The influence of optical water type on the diurnal response of the upper ocean

The effect of optical water characteristics upon the diurnal variability of upper ocean temperatures and heat content has been studied. A second moment turbulent closure scheme was employed for the simulations. Realistic thermal forcing as well as uniform and time varying wind stresses were used for boundary conditions. The diurnal amplitude in sea surface temperature and long term changes in heat content are strongly influenced by water type for constant wind speeds up to 6 m s^-1. The phasing of time-dependent wind stresses can lead to enhanced diurnal sea surface temperature amplitudes (e.g. solar insolation 12 hours out of phase with maximum wind stress). Long term trends in heat content, however, are nearly independent of phase. The results of the simulations are consistent with the range of reported observations. The present work suggests that variability in biological productivity and consequent variations in the optical properties of seawater may be important for realistic modelling of upper ocean structure and climate.