Short‐term variability in the bottom boundary layer of the deep Ocean

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Abstract
A series of 130 CTD profiles of temperature and salinity were measured in and above the benthic homogeneous layer at a location on the Blake‐Bahama Outer Rise (28°00′N, 71°30′W). Four sets of measurements were made over a 3‐day period. In order to observe the short‐term behavior of the boundary layer, individual profiles in each set were separated in time by about 4 min or in distance by about 30 m. Layer thickness changes of up to 20 m were observed in less than an hour. The fact that the variations in homogeneous layer thickness and the shape of the overlying temperature gradient are coherent and progressive suggests internal waves as a source of short‐term thickness variability. At the site where the greatest short‐term variability was observed, this interpretation is supported by the calculated Brunt‐Väisälä period (2.3 hours) and the lack of correlation between the thickness and temperature of the homogeneous layer. At another site, however, increasing layer thickness was accompanied by rising temperature within the layer, a feature indicating that mixing in of the overlying water may also produce thickness changes.

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