STABILITY OF THE ANNUAL TEMPERATURE CYCLE IN SHELF SEAS

1. In shallow well-mixed seas the sea temperature follows closely that of the ambient air temperature with limited separate effect of solar heating. Conversely in deep water, the annual variation in sea surface temperature variations will be less than that of the ambient air. In such deep water the annual variation will decrease with increasing depth and maximum temperatures will occur up to 3 months after the maximum of solar heating. Generally, inter-annual variability of sea surface temperatures will be less than corresponding variability in either the effective solar heating, QI, (reduced by cloud cover) or the surface loss coefficient, k, (increased by stronger winds). The annual-mean sea temperature will exceed the annual mean air temperature by the annual mean of QI divided by k. 2. The time taken for solar heating to be equalised throughout the water depth, D, is given by T-V=D-2/K-2 (K-2 a vertical eddy dispersion coefficient). T-V ranges from a day or less when D approximate to 10 m to in excess of 1 year when D > 500 m. 3. The effects of stratification on the annual cycle generally become increasingly apparent for values of T-V > 20 days. Overall, stratification insulates the sea, (especially at greater depths) from atmospheric influences. In combination with autumnal overturning, the effect is to lower both the variability and mean of the temperature in deeper water. 4. The relative influence of variability in adjacent oceanic conditions depends on the ratio D:F-T where F-T is the flushing time of the shelf sea relating to oceanic exchanges.