² Continuous samples were obtained through frequent downloading of the instrument buffers, but the system was not designed for continuous recording (individual data points are not time-tagged). Several overlapping pressure time series were visually "spliced" to generate the multi-hour time series illustrated. Thus, some uncertainty exists about the exact times and completeness of the data points, and the synchronization between the offshore and inside time series has not been substantiated. However, this will not materially affect the present discussion for either signal considered separately.