The influence of different turbulence schemes on modelling primary production in a 1D coupled physical-biological model

A one-dimensional(1D) coupled physical-microbiological model has been appli ed to a site in the central North Sea. The impact of the choice of the turb ulence closure scheme on the modelling the primary production has been inve stigated. The model was run with four different parameterisations of vertical mixing of heat, momentum and dissolved and suspended matters, using M2 tidal forci ng and the hourly mean meteorological forcing of 1989 to reproduce the annu al thermal structure and primary production. The four mixing parameterisati ons are. Level 2 turbulence closure scheme [Mellor, 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. Sp ace Phys. 20 (4) 851-875] using an explicit numerical scheme [Sharples, J., Tett, P., 1994. Modelling the effect of physical variability on the midwat er chlorophyll maximum. J. Mar. Res. 52, 219-238]; a version of the Level 2 .5 turbulence closure scheme [Galperin, B., Kantha, L.H., Hassid, S., Rosat i, A., 1988. A quasi-equilibrium turbulent energy model for geophysical flo ws. J. Atmos. Sci. 45, 55-62; Ruddick, K.G., Deleersnijder, E., Luyten, P.J ., Ozer, J., 1995. Haline stratification in the rhine/meuse freshwater plum e: a 3D model sensitivity analysis. Cent. Shelf Res. 15 (13) 1597-1630] sim plified to use an algebraic mixing length by Sharples and Simpson [Sharples , J., Simpson, J.H., 1995. Semidiurnal and longer period stability cycles i n the Liverpool Bay region of freshwater influence. Cent. Shelf Res. 15, 29 5-313], also solved explicitly; the same simplified L2.5 scheme with an imp licit numerical solution and modified vertical discretisation scheme [Annan , J.D., 1999. Numerical methods for the solution of the turbulence energy e quations in the shelf seas. Int. J. Numer. Methods Fluids 29, 193-206]; and another version of the same scheme (but using a different algebraic mixing length) as described by Xing and Davies [Xing, J., Davies, A.M., 1996a. Ap plication of turbulence energy models to the computation of tidal currents and mixing intensities in the shelf edge regions. J. Phys. Oceanogr. 26, 41 7-447; 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 th e internal tide. Int. J. Numer. Methods Fluids 26, 1055-1084]. Various mode l outputs at the sea surface and in depth profiles have been compared with data collected in 1989 as part of the North Sea Project [Huthnance, J.M., 1 990. Progress on North Sea Project. NERC News, vol. 12, pp. 25-29, UK]. It is shown that the biological results are extremely sensitive to the small c hanges in the physical conditions, which arise due to the different turbule nce schemes tested. The timing of the spring bloom and the maintenance of t he 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 nume rical methods of Annan [Annan, J.D., 1999. Numerical methods for the soluti on of the turbulence energy equations in the shelf seas. Int. J. Numer. Met hods Fluids 29, 193-206], produces results, which give the best agreement w ith the available data. (C) 2000 Elsevier Science B.V. All rights reserved.