AMLR 2004 Weekly Report No. 7

 

22 February 2004

 

1. Our current position is station D16-08 in the west area of the AMLR large area survey grid. The ship is underway conducting the second of two surveys of bio-oceanographic conditions in the vicinity of the South Shetland Islands. The survey is divided into four areas: the South Area in the central portion of Bransfield Strait south of King George and Livingston Islands, the West Area north of King George and Livingston Islands; the Elephant Island Area encompassing the northern portion of the South Shetland archipelago; and the Joinville Island Area in the western portion of Bransfield Strait. This survey is expected to take 16 days to complete if weather and ice conditions are manageable.

 

2. During a three day import in Punta Arenas, Chile personnel were exchanged, provisions and fuel were supplied to the ship. The ship then departed on time at 0900 on the 17th.

 

3. First item of business was a call on Cape Shirreff field camp. The crossing of the Drake was uneventful and we fetched Cape Shirreff 12 hours ahead of schedule. Upon arrival mid-day on the 19th of February, personnel (R. Holt) along with provisions, propane fuel and mail were transferred to the shore camp via zodiac. Directly after finishing the resupply of Cape Shirreff the ship began the second survey.

 

4. Krill biomass and dispersion. Mean krill biomass densities along the first 5 transects in the West Area ranged from 3 to 28 g m-2, less than densities observed in this area last leg. Krill were mapped along all transects with highest densities (over 2 kg m-2) near the shelf break north of Livingston Island.

 

5. Instrumented buoys. Communications between the instrument spar buoys and the Cape Shirref base station were intermittent. Buoy 3 is currently reporting low battery voltages, most likely as a result of the foggy and overcast conditions, which impede charging of the system batteries. Buoy 1, although still communicating with the base station appears to be more erratic, possibly as a result of drift in the crystal timebase.

 

6. Zooplankton and krill. Although present in 10 of 16 West area samples krill have not been abundant. The 220 individuals so far collected provide mean and median abundance values ca. half those from the same area during Survey A. Salpa thompsoni abundance in this area also has decreased with values ca. 1/3 those of the previous month. As before, low numbers of Ihlea racovitzai over South Shetland Island shelf indicates an intrusion of Polar Slope water from the east. In contrast, copepod abundance has increased by an order of magnitude. This increase is in part due to seasonal ontogenetic migrations to the upper water column. However, substantial numbers of Rhincalanus gigas, a subantarctic species, and increased copepod diversity at offshore stations indicate an oceanic influence that was essentially absent during Survey A. This is supported by observations of Type 1 (Drake Passage) water at offshore Survey D stations (see Physical Oceanography report).

 

7. Oceanography and meteorology. A weakly-defined Antarctic Polar Front was crossed between Latitude 58 48S and Latitude 59 50S, with the sea surface temperature dropping from 6.67C to 4.16C and a corresponding decrease in salinity from 34.04 ppt to 33.71 ppt. Weather conditions during the week were mostly calm with winds from the north-west at an average speed of approx.12 knots, gusting to 30 knots for a short period on Friday. Pressure readings decreased from a high of 1016 mbar at the start of the transit to 995 mbar, remaining constant at this level for the rest of the week. Air temperature ranged between 2C and 3C in foggy and overcast conditions during the week. 16 CTD stations were occupied in the western part of the West Area. According to the Water Zone Classification table, zone 1 (ACW) type waters were more clearly defined at the offshore stations, than during leg1. Inshore stations were predominantly type 2 water.

 

8. Phytoplankton. In addition to the standard in-situ Fluorometric Chlorophyll and associated Phaeopigments we are once again sampling water taken from the CTD Rosettes for POC, HPLC Pigments, MAA Pigments, near UV and visible absorption spectra and (new to this leg) POP (Particulate Organic Phosphorous) and nutrients. We are also deploying our suite of optical instruments to measure the underwater light field and the inherent optical properties of the seawater and its constituents. Early results indicate a different productivity in the West Area. The integrated Chlorophyll (0 m to 200 m) is about half of what it was in this area on Leg 2. This is most likely a response to diminished Photosynthetically Available Radiation (PAR: the available light in the water column for the phytoplankon) since we have been under heavy fog since the survey began. Of note though is the surface values of Chlorophyll are similar to the last survey for the region.

 

9. Underway seabird and marine mammal observations. A visual seabird survey using a standard 300 M strip transect was conducted during the daylight hours while the ship was transiting across the Drake Pasage to the AMLR study area. In addition, all marine mammal sightings were recorded on an opportunistic basis. Beginning at the south end of Estrecho de Le Maire, twelve and a half hours of visual survey effort covered 193 nm of track line, ending about 60 nm north of Livingston Island. Observation effort was curtailed early on the third day because of limited visibility in snow. Otherwise, observation conditions were excellent with an average sea state of Beaufort 3 and no glare. Avian abundance was extremely low, a total of 149 individuals, although diversity was about average with 16 species. Noteworthy was the low number of prions, Blue Petrels, all albatross, Sooty Shearwater and giant petrels. Eleven Soft-plumaged Petrels were seen, about average for this often scare and erratic late summer visitor. There were 8 marine mammal sightings representing 4 species. Outstanding was a close range encounter with a small group of Cuviers Beaked Whales, an unexpected first for AMLR cruises; another sighting of 2 unidentified beaked whales was likely this species. Other cetaceans were Hourglass Dolphin, Fin and Humpback Whales.

 

10. Predator Diet Studies: To date 62 Antarctic fur seal scats have been analyzed. The week 7 scats contain a mix of krill, fish and squid. Week 8 and 9 scats were picked up from the Cape Shirreff field camp on Thursday, February 19, 2004. To date 51 Antarctic fur seal milk samples have had the lipid extracted. These samples will be completed and analyzed in the lab in La Jolla. No additional krill or fish samples have been available for analysis during Leg II.

 

 

11. Scientific party aboard includes:

A. Jenkins, SWFSC, Chief Scientist, small boats,

A. Cossio, SWFSC, acoustics

V. Loeb, Moss Landing Marine Labs, zooplankton

R. Rowley, MLML, small boats, zooplankton

N. Gong, UCSC, zooplankton

M. Force, SWFSC, zooplankton, bird and marine mammal observations

K. Chambers, SWFSC, zooplankton

S. Sessions, SWFSC, zooplankton

E. Daniels, MLML, zooplankton

M. Soule, FRS, Cape Town, oceanography, ET support

M. Van Den Berg, STS, Cape Town, oceanography, ET support

D. Allison, SIO, phytoplankton

J. Ryan, SIO, phytoplankton

T. Reddy, Stanford U, Phytoplankton

L. Smith, Auburn Drive HS, lipid extractions and scat analysis

 

 

Submitted by Adam Jenkins