Abstract
A long-term temperature monitoring experiment for about one year was carried out at a biological community east of the Hatsushima Island, western Sagami Bay.Three temperature probes, which are 60 cm to 90 cm in length, had been penetrated into the sediment within 20 m of the colony, and one sensor was installed for monitoring the bottom water temperature. Temperatures were measured once a day. The obtained temperature records showed fluctuation that is clearly attributed to variation of the bottom water temperature. The fluctuation was successfully eliminated by subtracting a theoretical temperature variation derived from the Fourier transform of the water temperature data. During this procedure, two unknown parameters, geothermal gradient and thermal diffusivity, could be precisely determined, using the non-linear least squares method. Thus, long-term monitoring of the water and subbottom temperature is very useful for determination of geothermal gradient and heat flow, in cases where the effect of the bottom water temperature variation is significant.
