AMLR 2004 Weekly Reports No. 4

AMLR 2004 Weekly Report No. 4

1 February 2004

1. Our current position is north of the South Shetland Islands en route from Cape Shirreff to Seal Island. The first survey of bio-oceanographic conditions in the vicinity of the South Shetland Islands was completed this week. An extensive field of large icebergs emanating from the northwestern Weddell Sea precluded access to the last three stations in the southeast corner of the Elephant Island Area. Only 6 out of 9 stations could be occupied in the Joinville Island Area, and none of the planned stations in the northwest Weddell Sea were possible. The field of icebergs also covered the southern half of the Bransfield Strait, forcing us to shorten the planned transects in the South Area by an equivalent amount+ADs- 16 out of 21 planned stations in this area were occupied. For the entire survey 93 CTD casts, 92 IKMT tows and 23 acoustic transects were conducted over 16 days.

2. On 29 January, we broke survey operations in the South Area and disembarked C. Hewes and S. Corsolini at the Copacabana field camp. They are scheduled to be picked up by the L.M. Gould on her northbound transit to Punta Arenas. While in Admiralty Bay, the acoustic system was successfully calibrated+ADs- data collected prior to the calibration is currently being reprocessed.

3. After finishing the survey on 31 January, we proceeded to Cape Shirreff. On 1 February, we recovered the buoy deployed early in cruise, deployed two additional buoys, set up data loggers at the field camp, offload lumber, recovered trash, disembarked R. Rowley, embarked M. Goebel and D. Krause, and began the transit to Seal Island.

4. Krill, salps and other zooplankton. Limited sampling within the Joinville Island area yielded few krill or Salpa thompsoni. However, the 6 samples collected here were rich in copepods, notably coastal species, Metridia gerlachei, the high latitude salp, Ihlea racovitzai, and euphausiid, Thysanoessa macrura. In contrast, krill and Salpa thompsoni were frequent and at times abundant components of the South area samples and, along with M. gerlachei and T. macrura, numerically dominated the zooplankton there. Ihlea racovitzai were sporadically collected in the South area but they were quite abundant at several stations in the southern portion of Bransfield Strait. South area krill were primarily 30-40 mm in length and dominated by immature stages resulting from the 2001-2002 year class. These differed markedly from krill in the West and Elephant Island areas which were primarily mature stages, 40-50 mm in length, representing the 2000-2001 year class.

5. Krill biomass and dispersion. Mean krill biomass densities for the West, Elephant Island and South Areas were 29, 40 and 14 g m+AF4--2 respectively. This compared with estimates of 27, 22 and 11 g m+AF4--2 for the same areas in 2003. Mean krill biomass density for the Joinville Island Area was 13 g m+AF4--2+ADs- however this area was not surveyed during the first survey of 2003. Overall survey mean (weighted by strata area) was 30 g m+AF4--2 versus 21 g m+AF4--2 in 2003 for comparable areas. Krill biomass densities were highest over the shelf and shelf break areas north of the islands, particularly northwest of Elephant Island and north of Clarence Island.

6. Phytoplankton. Higher chl-a values were mapped along the shelf and shelf break regions of the Elephant Island Area as well as at the north-central and northeastern portion of the Area, which is part of an eddy that develops annually. Average 5m chl-a for the entire area was 0.69 +-/- 0.48 mg m+AF4--3 (integrated to 100 m was 44 +-/- 23 mg m+AF4--2). Highest chl-a concentration was found at station 02-03 (northeastern portion of the AMLR survey grid) having values of 1.85 mg chl-a m+AF4--3 at 5 m with integrated chl-a (to 100m) of 88 mg m^-2. Stations 02-01 through 02-04 were four of the five highest chl-a concentrations in the entire Area, with station 03-04 (northeast of Elephant Island) among them. Lowest chl-a concentrations were found at stations 07-02, 08-02 and 09-02, with 5 m concentrations +ADw-0.1 mg chl-a m^-3 (integrated values to 100 m were +ADw-15 mg chl-a m+AF4--2). In the Joinville Island Area and South Area surface Chl-a values were measured to be in the median range of 1 mg m+AF4--3 with a high station at A0609 of 1.55 mg m+AF4--3. Water samples were filtered for particulate, detrital, and soluble absorption spectra, CHN analysis, and MAA and pigment HPLC analysis at 34 out of 93 CTD casts. Comparison of the particulate absorption coefficient (ap) at 675 nm measured in the lab to the measured fluorometric Chl-a was in very good agreement with published values with a correlation coefficient of 0.98. Optical profiles were collected at 17 of the 34 sampled stations dispersed through the survey area with an IOP (Inherent Optical Properties) sensor package. These data include absorption and attenuation coefficients at 11 wavelengths, backscattering coefficients at 8 wavelengths as well as PAR, fluorometer, and CTD data. When weather permitted, under waterlight field data were collected at 12 stations (10 of which coincided with the IOP data) with a free fall radiometer collecting downwelling irradiance at 6 wavelengths in the visible as well as PAR and upwelling radiance at 7 wavelengths in the visible.

7. Oceanography and meteorology. 36 CTD stations were occupied in the Elephant Island, Joinville Island and South Area. Zone 2 waters were predominant around the eastern part of the Elephant Island Area, with an eddy of Zone 3/4 water around Station 04-03. In the Joinville Island and South Areas, Zone 4 and 5 waters were found with the inshore stations of the South Area having surface waters (0 to 50 m) with lower salinity and higher temperatures. A notable meteorological phenomenon occurred on 28 January, when the barometer rose 16 mbar (from 977 to 993 mbar) in 4 minutes. The ship's bridge barometer experienced a similar jump. The week saw winds predominantly from the northwest averaging 15 to 20 kt, with Thursday and Friday seeing light north-easterlies, averaging 10 kt. Also of interest was the rapid increase in the thermosalinograph's surface salinity 33.86 to 34.18 PPT, with a concurrent drop in SST from 2.5 to 0+ALA-C, between Stations 06-09 and 06-10, in the northwestern Joinville Island Area.

8. Predator diet studies. All milks samples have been processed for Leg I. All scats from weeks 1-4 have been processed and 15 additional scats have come aboard and will be processed over the next 10 days from weeks 5 and 6. 23 myctophid fish have been measured, weighed, sexed and dissected for stomach fullness and content. Otoliths from each fish were removed and saved for a mytophid otolith guide. 305 krill (either frozen or live) have been sexed, and measured for total length, removed carapace length and width for a krill length validation study.

9. Bird and marine mammal observations. 20 species of seabirds were recorded in the vicinity of Elephant Island, and 15 species in the South Area. Greatest penguin abundance was observed on the east side of Elephant Island. Chinstrap penguins numbered in the thousands, interspersed with small groups of Macaroni penguins (group size: 8-10). Black-bellied storm petrels (hundreds heading south-west) and Antarctic fulmars (hundreds in rafts) were most abundant near Aspland and Gibbs Islands. Antarctic petrels (N+AD0-14) were observed foraging with Wilson's Storm Petrels and Antarctic fulmars. Two Royal albatrosses were observed while on station near Clarence Island (M. Force). The following marine mammals have been observed during this portion of our surveys (in order of abundance): Cetaceans: Humpback (adult and juvenile), Fin, Minke, Killer, Southern Bottlenose, and Right Whales+ADs- Pinnipeds: Antarctic Fur Seal, and Leopard Seal. Fur seals were observed in small groups (2-5) in the offshore waters of the Elephant Island transects. Highest counts observed for AMLR04 were recorded in the northeast corner of the Elephant Island Area. Upon leaving Admiralty Bay on 29 January towards station 10-10, four killer whales were observed (one adult female, two juveniles, and one adult male).

Submitted by Roger Hewitt