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Wed, 26 Apr 1995 12:58:45 +0000 (GMT)

Cruise Update from Chief Scientist, Robert Weller

Mooring Recovery and Redeployment Cruise

TTN-046 left Muscat April 14 and steamed directly to the moored array, dropping hourly XBTs (T7, 760 meter deep profiles). Dan Rudnick's two surface moorings, SIO North (SIO N) and SIO South (SIO S), Charlie Eriksen's southern PCM mooring (UW S), and Bob Weller's central surface mooring (WHOI) were recovered and redeployed. One 4,000 m CTD, several 1,000 m CTDs, and a number of 200 m CTDs were done before recovery and after deployment to obtain data to calibrate moored temperature and salinity sensors and determine the local buoyancy and sound speed profiles. The ship's IMET sensors and additional WHOI sensors installed on the ship were used to provide information about the calibration of the moored meteorological sensors. On three days, a drifter with temperature sensors concentrated in the upper 3 m was deployed in the vicinity of the WHOI mooring from sunrise to sunset to observe diurnal heating. The CTD was yo-yo'd from the surface to 50 m during the drifter deployments. Several patterns were steamed in and near the array to examine the spatial scales of the upper ocean currents using the shipboard ADCP. Instruments deployed by John Marra (LDEO), Tom Dickey (USC), and Van Holliday (Tracor) were recovered and redeployed on the WHOI mooring in addition to the WHOI instrumentation. Work is underway on board to read the data stored in the instruments recovered from the moorings. Early indications are that the data return rate was good. High currents prevailed for approximately the first 60 days after the deployment of the moorings last October with speeds as high as 130 cm/s. Temperature and salinity records show a cooling, freshening surface mixed layer starting in December that reaches 110 m depth by February, then warms and shoals beginning in March. Given the very light winds observed over the winter Northwest Monsoon, it will be interesting to identify the processes responsible for the observed mixed layer evolution. Heavy biofouling (primarily gooseneck barnacles) was found on the WHOI buoy hull and the 5 and 10 m deep instruments on WHOI mooring. The impact of the biofouling on the data is not yet fully understood, but the LDEO and USC MVMS indicate that biofouling was minimal during the first 90 days. Some low oxygen corrosion was noted on stainless steel components located between 100 and 150 m. Both the biofouling and low-oxygen corrosion were very localized, with instruments 10 m away unaffected. Clear, blue water with numerous sharks, some tuna and some mahi was found around the moorings. Winds and cloud cover were light to vanishing with. Clear sky with air temperatures about 28.5 deg C and sea surface temperatures about 29.5 deg C. When not steaming, temperatures on deck were considerably higher. An on-deck temperature (at the aft, starboard crane, about 4 feet off the deck) of 43 deg C was observed on the afternoon of the last mooring deployment. At this point, the first six months of the mooring program is judged a success. The shipboard technicians and crew of the Thompson have provided excellent support. TTN-046 will leave the array late on the 26th to make an hourly XBT line along the track taken during the SeaSoar cruises. Arrival in Muscat is scheduled for the morning of April 29. Robert A. Weller is