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MISSION DISPATCH 7 • 4/21/01 - 4/22/01 Today's Weather - images courtesy of NOAA & RSMAS Weather Puts Sub Dives on Hold The R/V SEWARD JOHNSON casts off from Fort Pierce at 1307 on Saturday, to head back to the western Gulf Stream 
and attempt to make scheduled dives aboard the JOHNSON SEA-LINK research
submersible.
Unfortunately, the weather does not cooperate. By the scheduled 1930 dive time, winds of 20 knots with higher gusts were blowing out of the east, and seas were running 5-7 feet. These conditions translate into a "Force 5" Sea State on the Beaufort Scale. Under moderate Force 5 conditions, the sub crew might proceed with a dive during daylight hours. But everything becomes just a little trickier at night, so submersible operations have been suspended pending an improvement in weather conditions. That improvement does not come. Throughout the evening of the 4/21-4/22, and during the following day, a Force 5 Sea State persisted, necessitating the continued suspension of sub ops. Two More Days of MOCNESS Sets Conducted Shortly after arriving back on site in the western Gulf Stream on Saturday, the Science Team conducted another set of MOCNESS tows. The set began at 1600 at navigational coordinates 27°29.9'N and 74°49.4'W. The target tow speed was reduced to 1.5 knots, although sea conditions resulted in actual tow speeds that were somewhat higher. Each of the eight tow segments integrated 200-300 cubic meters of water and approximately 20 meters of vertical water column, between 70 and 90 meters depth. The set was conducted in "tow-yo" fashion, as described in the previous day's dispatch. The target depths were set by the fact that the thermocline, pycnocline, and chlorophyll maximum zone all occurred within that range at the time of the tow. These zones are generally areas of the mesopelagic (midwater) ecosystem with high particle and organism abundance. The MOCNESS array was recovered at the end of Saturday's tow at 1715. 
Despite the fact that the decreased tow speed did leave delicate gelatinous animals in
somewhat better condition than in previous sets, there were still no appendicularians
detected in the collections.
Three more MOCNESS tow sets were conducted on Sunday, 4/22, at 1039,1418, and 1945. The morning set was deployed at navigational coordinates 27°45.16'N and 79°44.99'W, the afternoon set was put out at 27°45.16'N and 79°44.99'W, and the evening set at 28°01.49'N and 79°41.78'W. Lots of great faunal diversity, including large numbers of predatory chaetognaths or arrow worms. Appendicularians remained "invisible" to the nets, however. We will head back to the dock at Fort Pierce to drop off Science Team member Alexander Bochdasky. Then we will return to the Gulf stream dive sites and wait for the seas to calm down so that sub ops can be resumed. This expedition is made possible through a grant from the Biological Oceanography Program of the National Science Foundation with additional support from Harbor Branch Oceanographic Institution.  | |
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