Abstract :
A one-dimensional 1D. coupled physical–microbiological model has been applied to a site in the central North Sea. The
impact of the choice of the turbulence closure scheme on the modelling the primary production has been investigated.
The model was run with four different parameterisations of vertical mixing of heat, momentum and dissolved and
suspended matters, using M2 tidal forcing and the hourly mean meteorological forcing of 1989 to reproduce the annual
thermal structure and primary production. The four mixing parameterisations are: Level 2 turbulence closure scheme
wMellor, G.L., Yamada, T., 1974. A hierarchy of turbulence closure models for planetary boundary layers. J. Atmos. Sci. 31,
1791–1806; Mellor, G.L., Yamada, T., 1982. Development of a turbulence closure model for geophysical Fluid problems.
Rev. Geophys. Space Phys. 20 4. 851–875x using an explicit numerical scheme wSharples, J., Tett, P., 1994. Modelling the
effect of physical variability on the midwater chlorophyll maximum. J. Mar. Res. 52, 219–238x; a version of the Level 2.5
turbulence closure scheme wGalperin, B., Kantha, L.H., Hassid, S., Rosati, A., 1988. A quasi-equilibrium turbulent energy
model for geophysical flows. J. Atmos. Sci. 45, 55–62; Ruddick, K.G., Deleersnijder, E., Luyten, P.J., Ozer, J., 1995.
Haline stratification in the rhinermeuse freshwater plume: a 3D model sensitivity analysis. Cont. Shelf Res. 15 13.
1597–1630x simplified to use an algebraic mixing length by Sharples and Simpson wSharples, J., Simpson, J.H., 1995.
Semidiurnal and longer period stability cycles in the Liverpool Bay region of freshwater influence. Cont. Shelf Res. 15,
295–313x, also solved explicitly; the same simplified L2.5 scheme with an implicit numerical solution and modified vertical
discretisation scheme wAnnan, J.D., 1999. Numerical methods for the solution of the turbulence energy equations in the shelf
seas. Int. J. Numer. Methods Fluids 29, 193–206x; and another version of the same scheme but using a different algebraic
mixing length. as described by Xing and Davies wXing, J., Davies, A.M., 1996a. Application of turbulence energy models to
the computation of tidal currents and mixing intensities in the shelf edge regions. J. Phys. Oceanogr. 26, 417–447; Xing, J.,
Davies, A.M., 1996b. Application of a range of turbulence models to the computation of tidal currents and mixing intensities
in shelf edge regions. Cont. Shelf. Res. 16, 517–547; Xing, J., Davies, A.M., 1998. Application of a range of turbulence
energy models to the computation of the internal tide. Int. J. Numer. Methods Fluids 26, 1055–1084x. Various model outputs
at the sea surface and in depth profiles have been compared with data collected in 1989 as part of the North Sea Project
wHuthnance, J.M., 1990. Progress on North Sea Project. NERC News, vol. 12, pp. 25–29, UKx. It is shown that the biological results are extremely sensitive to the small changes in the physical conditions, which arise due to the different
turbulence schemes tested. The timing of the spring bloom and the maintenance of the midwater chlorophyll maximum all
differ greatly between model runs, and the gross primary production varies by a factor of two from the highest to lowest
results. The simplified Level 2.5 scheme, implemented using the numerical methods of Annan wAnnan, J.D., 1999.
Numerical methods for the solution of the turbulence energy equations in the shelf seas. Int. J. Numer. Methods Fluids 29,
193–206x, produces results, which give the best agreement with the available data.
