Bottom Currents During Early Winter on South Texas Continental Shelf: Implications for Shelf Sediment Transport: ABSTRACT

Abstract

During a 42-day period in the early winter of 1981, bottom currents and temperature were measured by a current meter moored 2 m off bottom in 130 m of water on the south Texas continental shelf. During this time, nine cold fronts passed over the area, bringing about substantial changes in the overlying wind field. Particularly significant were the strong southeasterly winds that preceded several of the frontal passages. These wind events appear to have indirectly affected the bottom current velocity structure. During the early part of the record, bottom currents averaged 10 cm/sec, with bursts up to 32 cm/sec. Flow was generally along the shelf to the southwest until late in the time series when net water motion changed abruptly to become southeasterly (toward deeper water). Current speeds then averaged 13 cm/sec with peaks of up to 26 cm/sec. The cause of this unusual offshore bottom water motion is believed to be best understood by study of the bottom water temperature record. It is hypothesized that during the latter part of the record , when southeasterly winds were strongest, surface water was driven toward the coast. However, bottom water was advected in the opposite direction, resulting in coriolis-deflected offshore flow. A noticeable rise in the bottom water temperature accompanying this motion suggests advection of warmer coastal waters into deep water. Hydrographic surveys show a slight deepening of the thermocline at this time. This time series is significant for several reasons. First, data on the current velocity field of the south Texas continental shelf is sparse. Second, the current speeds measured are for some periods in excess of that which, theoretically, is necessary for the transport of fine (3 ^phgr) sand. Third, the record shows an apparent interaction between bottom currents and the overlying wind field. End_of_Article - Last_Page 308------------