科研之友
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摘要
Accurate representation of light attenuation by inorganic suspended particulate matter (SPM) is one of the major factors limiting realism in coupled physical-biogeochemical models used to simulate primary production in shelf seas. The main problem is the accurate calculation of SPM concentrations. A multiple-grain size advection-diffusion method is presented, and results are compared to observations. The method has been incorporated in the 1-D hydrodynamics model General Ocean Turbulence Model. Particular attention has been given to the representation of sediment pickup, which is based on upward diffusion of sediment from a reference concentration near the seabed. Also, a bulk approach is used where the dominant fraction governs the pickup of the other fractions. A seabed model using the active layer approach is included. Moreover, to better represent seasonal cycles in background SPM concentration, a temperature-dependent kinematic viscosity is used, which modifies settling velocities and sediment pickup. Model results were tested against multiyear time series of surface observations of SPM using an Optical Backscatter sensor on "SmartBuoy'' at two sites on the UK shelf and against suspended load observations obtained from Niskin bottle samples. It was found that at least four size fractions are required for reasonable predictions of the SPM concentration at the two sites: a coarse fraction representing the median grain size of the seabed sediments, two silt fractions responsible for most of the variability near the sea surface, and a clay fraction that provides a background concentration with slow variations in time. The method can easily be extended to 3-D models.
- 出版日期2009-3-12
