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