Investigation of the Bottom Boundary Layer during the Georges Bank
GLOBEC Stratification Study
INVESTIGATORS:
J. Churchill
Woods Hole Oceanographic Institution
Woods Hole, MA
email: jchurchill@whoi.edu
A. Williams
Woods Hole Oceanographic Institution
Woods Hole, MA
email: awilliams@whoi.edu
GRANT PERIOD: October 1993 - June 1995
STATEMENT OF OBJECTIVES:
To examine turbulent mixing and its influence on stratification
in the bottom boundary layer over the southern flank of Georges
Bank.
STATEMENT OF WORK:
Our study of stratification and mixing in the bottom boundary layer on
Georges Bank began with the deployment of a BASS (Benthic Acoustic Stress
Sensor) tripod at station ST1 (40 51'N, 67 33'W) on 3 February 1995. The
BASS was equipped with 5 acoustic current meters located from 0.25 to 4.5
m above bottom. These sampled the flow at 2 Hz for 7.5 min. every half
hour. Also attached to the BASS were: 8 thermistors, 5 optical
backscatterance sensors (to estimate suspended particulate concentration),
a pressure sensor, a CTD and Benthos camera and strobe. The BASS was
scheduled for an at-sea turn-around with data recovery in mid-April.
Unfortunately this was not successful. Only one of the two buoyed
recovery lines on the BASS released upon command. Before it could be
retrieved, it wrapped around the mooring chain of the SW guard buoy at ST1
and severed on the mooring chain when recovery was attempted. On June 7 a
second recovery attempt using the SeaProbe Submarine also failed. A third
recovery attempt with the SeaProbe was successful and the tripod was
returned to WHOI on 11 July. The tripod sensor data, which extended till
mid-June, have been recovered and are now being processed.
To acquired further bottom boundary layer measurements during a time of
"mature" stratification, a second BASS tripod was deployed at ST1 on July
12. This was outfitted with the same complement of current meters and
thermistors as were attached to the first BASS tripod. It is slated for
recovery on 19 August.
Analysis of the tripod measurements, coupled with modelling of bottom
mixing, will be carried out over the next year.