Meteorological measurements for the Western Peninsula site of the Southern Ocean GLOBEC Study are very important to understanding the dynamics of the currents in the region and the atmospheric forcing on the upper water column. While good weather measurements are made while the research vessels are working in the area, there are no weather stations in the vicinity to provide continuous weather measurements that are representative of this coastal environment. So today we spent the daylight period installing an Automated Weather Station (AWS) on the largest island in a small group known as the Kirkwood Islands. We are currently about a ½ mile from the island at -68 20.495°S; -69 01.690°W (1300 local). The wind is out of the south (070) at 15 to 18 kts and the air temperature is -4.0°C.
Yesterday we worked in the vicinity of Station # 53, where we previously had observed many seabirds and seals, and a number of whales, and what we thought was a dense acoustic scattering layer of what we thought were krill 80 to 120 m below the surface. Humpback and minke whales were both heard (via sonabuoy) and sighted a couple of miles before reaching the station location, so we steamed back towards that site until we came across them. By about 1000, both Zodiac inflatable boats were away, one headed to where the whales were to try to get biopsy samples and the other went over to a patch of brash ice where there was an attempt to catch petrels and see what they were eating. The weather was ideal with no wind, little swell, and for most of the day a glassy sea surface. Visibility was excellent with high clouds overhead and the work on this day was done with the looming peaks of the mountains of Alexander Island and a large glacier coming down to the shore line just a few miles to our east. When we were here during the grid study, the clouds were down to the water and the mountains were not visible.
It was a good day for the whale group. Ari Friedlander obtained biopsy samples from three humpbacks and one minke whale during the Zodiac forays out into the still waters where the whales were diving amongst the scattered patches of brash ice. The bird people did not have as much luck. Chris Ribic and Erik Chapman went out to brash ice patches to try and trick petrels to come close to a oil soaked red cloth out on a piece of ice, so they could net them, but they were too quick and none were caught. They did, however, make some interesting biological observations as described below.
The Zodiacs were out of the water as the last of the daylight faded around 1515. BIOMAPER-II went into the water shortly after that (1530) at a location centered where the work with the Zodiacs had been done in order to map a subsurface layer of krill that we had observed earlier in the cruise. This work went until 2130 and was followed by a CTD. Around 2300, we got underway for the possible AWS deployment site.
Eileen Hofmann reports that because the focus of today's activities was on obtaining data for top predators, the CTD was not deployed during the daylight hours. However, several members of the CTD group did participate in the collection of bird and whale observations. Thanks go to Chris Ribic, Erik Chapman and Ari Friedlander for providing the opportunity for physical oceanographers to learn some biology.
After the bird and whale activities, BIOMAPER was deployed (see Wiebe
et al. report below). Following retrieval of BIOMAPER, a CTD cast was made
to obtain a data point for extending the depth range of the BIOMAPER observations
and to fill in the inner portion of the survey grid. After this CTD station,
the intent was to deploy XBTs along a transit that takes us to the eastern
end of Alexander Island. Once beyond the tip of Alexander Island, we intend
to do additional CTD and XBT deployments as we transited east-southeast
towards the Kirkland Islands. These data will provide additional coverage
of the coastal current that flows out of the southern end of Marguerite
Bob Beardsley's Drifter Note 144 (May 24)
A figure (not presented in this report) shows the drifter tracks for the period starting yd 136 through 142.5, 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.
Points to note:
1. The three drifters on the shelf northwest of Alexander Island continued to move towards the southwest. Drifters 2 and 11 reached peak speeds during yd 140-141, then have slowed. Winds during yd 140 were moderate (25-30 kts WSW), followed by generally weak winds (less than 20 kts).
2. Drifter 10 left Marguerite Bay along the northeast side of Alexander Island, then turned west and moved along the coast, following the path of drifter 3 roughly 2 days later. These two tracks illustrate the coastal current of MB water leaving the Bay. This flow appears to be partially buoyancy driven, carrying less saline water (S<=33.3) than that found on mid-shelf (33.3<S<33.6).
3. Drifter 9 continued to move clockwise along the coast in MB. It will be interesting to see if it exits the Bay following drifter 10.
The drifter data collected to date suggest 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 support the idea of a relatively fresh coastal current
initially trapped to the coast exiting the Bay around the northwestern
coast of Alexander Island down to Charcot Island.
Chris Ribic and Erik Chapman reported that, on 24 May, they attempted to diet sample Snow Petrels from a Zodiac in brash ice near Station 53. They parked the Zodiac in several different locations in the brash and baited the birds with red cloth soaked in cod liver oil. The birds were attracted to the bait, but they did not come close enough to the boat to b caught them with nets. The attempts were made in two types of brash ice; 1) Brash organized in discrete bands or "wind-rows," and 2) continuous, unbanded brash ice. Although no birds were captured, some interesting observations were made of the Snow Petrels and their association with the two types of brash as they flew low over the ice, occasionally landing to pick food from the water between pieces of ice. In particular, there were more birds and more feeding behavior in association with bands of brash than continuous brash ice cover. This agrees with a general trend in the association of Snow Petrels within ice that has been noticed over the course of the cruise. Perhaps by focusing on these conditions for feeding, the Snow Petrels are telling us something about physical and biological processes associated with this type of ice cover. One possible explanation could be that converging currents are concentrating surface brash as well as ice-related biota that are in turn, attracting prey for the Snow Petrels. In particular, planktonic larval krill in the upper surface layers could be concentrated by these processes. Further investigation of the physical and biological properties of these habitats could help illuminate these processes and their biological significance.
Ari Freidlander reported on 24 May that at first light the ship was
positioned near Station #53 off the north and west coast of Alexander Island.
Conditions were optimal for observing; overcast skies, little swell, and
minimal winds. Icebergs were scattered around and small patches of brash
ice covered no more than 1/10 of the visible area. Before arriving at station
in the late night, whales were spotted near the ship and were also heard
acoustically. The decision was made to turn back towards the known area
of sightings. Soon thereafter, around 0930, whales were sighted and preparations
were made to launch the Zodiac to obtain biopsy samples (68 44.655°S;
71 26.585°W). The whales were slowly working
back and forth along a three to four mile stretch perpendicular to the
coast, presumably feeding. The whales in the area were seen as a group
of three minke whales, a group of two minke whales, three pairs of humpback
whales, and a single humpback whale. Skin and blubber biopsy samples were
taken, via crossbow, from three humpback whales and one minke whale (only
1 sample was taken from each group of animals). Generally, the whales were
easy to approach. One group of humpback whales was left alone after a short
approach when it was clear that the animals were not fond of our presence.
Only one of the whales reacted significantly to the biopsy dart. This was
the final humpback whale sampled. This animal and another were seen logging
at the surface as we approached. When the dart struck the whale, it arched
and then raised its head out of the water before diving. This was more
than likely a startled reaction to the impact of the dart on the resting
whale. All in all, it was a tremendously successful day of biopsy sampling
and well worth the wait.
BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, S. Gallager and
As noted above, BIOMAPER-II went into the water at a location centered where the whales had been observed diving in a manner that suggested they were feeding. We hypothesized that the whales and seals (which were also present in good numbers) were feeding on a krill layer and our intent was to map out the krill concentrations in the area. Once BIOMAPER-II sensor systems were turned on, a target layer for mapping was quickly identified as being between 70 and 140 m. These were almost the same depth intervals as was observed for the intense backscattering zone seen during the broad-scale survey in this area more than a week ago. An N sampling design was used to guide the sampling. The N was oriented perpendicular to rows of brash ice that were present most of the day. Given the light winds, the rows of brash ice may have been caused by convergences and divergences driven by currents associated with the topography. The sampling was intended to see if there were correlations between the surface ice structure and the patch structure in the sub-surface layer. Each leg of the N was about 2 nm and the diagonal was about 3 nm. We ran the N twice with the ship moving at 3.5 to 4.0 kts; once with the BIOMAPER-II at 50 m to map the layer acoustically and once towyoing between 90 m and 120 m to gather VPR data as to the species composition of the layer. During the run back to the start of the N for the second pass, a single towyo down to 150 m depth was made to get a vertical profile of the water column above and below the layer. Along the survey line, the volume backscattering varied significantly in intensity as we moved over fairly intense patches of high backscattering and then in lower levels of backscattering. The Video Plankton Recorder camera got many images of large adult krill during the towyo in the layer confirming our suspicion that they were the dominant inhabitant of the layer and the likely cause of most the backscattering there. At the end of the experiment about 2130, a CTD was done to characterize the water column.
No MOCNESS tows were made on 24 May.