Midway through the broad-scale survey, when we came to Station #53, we were met by a host of icebergs that nearly blocked our passage to the station location. In the midst were many seabirds and seals, and a number of whales. In a layer 80 to 120 m below the surface was a dense acoustic scattering layer of what we thought were krill. Today (24 May), we returned to that site to investigate further the linkage between the occurrence of these predators and their prey. The weather for the study was ideal and we are just finishing up work at the site. Our current position is -68 47.089°S; -71 2.163°W. Winds are less than 10 kts out of the east (080) and the air temperature is -3.4°C.
Yesterday, our research was conducted in Lazarev Bay, which provided us with the possible opportunity for conducting bird, especially Adélie penguin, and mammal studies, and ROV studies of under ice krill abundance and behavior. We arrived in the Bay late at night and immediately began work with the ROV to study the distribution and abundance of krill living in the vicinity of the sea ice bottom surface. This work went smoothly, in spite of a number of seals that found the ROV a subject of interest, until the operation was brought to a halt by water leaking into the underwater housing. For the daylight operations, we were again in search of penguins and whales, but with the continuous pack ice in the Bay and the low possibility of finding whales present, the focus was on the penguins. Based on information from Bill Fraser, the Adélie Penguin expert on the R/V Gould, we decided to go deeper into the Bay where he said the ice was thicker and we might be able to get to an ice shelf where penguins were likely to come up out of the water around noon after having finished their daily feeding. So about 0900, we headed into the brash ice, which flowed around large icebergs distributed throughout the Bay. Along our route we did encounter Adélie penguins in ones or twos, occasionally more, but the unconsolidated brash ice they were on was too thick for the Zodiacs and too unstable for a person to walk on. So we could not get to them. Finally about 1300, we got to a point where there were too many icebergs to maneuver around and so we turned to start the trek back toward the entrance of the Bay. Along the route, we came past an immature Emperor penguin on a small flow. Also present in moderate numbers were several species of seals. Late in the day, the ROV was again deployed and a series of transects originating from a central point were run under the ice to access krill distributions. The nighttime was used to steam to the next station approximately 50 nm northeast of Lazarev Bay, shooting XBTs at 10 nm intervals along the route.
Eileen Hofmann reports that the CTD group had a quiet day working on hydrographic data collected during the survey. However, several breaks were taken from data analyses to enjoy the spectacular Antarctic day and wonderful scenery.
Susan Howard continued to provide ADCP-derived current maps for the transit to Lazarev Bay. These current distributions showed west-southwest flow along the inner portion of the continental shelf. This is consistent with the flow suggested by the hydrographic distributions.
After leaving Lavarez Bay, XBT drops at 10 nm intervals were resumed
and continued until reaching survey station 53. These will provide additional
temperature data inside of the inner-most portion of the survey grid near
Bob Beardsley's Drifter Note 143 (May 23)
A figure (not shown in this report) shows the drifter tracks for the period starting yd 132 through 140.5, the most recent update. The red asterisk at the head of each track is the last position, indicating the direction of the drifter motion. Blue circles are plotted every 2 days along each track. Unfortunately, the NBP wind sensors did not work well from roughly yd 138.5 to 139.5, so that we cannot estimate the wind stress during this period. Several drifters located to the west off Alexander Island moved rapidly towards the southwest down shelf during yd 130 to 140, perhaps being wind driven, but we can not investigate this more until a detailed analysis of the NBP and LMG wind data can be made.
Points to note:
1. Drifters 7, 8, and 9 continued to move deeper into Marguerite Bay. Drifter 7 appears to have moved to the coast, while drifters 8 and 9 turned towards the south and continued along the coast.
2. Drifter 10, which had entered the Bay earlier, moved quickly out of the Bay along the northeast side of Alexander Island, with a mean speed of ~25 cm/s.
3. After drifter 3 moved into the "iceberg graveyard" at CTD station 53 just off the tip of Alexander Island, it reversed course and moved northeast for ~2 days before reversing course again and moving very rapidly (with maximum speeds 40-50 cm/s) towards the southwest along the coast of Alexander Island, arriving off Lazarev Bay on yd 140.
4. The three drifters on the shelf northwest of Alexander Island moved down shelf towards the southwest, with speeds varying from ~10 cm/s for drifters 4 and 11 to 20-40 cm/s for drifter 2.
5. Drifter 5 continued to move slowly in a counterclockwise gyre, suggesting that this drifter has remained in a persistent eddy, perhaps tied to the local topography. The lack of significant movement of this drifter from its initial deployment position over many weeks is a real puzzle.
6. The drifter data collected to date suggests that there is surface
flow into Marguerite Bay around the southern end of Adelaide Island, with
return flow out of the Bay along the northeastern tip of Alexander Island.
The surface salinity data supports the idea of a relatively fresh coastal
current initially trapped to the topography exiting the Bay along Alexander
Island. We hope to deploy the additional drifters in the mouth of the Bay
to further test this idea of a clockwise surface circulation around the
Chris Ribic and Erik Chapman reported that on 23 May, while in Lazarev Bay for a day of bird, whale, and ROV operations, they spoke with Bill Fraser on the LM Gould about the penguin work he has been conducting in this area. He reported having found an uncharted island where penguins have been hauling out after foraging typically between the hours of 9:30 and 13:00. He said that he has had little luck getting to the penguins on the island and suggested looking further in the bay for more solid ice where the penguins may haul out and be more accessible for diet sampling. We began moving into the bay looking for penguins and heavy ice conditions, traveling through pancake and brash ice within dozens of large icebergs. The ice was too thick to zodiac through, but not thick enough to travel over without a boat. A few small groups of 2 or 3 penguins and several single penguins in this area were observed. They attempted to approach two penguins to see if they could either walk from floe to floe or be craned over the birds to reach the birds. They weren't able to capture the penguins, but look forward to trying again in King George VI sound in Marguerite Bay where Bill Fraser reported seeing hundreds of Adélie Penguins. In addition to the Adélie Penguins, they saw a very small number of Snow Petrels and Kelp Gulls, and also one juvenile Emperor Penguin.
Ari Freidlander reported on 23 May that no whales were seen during the circuitous transit through Lazarev Bay. However, 11 crabeater and 2 leopard seals were seen.
Neither BIOMAPER-II nor MOCNESS was deployed during 23 May.