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, initiated sampling
d. Synopsis of process station 5.
Process station 5 was occupied as the second process sampling site to maximize the probability of encountering predators: penguins and seals. It was clear from satellite images and the SST that the probability of seeing pack ice was very low and we still needed to get some predator data. The logic was that if we couldn't get ice, at least we could get a rocky shoreline or calved-off bergie bits with a reasonable chance of access to crabeater seals and penguins. Also, our krill groups had some good trawling locales within striking distance of any predator concentrations that came to light.
Our strategy paid off reasonably well. We wended our way up Laubeuf fjord, which is the main channel that runs to the east of Adelaide Island. In the northeast corner of the channel that runs around Wyatt Island we found some crabeater seals. The Burns seal team had a good day instrumenting and working up seals. Unfortunately, no penguins were to be found. To get access to penguins we transited to Avian Island, which is just south of Adelaide, in the hopes that we'd find some Adelies for Bill Fraser and Chris Denker to work with. The weather held off just long enough after our arrival at Avian Island for Bill and Chris to get ashore and instrument and lavage a few penguins. We got a good full day of work done there and then shot back up toward Pourquois Pas Island and Bourgeois Fjord to explore for seals and penguins, but that turned out to be barren of predators. In the interim, during dark hours we were successful in getting at least a MOC 10 and MOC 1 every night, an ADCP survey every other night, and ADCP surveys during weather bad enough to preclude any other data collection. As a consequence, we have mapped process station 5 quite well. In addition, we have multiple tows in close proximity to predator concentrations.
Our concept of process station 5 as it evolved through our sampling is as follows. It is bounded on the south by the southern tip of Adelaide Island to include Avian Island; the southern boundary extends east to the continent. It is bounded on the north by the northern end of Wyatt Island and the channel that runs around it. Included within station 5 are the many fjords and islands that occupy the area between the east coast of Adelaide and the peninsula.
After a few PI discussions and assessing a couple of critical factors,
notably daylength and ice cover, or lack thereof, we decided to head for
our original site 4 in the vicinity of George VI Sound for the same reasons
we went to site 5. It is the best bet for everyone getting the data they
need. We have the head of the canyon right there for night ops and testing
our faunal concentration hypothesis and we have some islands near the canyon
for penguins and seals to hang out at. Also,
it is a pretty likely spot for ice formation.
E. Individual group reports
1. BG-232-0 Burns/Costa
May 5: we completed our testing of the PTTs that we will deploy on crabeater seals in the hopes of deploying tags once we were on site at Process Site 5. However, May 6 was snowing and windy, and so we were unable to conduct zodiac operations. We moved further north up Laubeuf Inlet in the hopes of finding calmer seas, some protection from the wind, and some ice. It is clear that there will be little sea ice in the region, but we are hoping that the seals haul out on shore or on glacier ice. May 7 :we deployed our first PTT on an adult female crabeater seal. We left the boat at ~9:00am and worked our way in north up the Lawrence Channel (east side of Wyatt Island) looking for seals. We immediately saw Antarctic fur seals hauled out on the southeast shore of Wyatt Island and as we moved north up the channel saw more and more fur seals (mainly on the shore of Wyatt and Arrowsmith Penninsula), and then some Weddell seals on small flows in the channel itself. Towards the head of the channel we saw many crabeater seals, and moved through the brash ice to a small floe, where we caught an adult female at ~11:30am. We had planned to do a reduced suite of measurements on this animal to get the feel for working on small floes and with gas anesthesia, which has never been used on pack ice seals before. The anesthesia went very well, and we successfully deployed our first PTT. We hoped to return to the bay the next day as there were many crabeater seals around, and this was the first location where we had seen any. Unfortunately May 8, the weather was poor, with high winds from the northeast and large waves. We remained on board, and planned for our work the next day. May 9: we searched the area around Avian Island for crabeater seals while Bill Frasier's team worked on Adélie penguins. We saw many southern elephant seals and Weddell seals hauled out on Avian Island and a few crabeater seals were spotted in the water, but we saw none on land. On the adjacent shore of Adelaide Island there were many southern elephant seals, but the nearby reefs were awash, and so we were unsuccessful at finding crabeater seals. Large swells prevented our searching further, or working far from the vessel. May 10: the boat moved northeast up Bourgeois Fjord, and at first light we were at the north end of Ridge Island. For once, the sky was clear, wind was low (15), and temperatures warm. We (seal team plus Frank Stewart and Skip) headed off the boat at 9am and went west between Blaiklock and Pourquoi Pas Islands. Saw one minke whale and the odor and mess of a shag or penguin rookery. The narrows were full of old ice (large bergs) but no sign of seals or sea lions on beach or ice. Got to the inlet on the S. Side of Blaiklock before the wind turned us back. Then headed north up the fjord along the side of Blaiklock, but did not make much headway against the wind and chop, and decided to move back downwind, as there were no sign of seals in this region either. Searched along the West side of the low tip of Ridge Island, and then cut across to Dog Leg Fjord. The fjord was calm and filled with brash ice and larger berg bits,and Frank was able to collect some new forming ice, the first we had seen since May 7. We spotted 3 crabeater seals on very small floes, and far in towards the bay. The heavy packed ice made it difficulty to work in very far, as ice hampers the zodiac. The first seal we approached entered the water while we were moving in, the second was too deep into the fjord and ice to reach, and the third was on a very small floe (8x10 m). We were able to get the seal in the net, but it escaped into the water before we could secure it. So, with no other seals in the area, we headed back across the channel, and down the East side of Ridge to the boat. Dog Leg Fjord looks to be a good site for seals protected bay and old floes. A good site to examine next season. Blind Bay might also be good, depending on the wind. We were unable to check it because the NE wind made the approach in a zodiac difficult. We were all cold and wet by the time we got back to the boat. May 11: we returned to Wyatt Island, since it has been the only place were we have seen a plethora of pinnipeds. Today was no exception. The wind was high, but the Captain was willing to navigate along Hinks Channel (no previous sounding) to get us in to the bay at the northeast end of Wyatt. Here we found many fur seals and crabeaters, and saw several minke whales. The winds that have been plaguing us had moved several large icebergs out of the bay since we were last here, but there seems to be a current pattern that retains ice in this area. The first animals we saw were the fur seals, but as we moved deeper into the ice, we saw several crabeaters on floes, and many more in the water. We launched the zodiac, and were able to rapidly deploy 2 PTTs: one on an adult male and one on an adult female. Each deployment took about an hour and a half, and the last one went very smoothly. The wind packed the ice together, and after the second seal, we were losing light, and the remaining visible seals were deep within the packed floes. We returned to the boat (3:30 pm) to work up the samples collected. It seems to us that the crabeater seals were hauling out in the morning, and then late afternoon most of the seals we saw were in the water. This suggests nocturnal feeding, and we are anxious to retrieve data from the tags we deployed. We were able to reconstruct the movements of the female we tagged on May 7. She spent a few days working along the coast of Arrowsmith Peninsula, and then moved north to the northeast corner of Day Island (the top of Hinks Channel). That area is very similar geographically to the area we have been working (although we have not been there yet), and it looks to be a likely spot to look for seals in the future. The dive data we have recovered from that female shows that she is spending a lot of time in the water, and making a reasonable proportion of dives between 100-200 m. This is the depth where the net tows in the area are finding lots of krill, mysids, and fishes. By remaining in this area and working here, we have been able to document (for the first time) the diving and movement patterns of a seal and the depth distribution and abundance of its prey. This is very exciting. She also appears to be spending most of her time near shore. As this is where all the remnant floes are, it seems that she is preferentially using areas where there is suitable ice for haul-out.
2. BG -236-0 Fraser
The GLOBEC seabird component aboard the Lawrence M. Gould had a most successful week. Working in calm waters greatly facilitated the analysis of Adélie penguin diet and scat samples collected at Palmer Station since October 2000. This aspect of our GLOBEC work couples directly with the activities of the Palmer LTER as we seek to obtain a continuous seasonal record of Adélie penguin diets in the sampling grids shared by these two programs. After a long search, we were also finally successful in finding Adélie penguins in the Marguerite Bay region. Finding these birds gave us an opportunity to deploy five of the 10 satellite tags we are carrying with us. We were also able to obtain 10 diet samples from birds recently emerged from feeding at sea and collected the scats of 20 birds that had overnighted at the sampling site. We are currently receiving excellent data from the satellite tags deployed in Marguerite Bay and also from tags deployed earlier at Palmer Station.
3. BG-235-0 Stewart and Marschall (representing Fritsen)
May 5 was spent in transit to process site #5 at the northern end of Marguerite Bay. Following arrival at PS#5, CTD casts were conducted daily at or around local noon from 05-06 to 05-10. Vertical profiles of CTD parameters (in vivo fluorescence, irradiance (PAR), salinity, and temperature) extended to maximum depths ranging from ~300 m on 05-09 to ~840 m on 05-06.
Water column samples were taken concurrent with CTD/Rosette deployment
from depths of 0, 5, 10, 15, 20, 30, 50, and 100 m. 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 concentration, and assayed for estimates of bacterial
and photosynthesis-irradiance relationships (PE curves, at 5 and 30 m only). Not all parameters were sampled/measured on each cast. A thermocline was well developed at a depth of ~80 m at the deepest station (~840 m) surveyed. At other locations a thermocline was poorly developed and water temperatures increased gradually from -1.2 to -0.6°C at the surface to ~1 to1.2°C at the bottom. Fluorescence at all stations was elevated in the euphotic zone relative to waters below ~80-100m. The rate of bacterial production was estimated across the range of sample depths at one station (05-06) and at 5 and 30m at two additional stations (05-07 and 05-09). Production rates fluctuated little from 0 to 50 m but were noticeably depressed at 75 and 100 m. Temperatures above freezing and a strong north-northwesterly wind seemingly prohibited the formation of new sea ice in most regions of PS#5. Grease ice was observed from the ship during a period of calm winds on 05-07, and, in concert with Zodiac operations supporting BG-232-O (Burns), was sampled from the sea surface in a protected area at the mouth of Dog Leg fjord on 05-10. New-ice samples were processed for later determination of chlorophyll concentration, bacterial and viral abundance, and dominant algal taxa.
4. BG-236-0 Daly
Process Station #5 has been a study in contrast relative to Process Station #1. Laubeuf Fjord has large concentrations of larval Euphausia superba, as did Process Station #1. However, the larvae in this picturesque fjord are primarily late stage furcilia (F5 and F6), whereas the larvae on the outer shelf were a mixture of calyptopis, early furcilia (F1-2) and some later furcilia stages (F4-6). The larvae in the fjord are also somewhat larger at the same stage than those on the shelf. The relative size differences suggest that the fjord is a more favorable environment for larvae, assuming that they have been in this region for some time. In addition, Laubeuf Fjord has large concentrations of large krill (juveniles and immature females and males), fishes, mysids, copepods, and amphipods. Other euphausiids, Euphausia crystallorophias and Thysanoessa macrura, are also present. During this past week, we measured growth and molting rates, ingestion rates, egestion rates, and assimilation efficiency in both furcilia and large E. superba. All stages are lively and actively feeding. The adults have sequestered lipid for overwintering.
Acoustic data were collected during 4-10 m2 MOCNESS tows, 2-1 m2 MOCNESS tows and 1 Tucker trawl. Diffuse layers near surface appeared to be larval krill. Deeper dense layers and individual targets were detected at the same depths where large krill and fish (e.g., Pleurogramma) were collected in nets. We also calibrated the acoustic system using a standard tungsten carbide sphere. The target returned sound intensity on the 38 kHz frequency was close to the theoretical value, while the 120 kHz system was about 3 dB hot. The difference in the efficiency of the 120 kHz transducer will be adjusted in the post-processing of data.
5. BG-245-0 Torres
The physiognomy of the catches has changed fairly radically from the shelf break to the site 5 area. The most obvious change has been the presence of large numbers of adult krill in the 50-100, 100-200 depth strata. Some new species have made an appearance, notably the mysid Antarctomysis ohlinii. It is the dominant species in the 200-300 m depth stratum and is very abundant in the 300-500 m stratum as well. Pleuragramma antarcticum has become the dominant fish and we are finding it from 50-500 m, with more individuals generally in the 200-500 m depth range. Pareuchaeta has become a major player in the upper 100 m and krill furcilia, while present, are not nearly as abundant as at the shelf break.
The euphausiid, Euphausia triacantha, a dominant at the shelf break, is completely absent from our catches at station 5 as are other members of the classical midwater fauna including Gnathophausia, Gigantocypris, and the coronate scyphomedusa Periphylla. At a couple of the station 5 trawling sites we have picked up considerable siphonophore biomass at the 200-400 m depth range, and in one, we picked up a huge swarm of thimble jellies in our 200-300 m net.
6. BG-248-0 Zhou
Both ADCP echo intensity measurements and MOC-1 tows showed significant gradients between Station 1A (66 5.9°S, 71 3.7°W) off the shelf break and Station 1B (66 5.7°S, 70 59.3°W) on the shelf. In ADCP measurements, the vertical structures are similar, but the strengths are different between Stations 1A and 1B. The strongest backscattering layer is centered at 200 m with a thickness of 100 m; and a surface layer, which is relatively weak. The catches of MOC tows at Station 1B are at least 10 times more than those at Station 1A. In all hauls, there are large amount of yellow-greenish stuffs, like green grass under microscope (excuse my biology) though the fluorometer measurements did not show any significant change in fluorescence concentration (voltages) between Stations 1A and 1B.
We had to abandon our plan to run a transect following the deep canyon into Marguerite Bay during our transit from Study Sites 1 to 5 because of the heavy sea. Captain took a short direct transit from our shelf break station to the south of Adelaide Island, and took Woodfield Channel into the north end of Marguerite Bay, the entrance of Laubeuf Fjord. The transect provided a view of the contrast from patchy mid-depth aggregations and a weak surface layer in blue water on shelf regions to very dense near surface aggregations and mid-depth aggregations in Marguerite Bay. MOC-1 tows, similar to MOC-10, caught very large amount of E. superba adults and larvae in the deep channel at the entrance of Laubeuf Fjord (68 3.7S, 68 3.1W). In a MOCNESS tow, we typically find:
25-50m: few adults and mostly
50-100m: A lot E. superba adults (5-6cm)
100-200m: A lot euphausiid larvae, some E. superba adults.
The ADCP is mounted approximately 4 m below the surface. The bin length is set 8 m, and the blank after transmitting is 8 m. From these settings, the center of the first measurement is at 14 m, which should be an integration between 10 and 18 m. We missed the first 10 m close to the surface. Because E. superba adults were caught between 50-150 m, the ADCP echo intensity measurements should not miss swarms of E. superba adults.
The cross talking between OPC and MOC1 has been greatly reduced by reducing SFK voltage on the OPC from 6 v to 1 v. The OPC behaves normally; and MOCNESS communication quits very occasionally. The MOC1 has been working normally. We should thank ETs, Sheldon Blackman and Bruce Felix, for their tireless efforts to solve these problems.
The meteorological data collected on the Palmer and Gould were compared for the period when they met. The long wave radiation measurements on the Palmer and Gould show a difference of 25 W/m2 during the period both of them were at Palmer Station. The comparison for the period when they met in Marguerite Bay shows a difference of 50 W/m2.
The mean meteorological parameters for the period from 5/5/01 to 5/10/01 when the Gould is in the vicinity of Station 5:
|Surface Fl (volt)||0.90||0.17||0.58||1.18|
|SW Radiation (W/m2)||3.40||7.9||0||74.8|
|LW Radiation (W/m2)||245.0||24.6||158.7||290.0|
|Net Radiation (W/m2)||-59.1||25.6||-123.4||24.5|
These parameters are calculated after applying a 60 min lowpass filter to the 1 min met data.
The water below 200 m in the deep basin at the entrance to Laubeuf Fjord show the same TS characteristics as the water below 200 m on the shelf. The temperature of the surface mixed layer is similar to the surface water on the shelf, but it is much fresher. The temperature and salinity in the mixed layer are .547°C and 33.363 ppt, respectively. The mixed layer depth is approximately 70 m. The temperature and salinity in the deep water below 250 m are 1.151°C and 34.624 ppt, respectively. Moving further into Laubeuf Fjord, the TS signature west of Wyatt Island is similar to that in the deep basin at the entrance of Laubeuf Fjord. However the mixed layer is shallow, approximately 50 m and the temperature is 0.12°C cooler.
The CTD cast at 67 7.6°S, 68 9.3°W right south of Adelaide Island, just west of the entrance to Laubeuf Fjord, shows different TS characteristics. The surface temperature is .17°C, and the salinity is 33.045. The upper water column is continuously stratified. The water column between 175 m and bottom (~300 m) is very uniform. The temperature is 0.238 and salinity is 34.258 ppt, which indicate the water is much cooler, fresher and lighter than the water at the entrance of Laubeuf Fjord.
1. The entrance to Laubeuf Fjord
The ADCP survey over the deep canyon shows a mean southward flow of 20-40 cm/s at all depth. There are northward currents of 5-10 cm/s at both sides of the deep canyon. The survey took over 11 hours, and covered an area of 15x15nm2. We did not see any reversal current in the deep canyon. The lack of vertical structure in currents suggests the current is mostly barotropic. The survey also covered almost a semidiurnal tidal period in the first survey. The measurements show a persistent southward flow in the deep canyon. This current has been repeatedly measured in the period we stayed.
Corresponding to the current around station 5A, the E. superba adults are concentrated in the depth of 50-150 m and a horizontal scale of 2-5 miles. Relatively more aggregations are founded at the slopes at the sides of the deep basin where currents are relative weaker or revered to the northward. Such relation may indicate a retention mechanism for krill to remain in this area. Of course, this is very preliminary. More detailed data analyze will be conducted.
2. Transect along the principal axis of Laubeuf Fjord and Cole Channel
ADCP transects made along the principal axis of Laubeuf Fjord and Cole Channel show a mean southward flow plus a near tidal period oscillation (This is very rough view from moving ADCP data). The ADCP echo intensity transect shows a spatial variability of krill distribution. The largest E. superba swarm of 20 nm along the fjord is located in Laubeuf Fjord, east of Rothera. The abundance of E. superba adults is still abundant in the area west of Wyatt Island, but relatively reduced and patchy. For example, right after MOC10 tow which caught a lot E. superba adults, MOC1 almost did not catch any E. superba adults along the same track MOC10 did. The processed the ADCP echo intensity data show us that we just missed the swarm during the MOC1 tow.
It is not known whether E. superba adults have diel vertical migration behavior. We saw evidence that the backscattering layer occupied by E. superba adults moved deeper from 75-100 to 150 m, or simply disappeared in the mid-layer typically occupied by euphausiid larvae in morning. It is hard to interpret such change because the change can be produced by spatial variability, current advection and vertical migration. Whether E. superba adults vertical migrate between day and night needs to be further investigated.
3. Laubeuf Fjord, east of Rothera
Several ADCP transect show the highest abundance of E. superba adults. The aggregations of E. superba adults were found mostly on the slopes of the deep channel where currents were relatively weak or northward. An ADCP/XCTD survey was abandoned in the mid because the ship might need more time to transit to Wyatt Island under heavy wind condition. Ten XCTDs were launched, 5 were bad.
4. West of Wyatt Island
The current in this portion is more like estuarine circulation, one surface southward flow and a deep returning flow. E. superba adults are abundant, but less than Station 5A and 5B. The patch size is also reduced to a 1-2 km.
5. Bourgeois Fjord south of Pourquoi Pas Island
MOCNESS tow samples show there is a huge amount of salps, mysis and large copepods below 150 m. The codends were overfilled. The ADCP shows a weak vertical uniform oscillation flow, which suggests the barotropic tidal currents.