20 January
2002
1. Current position is approximately 50 miles west of Elephant Island conducting a survey of bio-oceanographic conditions in the vicinity of the South Shetland Islands. The survey is divided into four areas: the West Area north of King George and Livingston Islands; the Elephant Island Area encompassing the northern portion of the South Shetland archipelago; the Joinville Island Area in the western portion of Bransfield Strait; and the South Area in the central portion of Bransfield Strait south of King George Island. Survey operations in the West Area were completed this past week. Earlier in the week personnel and provisions were transferred ashore at the Copacabana (Admiralty Bay, King George Island) and Cape Shirreff (northern shore of Livingston Island) field camps. Acoustic sensors were calibrated while in Admiralty Bay.
2. Several equipment and logistic problems were experienced. Prior to sailing from Punta Arenas, a faulty CTD power supply was discovered. Sensors were removed and attached to the spare CTD and the faulty instrument was sent back to the manufacturer with the intention of having it repaired in time for Leg II. A shipment of C14 radioisotopes did not arrive before sailing and scheduled primary productivity experiments had to be cancelled. The barometer on the meteorological instrument package failed and the spare package was mounted on the ship's mast. The salinometer was DOA; two water samples from every other CTD cast are being saved for later salinity analysis. The lack of a spare CTD has forced us to be more conservative when deploying during heavy seas. As a result, CTD operations were cancelled at 3 stations.
3. Krill, salps and other zooplankton. Krill were present, primarily in small numbers, in 15 samples (60%). Most of the krill (1971 of 2215 total) came from three samples taken over the South Shetland Island northern shelves. Krill mean and median abundance values in the West Area were, respectively, 3X larger and 6X smaller than during the January 2001 survey reflecting less widespread (i.e., patchier) distributions this year. Lengths ranged from 18 to 60 mm with 48 mm the median value. The overall length frequency distribution represents a mixture of small juveniles (14%), intermediate sized immatures (19%) and large mature stages (66%). Mature females alone contributed over half of the krill collected; the majority of these (88%) were in advanced reproductive stages (i.e., with developing ovaries and gravid). The notable absence of spent females and larval krill indicate that peak seasonal spawning activity had not yet been initiated.
Salpa thompsoni occurred in all but one of the West Area samples (96%) and was represented by a wide length range of both aggregate and solitary forms indicating a long production period. Occurrence of aggregates 65-72 mm in length suggests initiation of chain production in mid-August 2001 which is quite early. Despite an apparently long production period, salp abundance was relatively low: mean and median abundance values (89 and 37 salps per 1000 m3) were an order of magnitude lower than those observed in the West Area during January 2001. Greatest concentrations were located in Drake Passage offshore of the island shelf areas.
Copepods were present in all samples and numerically dominated the catches. Mean and median copepod abundance values (16,000 and 12,000 per 1000 m3) were exceptionally large and indicated the widespread distribution of large copepod concentrations across the entire area. These concentrations were 3X and 10X greater than those observed in the West Area during January 2001. The pteropod, Clio pyramidata; amphipod, Themisto gaudichaudi; and larvae of the euphausiid, Thysanoessa macrura, were also exceptionally abundant.
4. Krill biomass and dispersion. The high diversity and abundance of crustacean zooplankton introduced additional uncertainties in the interpretation of acoustic return. Estimated densities of krill were highest over shelf areas, particularly along the southwestern most transects in the vicinity of Cape Shirreff. Overall krill biomass density for the West Area was estimated to be 11 g m-2 as compared to 17 g m-2 in this area during January 2001.
5. Phytoplankton. Chl-a in the upper 30 meters was 0.77 +/- 1.00 mg m-3. This is similar to the average values for the West Area last year (0.58 +\- 0.89 mg m-3 at 5 m depth). However, notable differences were observed. Stations located in waters less than 1000 meters depth had concentrations of 0.72 +\- 0.21 mg m-3 as compared with pelagic stations that had 0.83 +\- 0.34 mg m-3 (last year coastal stations had much more chlorophyll than pelagic stations). In this regard, of interest is that the highest chlorophyll concentrations this year in the West Area were located off the shelf in deeper waters (Stations A16-06, A17-07, A19-09 with >1.0 mg m m-3 in near surface waters). The optical oceanography component (funded by NASA to Greg Mitchell, SIO), provided satellite (SeaWiFS) images of surface chlorophyll distributions, as well as in-situ optical properties of the upper water column at 9 stations. This is being accomplished by deploying a free- fall in situ radiometer and by obtaining water samples at discrete depths for measures of: 1) particulate and soluble absorption, 2) pigment identification for phytoplankton diversity analysis, and 3) various other analyses to help describe microbial processes in the euphotic zone.
6. Oceanography and meteorology. The frontal region marking the merge of oceanic and coastal waters was delineated parallel to the continental shelf break north of Livingston and King George Islands. It was visible mostly on the outer edge of the transects between the last two stations, approaching closer to the coast in the north with a tongue of oceanic water intruding into the northeastern line of stations in the West Area. Weddell Sea water was apparent at the first station occupied in the western Bransfield Strait.
Predominantly Westerly winds with a
short period of NE on Wednesday. Strong (55 knts) variable winds were
experienced in Admiralty Bay on Monday, accompanied by a steep drop in air
pressure. The rest of the week varied from 5-38 knts, averaging 20& knts.
Air temperatures were moderate (0.3-3.6°C) with the average above 2°C.
It was mostly overcast with mist and rain, poor visibility and a few short
periods of clear sky. Humidity was high for most of the week except during
the brief sunny periods on Tuesday/Wednesday and Saturday.
7. Predator diet studies. Lipids were extracted from
16 fur seal milk samples and frozen. Net caught specimens of krill
(E. superba) and myctophid fish (E. carlsbergi) were also
retained for lipid extraction. Ten fur seal scats were processed
with many containing fish otoliths and krill carapaces. No squid beaks were
present. The krill carapaces were measured and there appears to be an equal
number of male and female krill in each scat. The myctophid fish otoliths
include primarily those of E. carlsbergi and
E. antarctica with a few from G. nicholsi. The scats with a
large number of otoliths had relatively few krill carapaces and chitin,
whereas the scats with a great deal of krill carapaces and chitin contained
smaller amounts of fish otoliths.