Situation Report, Cruise NBP96-4A;    October 22, 1996, 0800 GMT

The AESOPS Process Study I began science operations in earnest this week, and at this time have completed 26 CTD (hydrographic and trace metal clean) casts, eight MOCNESS tows, eight trace metal casts, two in situ deployments, eight in situ pumping casts, and six ring net tows. We began our work at Site Orca (76 deg. 30 min. S, 178 deg. W) with a long (ca. 30 h) station with multiple operations, and have transited across the southern Ross Sea towards the coast. We occupied stations every two degrees along 76 deg. 30 min. S and completed multiple operations at each station. The transect will end tomorrow at Site Minke (76 deg. 30 min. S, 168 deg. E), where another long station will be conducted. The weather has been variable at our stations, with temperatures ranging between -12 and -25 deg. C, and winds between 6 and 50 knots. Wind chill factors have reached -77, conditions which can be hazardous to the health of workers. These circumstances have also created difficult operational conditions. For example, we have had difficulties with all water casts, in that either the bottles and spigots themselves or the winches used to raise and lower the bottles have frozen to some degree. Water temperatures are at the freezing point of seawater, and hence any heat loss initiates frazil ice formation. Samples incubated for rate processes have begun freezing immediately upon removal from incubators. Despite these conditions, we have begun to characterize the carbon dynamics of the region. Ice cover remains substantial, although in some areas the ice is only ca. 0.4 m thick. Noon-time irradiances are high (>1,000 uE/m2/sec), but surface layer light levels are only 30% of those values. The water column is unstratified, and at at least one station the mixed layer extended from the surface to the bottom. Nutrient concentrations are high and do not reflect any biological removal. Chlorophyll levels were low (ca. 0.1 ug/l), and rates of production were correspondingly low. The phytoplankton appear to be dominated by flagellated forms of Phaeocystis. Zooplankton and bacterial biomass also was low. These conditions apparently represent those commonly found at the start of the annual phytoplankton bloom in the Ross Sea. After the completion of station work at Site Minke, we will return to Site Orca for our second occupation of that location, and then will transit south towards the Ross Ice Shelf, where we expect to encounter waters with reduced ice cover and increased biological activity. We will also assess these waters for trace metal and thorium concentrations. Occupation of these waters will provide a comparison with the late winter conditions found along 76 deg. 30 min. S and a chance to sample an early spring, ice-free environment. The science party looks forward to this opportunity. Submitted: Walker Smith, Chief Scientist