Weekly Science Report 3: LMG01-04 Southern Ocean GLOBEC

(Jose Torres, Chief Scientist)

Science days 12 May to 18 May inclusive

I. LMG 01-04

a. Mission statement:

Overall goal is to elucidate shelf circulation processes and their effect on sea ice formation and Antarctic krill distribution, and to examine the factors that govern krill survivorship and availability to higher trophic levels, including seals, penguins, and whales.

b. Projects represented on the process cruise

BG-232-0 Dan Costa and Jennifer Burns - seal ecology
BG-234-0 Bill Fraser - seabird ecology
BG-235-0 Chris Fritsen - SIMCO and water column phytoplankton communities
BG-236-0 Kendra Daly - Krill ecology and physiology
BG-245-0 Jose Torres - krill and fish ecology, krill physiology
BG-248-0 Meng Zhou - krill ecology, behavior, and modeling

c. Cruise overview to date

20 APR 01 LMG departed PA
24 APR 01 LMG arrived at KGI to pick up field party (O-196 :Dr. Brenda Hall) and began transit to Livingston Island.
25 APR 01 LMG arrived at Livingston Island. Lost a day to weather.
26 APR 01 dropped off Dr. Hall's team began transit to Palmer Station
27 APR 01 Arrive Palmer Station
28 APR 01 Depart Palmer Station for study site
29 APR 01 Began sampling at process station 1.
5 MAY 01 Concluded sampling at process station 1, transited to process station 5 and initiated sampling.
12 MAY 01 Concluded sampling at process station 5, transited to process station 4.
13 MAY 01 Arrived process station 4 and initiated sampling
17 MAY 01 Departed station 4
18 MAY 01 Arrived process station 2 and initiated sampling

d. Synopsis of process station 4

Process station 4 is located in the southeastern corner of Marguerite Bay and includes the entire George VI Sound. It is bounded roughly by the tip of Alexander Island vic 68.8°S 70.6°W on the NW, 68.8°S 70.0°W on the NE and the southern end of George VI sound on the south. It includes the southeastern end of the large cross-shelf canyon that runs SSE through Marguerite Bay. The canyon runs right down the middle of George VI sound. The LMG arrived at station 4 at about 1000 13 May in the vicinity of the Bugge Island group but wind and visibility prevented close inspection of the island. A trackline was developed for towing and two MOC 10's and two MOC 1's were executed on our first day of sampling. Each day thereafter the LMG spent the daylight hours surveying for seals and penguins and the night hours towing either MOC 1's , MOC 10's, or executing an ADCP/CTD survey down the length of the canyon to map current patterns. Nets were fished at two points along the length of the canyon. The southern end of the canyon was well sampled; depths were about 1000 m all the way to the perennial ice at the southern end of the canyon. There was little or no new ice in George VI sound and the coasts contained much brash and many grounded bergs More specific information is available in the individual group reports.

A few seals and numerous penguins were spotted but were inaccessible to our predator teams due to the character of the ice, which was largely unconsolidated glacial rubble. Station 4 was departed 17 May for station 2, which is located in the mouth of the bay on the canyon axis.

e. Individual group reports

1. BG 232-0 Burns/Costa
This week we did not have much success at sighting seals, and were unable to conduct any research. The few seals we sighted were deep in the pack ice and inaccessible by zodiac (n = 4) or sighted late in the day on floes too small to support the seal and us (n = 2). The oceanography has shown that the prey availability in this area is lower than that of the previous station. In addition, there has not been much suitable ice for seals in the area, as most of the ice we have seen has been either large icebergs or very small brash. We conducted a thorough search of lower George VI sound and the western coastline, and do not think that the seal abundance in the area is high. It is possible that there are seals in the area, but the low light and low suitable prey and haulout substrate makes it unlikely that we could capture any, even if more time for searching were available. We were able to obtain a few krill from this station for our fatty acid and stable isotope work on seal diets, but there were few fish caught in the trawls, and so we do not have any fish samples from this area of the Bay. In contrast to the (lack of) work in this area, we have been receiving data from the three seals we tagged last week by Wyatt Island. All three are now at the NE tip of Day Island and foraging in the same locations and to similar depths. The two seals we tagged on 5/11 both headed to Day Island on the evening of 5/11, which coincides with the clearing of the bay by wind (see 5/12 report). The seals are diving routinely to ~ 200m, which is just above the bottom (as determined from ETOPO 2) but are also spending time foraging at about 50 m. The area they are frequenting is characterized by a variable bathymetry and several deep holes. We are very interested in returning to that area to deploy the remaining 5 tags and to obtain some more detailed information about the prey field in the area. The area to the south has high prey abundance and did contain some suitable ice. Detailed Report: May 12th: We remained at Wyatt Island overnight, following our success on 5/11. However, it blew hard in the night, and in the morning as we rounded the North tip of the island, it became clear that the wind had blown the bay free of ice. The ship then circumnavigated the island, and headed to George VI Sound. May 13th: Arrived near George IV Sound in snow and fog, no possibility of seal work as we were in open water. May 14th: Heard from the Palmer that they had seen a large concentration of seals at the tip of Alexander Island, and a smaller concentration 2/3 of the way up the coast (west side of the Sound). So, during the day we searched for seals along the western coast of Alexander Island (from Damocles Point to Cape Brown in the north). Snow and low visibility hampered our search range, but we did not see any sea ice or any old ice of the sort seals seem to prefer. Daylight is low, so search hours were limited to 10am 3 pm. We saw no seals of any species, no whales, and only a few birds. The weather forecast suggested a large storm was on its way into the Bay and so instead of continuing north to the tip of Alexander Island (which would be exposed) the decision was made to head back down into the Sound. As daylight was waning, we crossed through a strip of brash ice that had crabeater seals hauled out. The floes were too small to work and the light was fading fast (3pm). We were encouraged to see seals in the area, and had high hopes for the search the next day. May 15th: The LMG conducted at CTD grid all day; no seal research or sightings carried out. May 16th: Searched the bottom of George VI Sound for seals from 10:30 am onward. Started at the Southeastern side near Niznik Island, and followed ice edge along bottom to west until it petered out at Marr Bluff. The ice was glacial in nature, and packed tightly against the ice shelf and coastline. The few seals we saw (1 leopard, 1 weddell, 2 fur seals, 3 crabeaters) were deep within the ice, and inaccessible by zodiac or the LMG. However, we did see a large number of Adélie penguins. The search track crossed several CTD stations, so we stopped our search activities twice to conduct CTD stations for Meng and Frank. This reduced our search time from 5 hours to 3 hours. May 17th: The ship repeated the cruise track from yesterday, this time looking for penguins. We looked for seals during the daylight, but again did not see any that were accessible (total count 2 fur seals, 3 Weddell seals, 1 crabeater seals, no whales). May 18th: In open water conducting trawls and CTD stations. No sea ice, no seals. Science work completed to date: Three SRDL tags deployed on crabeater seals. Krill and mysid samples collected for dietary analyses. Remaining science to be conducted: Deploy 5 SRDL tags on crabeater seals Obtain samples of fish species collected in trawls (Currently we have 3 Electrona and 4 Pleuragramma).

2. BG 234-0 Fraser
The GLOBEC seabird component aboard the Lawrence M. Gould had a mixed week. Generally poor to dismal weather conditions, combined with poor visibility due to decreasing daylengths, greatly limited all attempts to locate penguins in areas where our remaining instruments could be deployed and more diet samples obtained.  These failures have nevertheless been quite instructive in that the search for these predators has revealed some previously unknown patterns related to movements and migration and autumn habitat choices. On a more positive note, our previously deployed instruments are providing an excellent and informative database on Adélie Penguin feeding and haul-out locations, thus providing our first glimpses of how these predators respond to circulation and bathymetry in their search for prey.

3. BG 235-5 Stewart and Marschall (for Fritsen)
Water column samples were taken concurrent with CTD/Rosette deployment at or around local noon from depths of 0, 5, 10, 15, 20, 30, 50, and 100 m at PS #5 on 05/12, at PS #4 on 05/13-05/17, and at PS #2 on 05/18-05/19. Sub-samples were preserved for later determination of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), particulate organic carbon (POC), bacterial and viral abundance, and spectral-absorption by phytoplankton, filtered for on-ship determination of chlorophyll a (chla) concentration, and assayed for estimates of bacterial production and photosynthesis-irradiance relationships (PE curves, at 5 and 30 m only). Not all parameters were sampled/measured on each cast. Bacterial production rates and PE curves for PS #5 were obtained the week prior, and were consequently not obtained from 05/12 samples. Chlorophyll a concentrations at PS #1 and PS #5 stations averaged between 0.20 and 0.25 ug chla l-1 while chla concentrations in two new ice samples collected from Dog Leg Fjord at PS #5 were 3.7 and 4.95 ug chla l-1 . Rates of both bacterial and primary production at PS #4 were approximately 50-60% of those measured at PS #1 and PS #5. Bacterial production at PS #4 remains consistent throughout the euphotic zone but declines below 75 m. Production and chla data from PS #2 are not yet available. Strong winds and warm temperatures (above freezing) continued to inhibit large-scale new ice formation at PS #4. Newly-formed grease and pancake ice was observed only on 05/12; no ice was sampled. Perennial land-fast ice may be present in King George Sound (PS #4). Unfortunately, a persistent northerly wind led to the accumulation of large fields of brash ice that hindered observations of ice conditions along the southern and western shores of the sound. Process site #2 is free of ice.

4. BG 234-0 Daly
Euphausia superba at Process Station # 4 in King George VI Sound appeared to have shifted to an overwintering mode. Analyses for most experiments will not be completed until after we get back to our laboratories at our home institutions. A preliminary assessment, however, suggests that both larval and adult krill in this southern region have shifted to a lower metabolism possibly in response to the diminishing day length. During this past week, our group completed molting/growth, ingestion, and egestion rate experiments, and an assimilation efficiency experiment for larval and adult krill. Acoustic transects were curtailed to some extent due to high winds and many large ice bergs in the region. Acoustic data were collected with one 1-m2 MOCNESS tow and one 10-m MOCNESS tow. Two layers, about 55 m and 90 125 m, were detected by the 120 kHz system. Some individual targets were detected by the 38 kHz system at depths > 300 m.

5. BG 245-0 Torres
Five MOC 10 tows and four live net tows were executed during the occupation of station 4. Two MOC 10's were located a third of the way down the sound vic 69 15°S, two were located about halfway down vic. 69 25°S, one was at the southern end vic 69 47°S. Krill were captured in moderate abundance in the 0-50, 50-100, and 100-200 depth strata. Adults were mainly found in the 100-200 stratum, smaller size classes and Euphausia crystallorophias in the 50-100 and some larvae in the 0-50. Gross estimates of krill abundance at station 4 were about 10% of those at station 5. In the deeper tows executed at this station (200-500, 500-800 m) an oceanic fauna was present, including the lanternfish Gymnoscopelus, the bathylagid Bathylagus and the pasiphaeid shrimp, Pasiphaea scotiae . At the southernmost trawling site, a new eelpout was captured, Seleniolychus , as was the icefish Cryodraco . Pleuragramma larvae were common in the upper 50 m, but Pleuragramma adults were not captured. Overall, our trawls in the canyon here showed a decidedly oceanic flavor with moderate krill abundance in the upper 200 m. In addition to the work on distribution and abundance we completed 100 individual determinations of respiration and excretion on krill adults and larvae.

6. BG 248-0 Zhou
George VI Sound and its vicinity

1. Bottom topography
The bottom topography was surveyed during the whole study period in George VI Sound. The measurements indicate:
1) The canyon in George VI Sound is deeper than 800 m. It extends from the shelf of Alexander Island, west of Marguerite Bay, into the ice edge whose current location is at 69 54.00°S, far beyond the ice edge in 1973.
2) In the east side of the deep basin west of Bugge Islands, the topography varies dramatically. Sea mounts rises from 1000 m to 400 m or from 450 m to 50 m in less than a quarter mile.

2. Temperature and salinity fields
The temperature and salinity fields were surveyed by 23 CTD stations in the Sound and its vicinity. The deep water below 400 m in George VI Sound shows similar T-S feature of the deep water below 400 m on the shelf. CTD measurements show the permanent stratification between 150 and 400 m. The water within this layer is relative cooler and less salty than the water on the shelf, which indicates local influence. The winter water lies between 75-90m, however in some stations, the surface mixed layer water is even cooler than this layer. The salinity in the surface water is relatively low keeping the water column gravitational stable. In most of stations, the winter water layer formed last year has been eroded, which gives an indication of the arrival of the winter season.

The shelf water follows the deep channel into George VI Sound. At the center of the basin, the water is relatively saltier than surrounding water. Because the temperature variation is small throughout in the region, the density field is primarily determined by the salinity field. Associated with this feature of the denser water at the center, a clockwise circulation is measured by the ADCP. Oppositely, the water is less salty at the mouth of the Sound forming a low-density center, which leads to an anti-clockwise gyre.

3. Circulation
The circulation in George VI Sound is featured by these two gyres associated with two high- and low-density centers from CTD and ADCP measurements. Further north, the flow field is dominated by the clockwise circulation in Marguerite Bay. ADCP measurements show the westward flow between 69 10°S and 69 15°S. This flow bifurcates between 69 30°W and 69 40°W. One branch follows Alexander Island northward, and exits on the shelf slope. Another branch turns southward and then southeastward as a part of the gyre at the mouth of George VI Sound. A part of the flow intrudes into the Sound following the eastern shelf.

4. Meteorological conditions
The wind direction sensors were down on days 134 and 135. We thank Bruce Felix for spotting the problem, and then making ceaseless efforts to fix the problem.
Mean STD Min Max
Ta(C) -0.07 0.64 -1.70 2.41
Ts(C) -1.41 0.31 -1.76 0
R-humidity 95.14 4.76 73.69 99.62
Bar 997.3 3.3 987.9 1005.1
Surface Fl (volt) 0.78 0.10 0.65 5.86
LW Radiation (W/m2) 283.2 28.4 184.1 309.0

5. Zooplankton
Four MOC1 tows were conducted around Station 4 region. Samples show a significant difference in species composition between Stations 4 and 5. There were no adult E. superba adults caught in this area. Overall, samples show this is a biological active area. Large amounts of copepods and krill larvae and moderate amount adult krill were caught in every net tows.