Date: Wed, 17 Dec 1997 08:00:59 -0500
2nd Weekly Progress Report December 17, 1997 REVELLE Process 1 cruise has completed 6 stations and is now on Sta. 7 at about 64'09"S and 169'30"W. This station is within a few miles of the pack ice edge. It has been foggy, so we haven't seen the solid ice; but Capt. Arsenault said that when the fog lifted for a few minutes those on the bridge could see a white line a few miles off. We passed about a dozen big icebergs and lots of small chunks of ice as we approached the ice edge. SST at Sta. 7 is -1.0C but down 40m it is -1.74C. There is a particle and fluorescence maximum at the top of the subducting cold water. Current is strong, about 1.1 knots, but varying in direction. The bottom of a layer of -1.7C water is around 190 m; a few meters deeper the temp increases to +1.7C. There is lots of structure in the upper 200 m in all the properties, very unlike the deep mixed layer Survey 1 observed south of the front. All the Process 1 programs are progressing very well. The seas have remained moderate, never more than 12 ft., usually 8 ft. and occasionally 6 ft. We have lost no time to weather so far. Yesterday the barometer fell from 1013 to 986 mb in 8 hr, but the seas didn't exceed 12 ft. The sea ice seems to dampen the swell. The trace metal group, Measures and Elliot, reported steadily decreasing surface Fe concentration as the ship worked south. The values at the ice edge are from 0.12 to 0.14 nM Fe. Biomass of phytoplankton and zooplankton has varied widely with euphotic zone chlorophyll concentrations from 0.15 to 2.15 mg m-3. Productivity has varied from a modest 600 mgC m-2 d-1 to a high of 3220. It's hard to believe there is light, nutrient or micronutrient limitation on the basis of the high values. We have several excellent microscopes aboard. The micrograzing group (Selph, Albert and Allen) can display the material on their microscope slides on a video screen for all to view simultaneously. The water at the high biomass location is loaded with big diatoms. Nutrients are, of course, extremely high. At this ice edge station the nutrient folks (Krogslund, Guffy and Codispoti) find about 45 uM Si and 20 uM nitrate. The particle-optical profiling system (POPS) is getting a thorough workout by Walsh, Searson and Gunderson. The complex particle layering in the subducting layers will give them material to work on for a long time to come. If the fog lifts we plan to reconnoiter along the ice edge, but if not, we'll turn north and fill in stations around Mooring #4. For now it looks as though 64'09"S may be as far south as REVELLE Process 1 is going. All is going very well; we will probably make at least 10 long stations along the section. Regards, Dick Barber, Chief Scientist 17 December 1997