtz-Zentrum Hereon

Corresponding Author:johannes.becherer@hereon.de

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Hans Burchard
Leibniz Institiute for Baltic Sea Research Warnemünde
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Jeffrey Richard Carpenter
Helmholtz-Zentrum Hereon
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Ulf Gräwe
Leibniz Institute for Baltic Sea Research Warnemünde
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Lucas Merckelbach
Helmholtz-Center Hereon
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Glider observations show a subsurface chlorophyll maximum (SCM) at the base of the seasonal pycnocline (PCB) in the central North Sea during stable summer conditions. A co-located peak in the dissipation rate of turbulent kinetic energy suggests the presence of active turbulence that generates the nutrient fluxes necessary to fuel the SCM. A one-dimensional turbulence closure model is used to investigate the dynamics behind this local maximum in turbulent dissipation at the PCB as well as its associated nutrient fluxes. Based on a number of increasingly idealized forcing setups of the model, we are able to draw the following conclusions: (1) only turbulence generated inside the stratified PCB is able to entrain nutrients from the bottom mixed layer into the SCM region; (2) surface wind forcing only plays a secondary role during stable summer conditions; (3) interfacial shear from the tide accounts for the majority of turbulence production at the PCB; (4) in stable summer conditions the strength of the turbulent nutrient fluxes at the PCB is set by the strength of the anticyclonic component of the tidal currents.