AMLR 2004 Weekly Report No. 9

7 March 2004

1. Our current position is 8 nm NE of Cape Shirreff, the ship is in transit to Admiralty Bay. Yesterday afternoon we finished the second of two surveys of bio-oceanographic conditions in the vicinity of the South Shetland Islands. After finishing the survey, the ship transited to Cape Shirreff and anchored offshore. This morning we recovered AMLR personnel and equipment without incident effectively closing Cape Shirreff Field camp for the winter. In addition the two instrumented buoys deployed during Leg I were recovered to the ship. The ship should fetch Admiralty Bay in the early morning hours of the 8^th; we will then calibrate the ships scientific echosounder and close Copacabana Camp for the winter.

2. Krill biomass and dispersion. Mean krill biomass for all of survey D is 24.13 g/m², 1 g/m² less than survey A. The highest amount of krill biomass was found around Elephant Island. The south area had twice the mean biomass than survey A. Overall biomass is up from 20.10 g/m² for the 2003 survey to a mean of 24.63 g/m².

3. Instrumented buoys. Both instrumented spar buoys and ground tackle were successfully recovered to the ship without incident. Inspection of buoys showed no apparent structural damage after spending 5 weeks moored at their respective waypoints.

4. Zooplankton and krill. Krill had a very patchy distribution within the South area. While catches were generally small, two of the 17 samples here had extremely large krill concentrations; one of these yielded an estimated 6400 krill, the largest catch of the entire 2004 survey effort. These samples were dominated by immature stages with lengths centered around a 35 mm mode. Salpa thompsoni abundance, similar to that in the Joinville Island, was an order of magnitude smaller than in the West and Elephant Island areas. Ihlea racovitzai was present at the majority of stations but its distribution indicated a diminishing influence of Polar Slope water in the northwest portion of Bransfield Strait. Copepod abundance was the lowest of all four area surveyed due to relatively low concentrations of all species including coastal species, Metridia gerlachei.

5. Oceanography and meteorology. Winds blew mainly west to northwest until Tuesday, switching to easterly for the remainder of the week. Average wind speed was 20 knots with an increase to over 40 knots on Thursday when the pressure dropped to a low of 968 mbar. 28 CTD stations were occupied, including the last few stations of the Elephant Island area, the northern part of the Joinville area and the South Area. According to the Water Zone Classification table, predominantly mixed (Zone 2 and 3) waters were found in the eastern part of the Elephant Island Area. In the northern sector of the Joinville Area mainly Zone 4 waters were found, with the 3 most southern stations being Zone 5 waters. The waters of the Bransfield Strait (South Area) were predominantly Zone 4, with Zones 2 and 3 found at the inshore stations.

6. Phytoplankton. As noted in earlier reports the surface and water column integrated (0 m to 200 m) Chlorophyll values for the West Area and the Western Elephant Island Area were only about one half the magnitudes as seen on Leg 1 of the 2004 AMLR Survey. As we completed the Elephant Island Area we finally encountered higher productivity centered on stations D05-08 and D04-07. The maximum surface Chlorophyll values thus far were measured at 2.51 mg m^-3 and 2.36 mg m^-3, respectively. Water column integrated Chlorophyll values for the transect D05-08, D04-07, D02-06 were calculated at 35.98 mg m^-2, 32.36 mg m^-2, and 25.07 mg m^-2, respectively. With this increase of autotrophic biomass we observed a marked increase in zooplankton in our water samples. Ice halted our survey of the Joinville Area at D04-10. Early results of Chlorophyll and productivity data for the beginning of the South Area indicate that this region of higher productivity will continue into the Bransfield Straight.

7. Predator Diet Studies. 90 Antarctic fur seal scats were analyzed on the ship. The week 9 scats contain mostly a mix of krill, fish and squid. Three samples contained no sign of krill. One scat had seven squid beaks. Antarctic fur seal milk samples have had the lipid extracted. These samples will be completed and analyzed in the lab in La Jolla. 44 fish (a mix of G. nicholsi, G. braueri, E. carlsbergi and E. antarctica) and 16 groups of krill have been ground and will be analyzed for their fatty acid content in La Jolla.

Submitted by Adam Jenkins