AMLR 2004 Weekly Report No. 8

29 February 2004

1. Our current position is station D03-02, in the Elephant Island area of the AMLR large area survey grid, where we are conducting the second of two surveys of bio-oceanographic conditions in the vicinity of the South Shetland Islands. Our progress has been steady with little influence to our cruise track by weather or ice. Minor equipment troubles were put right in short order causing only minor delays in sampling efforts.

2. Krill biomass and dispersion. Mean krill biomass density in the West Area was 11.1 gm^-2, less than last legs estimate of 29 gm^-2. Krill were distributed in the highest concentrations west of Livingston Island along the shelf break. In the Elephant Island area, highest densities of krill were mapped around the Shackleton fracture zone and north of Elephant Island. Myctophids were mapped in the area of Elephant Island, north of the shelf break.

3. Instrumented buoys. The two instrument spar buoys moored off of Cape Shirreff in the vicinity of a submarine canyon were reported to be communicating erratically with data logging computers placed at Cape Shirreff during Leg I; it was decided to delay recovery of the buoys until to the end of the survey.

4. Zooplankton and krill. Results from over 70% of the Elephant Island area samples indicate a major ecological change between the 2004 Surveys A and D. Copepod abundance has increased by over an order of magnitude, the change in large part due to elevated numbers of oceanic species, Calanus propinquus, Calanoides acutus and Rhincalanus gigas, relative to coastal species, Metridia gerlachei. Abundance of Thysanoessa macrura and Euphausia superba larvae, which have generally offshore distributions, also increased by several orders of magnitude compared to last month. Abundance of post larval krill and Thysanoessa macrura in the Elephant Island area were similar to the January values. Salpa thompsoni was ca. 1/3 less abundant than the previous month. These results parallel those based on the West Area samples. Both krill and salps have had prolonged reproductive activity over the 2003/2004 season. Reproductively mature krill dominated the Elephant Island catch with 80% of the females either gravid or spent. Larval stages ranged from early calyptopis 1 to relatively advanced furcilia 3. These results indicate a late November to late February spawning period. Large reproductive solitary stages comprised 20% of the salp catch while about half of the aggregates were small recently released forms. These results indicate an unusually late-season pulse of chain production.

5. Oceanography and meteorology. Weather conditions during the week were moderate with winds mainly west to north- west at an average speed of approx.15 knots, gusting to 35 knots for short periods on Tuesday and Saturday. Pressure readings increased at the beginning of the week to peak at 1016 mb and dropping steadily to a low of 987 mbar at the end of the week. Weather conditions were mostly overcast during the week, with air temperatures ranging between 1ºC and 4ºC. 47 CTD stations were occupied, including the last few stations of the West Area and the major part of the Elephant Island Area. On Tuesday evening the CTD underwater unit malfunctioned and had to be replaced with the spare unit. The faulty unit was opened to ensure that flooding had not occurred. According to the Water Zone Classification table, Zone 1 (ACW) type waters were clearly defined at the offshore stations of the West Area and to the north west of Elephant Island. The stations south of Elephant Island were predominantly mixed (Zones 2 and 3), with evidence of Zone 4 water on the southern shelf, between King George and Elephant Islands.

6. Phytoplankton. As noted in the last report water column integrated (0 m to 200 m) Chlorophyll values are about half the magnitude as seen on Leg 1 of the 2004 AMLR Survey or the West Area (centered 18-08) and Western Elephant Island Area (centered 08-04). Typical integrated Chlorophyll values for the West Area and Western Elephant Island areas are 17 mg m^-2 and 22 mg m^-2 for Leg 1 and 10 mg m^-2 and 15 mg m^-2 for Leg 2 respectively. Surface Chlorophyll values are more similar across both legs at less than 0.5 mg m^-3 for both areas. These values do not include the “Blue Water Zone” (centered about 09-03) that is currently being studied by the R/V Gould (a NSF-sponsored program). Chris D. Hewes transferred to the R/V Gould at the end of Leg 1 and we are coordinating sampling in this area. We have adjusted sampling of the CTD Niskin bottles in this region to study deep (c.a. 110 m) Fluorescence maximum.

7. Predator Diet Studies. 76 Antarctic fur seal scats have been analyzed. The week 8 scats contain mostly a mix of krill and fish with one sample containing krill, fish and squid. 79 Antarctic fur seal milk samples have had the lipid extracted. These samples will be completed and analyzed in the lab in La Jolla. 27 fish (a mix of G. nicholsi, G. braueri, E. carlsbergi and E. antarctica) and 7 groups of krill have been ground and will be analyzed for their fatty acid content in La Jolla.

Submitted by Adam Jenkins