Seasonal variations of the sediment compressional wave-speed profile in the Gulf of Mexico

Abstract

The seasonal variation of the sediment compressional wave-speed profile due to temperature variability in the water column is investigated for shallow-water regions, where large temperature fluctuations can occur during the course of a year. For example, in water depths of less than 30 m in the Gulf of Mexico, field observations indicate that the annual fluctuation of the ocean bottom temperature is approximately sinusoidal with a peak-to-trough value of about 15 °C. The heat flow across the water/sediment interface results in the variation of the pore water temperature with season. It is shown that the compressional wave speed varies approximately linearly with pore water temperature, an effect which is, to first order, independent of both the porosity and given sediment type. Further, the velocity ratio (ratio of sound speeds in the water and the sediment at the water/sediment interface) is shown to be independent of temperature but dependent on sediment type. The effect of variations in water column temperature on sediment compressional wave speed is demonstrated by inversions of two data sets. The data were obtained at the same location in the Gulf of Mexico but at different seasons. Finally, the importance of these variations is studied by considering their effect on (a) the prediction of the pressure field in the water column and (b) the errors introduced in source localization by matched-field processing.