4, 5, and 6 May 2001
N.B. Palmer

Today (May 7th), we were greeted by a magnificent sunrise and a grand view of the Western Peninsula's mountains coming right down to the eastern edge of Marguerite Bay with its snow fields and I presume glaciers. The sun, still not quite up at 10:00, backlit the mountains giving them a golden halo in the region of sunrise. The air feels cold, although it is still right around 0°C and there is ice on the helicopter deck - frozen melt water from the snow of the last few days. Because of the calm seas, the aft main deck is now dry - no water sloshing back and forth as usually is the case. The wind is out of the northeast (075 degrees) at 10 to 15 kts. We are now at -68 37.753°S; -67 52.891°W (10:25 local - 7 May) and headed to Station # 33.

During May 4th, the weather was really foggy and wet. The temperature hovered around freezing and snow was melting on the upper decks of the ship and the melt water was running over their edges, splashing on the lower decks. None of the edges of the ship seem to have good drains. The wind picked up again too and the seas began to build up from the relatively calm conditions of yesterday and to some extent the day before. A light snow was off and on all day and usually it came on stronger at night. We completed work at Stations 20, 22, and 23, which were deep stations off the shelf or at the shelf break. May 5th started out cloudy with low visibility, but the sun broke through the clouds and with moderate winds, it was a welcome change from the previous days overcast and snow. During the evening, snow again fell. During the course of this day, work was completed at Stations 24, 25, 26, and 27. May 6th also started out with moderate winds and low visibility, but as we steamed into the area south and east of Adelaide Island around mid-day, the clouds lifted to expose more and more of the rugged coastline of the Island and the Western Peninsula. as we approached Station 29 around mid-day. Black rock outcropping from snow and ice blankets which covers most of the earth here provided a stark contrast. Shortly before coming onto station 29, we steamed past an iceberg, the first actually seen on this cruise. We completed work at Station 28, 29, and 30.

Late in the afternoon of May 6th, a zodiac was launched from the R/V Palmer to carry a party of six over to the R/V Gould. A spare MOCNESS underwater unit on the Palmer was "loaned" to the Gould to replace one that had stopped working. And in return, the Gould sent back some other parts that were needed on the Palmer. Later in the evening, a second rendezvous took place to pick up another spare part from the Gould, this time one needed for the repair of the echosounder in BIOMAPER-II.

Eileen Hofmann and the CTD group reported that on May 5, they had completed 21 stations and four full survey transects. Few problems have been encountered with the CTD casts. The continued acquisition of quality data is due in large part to the efforts of the Palmer MT and ET personnel. Their efforts are much appreciated.

At the outer end of the fourth transect, we crossed the southern boundary of the Antarctic Circumpolar Current, which is indicated by water temperature at 200 m of 2°C. Based on this we decided to drop the most offshore station on transect 5 (station 21). The CTD cast at the outer station on transect four (station 20) was to about 3300 m. This cast showed Lower Circumpolar Deep Water at depth. Other water masses, such as South Pacific Deep Water and Weddell Sea Deep Water were not encountered.

Between stations 20 and 21 the CTD group did a XCTD drop which indicated that we were at the offshore side of the southern boundary of the ACC. This was confirmed by the CTD cast at station 22, which is the outer station on the fifth transect. We are now steaming inshore along this transect and will use XCTD casts in between the CTD casts to characterize the spatial extent of the southern ACC boundary.

The horizontal distribution of the temperature maximum below 200 m shows clearly Upper Cricumpolar Deep Water flooding the continental shelf throughout the northern part of the study grid. The axis of the onshore flow seems to be aligned with the canyon that extends from the shelf break across the shelf and into Marguerite Bay. A large meander of the southern ACC boundary is overlying the northern portion of the study grid and is providing the source of the Upper Cricumpolar Deep Water that is flooding the shelf.

It is encouraging that the hydrographic structure of the west Antarctic Peninsula shelf waters is similar to what was suggested during planning of the SO GLOBEC cruises. A preliminary look at some of the biological distributions suggests that these are following the water mass structure.

Bob Beardsley has now gathered enough meteorological data since the beginning of the cruise to put together a synopsis as a May 6th Met report.

Surface Cooling

The NBP left Palmer Station about noon (local time) on April 28 (yd 118) and headed west onto the shelf and south to the SO GLOBEC study area to begin the large-scale physical/biological survey. Over the next six days, the NBP sampled the shelf region between Adelaide Island and the upper slope until on May 6 (yd 127), the survey track line took the NBP into Marguerite Bay. This is a brief summary of the mean surface forcing conditions over the shelf during the six days (yd 119-125) when the NBP made five cross-shelf transects.

During this period, the winds were mostly southward and eastward, with speeds varying from near zero to a maximum of 22 m/s (~44 kts). The mean wind was 7 m/s towards 128T (SE), with an average scalar wind speed of 10 m/s (~20 kts). The mean air temperature was -0.9°C, mean SST was -0.6°C, and the mean relative humidity was 92%. The skies were mostly overcast, with periods of fog and snow flurries and little direct sunlight.

The shipboard met measurements were used to estimate the surface wind stress and heat flux components. The mean wind stress was 0.11 N/m2 directed towards 132T (SE), closely aligned with the mean vector wind. The net surface heat flux (Qnet) is composed of four components, the net shortwave radiation flux (Qsw) and net longwave radiation flux (Qlw) and the two air-sea flux components, sensible heat flux (Qsen) and latent heat flux (Qlat). The mean and standard deviations of Qnet and the four components for the six-day period are given in units of W/m2 in the following table:
Variable Mean STD MIN MAX
Qnet -108 38 -226 -32
Qsw 4 11 0 76
Qlw -103 22 -165 -79
Qsen -0 10 -32 29
Qlat -9 13 -59 17

Despite the relatively strong wind speeds, the air-sea temperature difference is only 0.3°C so that the mean sensible heat flux Qsen is essentially zero. The latent heat flux Qlat is also small due to the low air temperature and high relative humidity. As austral winter proceeds, the incident shortwave radiation gets smaller, such that for this period the mean Qsw is also essentially zero. Thus, the net heat flux Qnet is due primarily to the net longwave flux Qlw. For this six day period, 95% of the net heat loss was due to the longwave loss.

While these estimates of the heat flux components include significant measurement uncertainty, the basic picture of persistent surface cooling over the shelf driven by net longwave radiation loss seems robust. During the pre-ice fall, insolation essentially vanishes and the diminishing difference between air and ocean surface temperatures makes the sensible and latent heat loss relatively small. Despite the high relative humidity, the sky re-radiates little outgoing longwave radiation back into the ocean, causing the dominant heat flux to be longwave radiation. To put a steady loss of 100 W/m2 into perspective, a 50-m deep surface mixed layer would cool about 0.25°C over a 5-day period. Thus, it would only take ~ 20 days for the surface mixed layer to lose ~ 1.0°C.

Chris Ribic and Eric Chapman surveyed birds on May 5th during daylight hours for 3 hours and 41minutes. Visibility was excellent and they made the following observations during transects between stations 24, 25 and 26. They also conducted 30 minute night surveys at 4:45, 19:00, 20:30 and 22:00. Here's a list species and numbers of birds recorded today:
Species Day Night
Antarctic Petrel (Thalassoica antarctica) 4 4
Cape Petrel (Daption capense) 10 3
Southern Fulmar (Fulmarus glacialoides) 12 0
Blue Petrel (Halobaena caerulea) 3 5
Southern Giant Petrel (Macronectes giganteus) 1 0
Snow Petrel (Pagrodoma nivea) 0 4
Unidentified 0 0

On 6 May, they surveyed for 4 hr 27 min. They did not record Blue or Antarctic Petrels and saw just two Cape and Snow Petrels. As we entered Marguerite Bay, they saw groups of Blue Eyed Shags and Kelp Gulls. Night surveys were conducted in the evening and will be reported in the 7 May daily summary. The following table summarizes the 6 May observations:
Species Number  (Day) 4:27
Antarctic Petrel (Thalassoica antarctica) 0
Cape Petrel (Daption capense) 2
Southern Fulmar (Fulmarus glacialoides) 27
Blue Petrel (Halobaena caerulea)
Southern Giant Petrel (Macronectes giganteus) 10
Snow Petrel (Pagrodoma nivea) 2
Kelp Gull (Larus dominicanus) 50
Blue Eyed Shag (Phalacrocorax atriceps) 38

Catherine Berchok reported that on May 4th, a Difar sonobuoy was deployed at station 20 which is close in proximity to the s5 mooring. Nothing but the ship was heard for 1.5 hours. Another Difar was deployed 5 miles from station 22. For 4.5 hours nothing was heard, but the ship.

On May 05, on the way to station 26, a Difar Sonabuoy was deployed in the presence of a minke whale spotted by Ari Friedlander. Some possible minke sounds were recorded about 5 minutes into recording. It is also quite possible, however, it was just humpback grunts because about 20 minutes later she started to record strong humpback calls just as Ari spoted them. The calls started off very plain, but soon they were varying like little snippets of song. Since we are moving fast, the signal was lost after 40 minutes.

She also deployed a Difar Sonabuoy about 5 miles before station 26. Some humpbacks were heard there as well. The signal was lost after about 40 mintues

On May 06, A Difar was deployed just after MOCNESS at station 28. Only a couple of possible humpback grunts were heard. This recording lasted a little over an hour. Another Difar was deployed about 4 miles before station 29. This time very nice loud humpback "chatter" was heard and the recording lasted 2 hours.

Another Difar was deployed on the way to rendezvous with the R/V Gould, in the presence of a little humpback that was flipper slapping and breaching. After two hours we had moved out of range of this buoy.

The final Difar was thrown in right after leaving station 30. There were no strong signals, but weak humpback calls were detected. At some point, as we turned back around to go back to the R/V Gould for the second time, signal to this last buoy was lost, but we re-entered the range of the previous buoy. Very loud humpback calls (song snippets again) were recorded. The total recording time between the two buoys lasted 4 hours, and was terminated when the previous buoy scuttled itself 8 hours after it was deployed.

It is important to remember that the whale calls are often overridden by ship noise and when the Palmer approached the Gould, Catherine thought of the noise from both ships as a duet with a couple of brief soprano parts made by the inflatable zodiac as it powered between the two ships to make the rendezvous.

Listening to whales and actually seeing them are two different things. Ari Friedlander reports that on there were no whale observations made during daylight hours on 4 may due to poor visibility and limited transit time. On 5 May, whale that observations began in the morning at 0855 local time in transit to station #25. Conditions were good; partly cloudy skies, and moderate seas/wind behind us. No whales were seen en route to station #25, and watch was suspended at 1007 local time. Observations resumed at 13:05 local time for the transit to station #26. Sighting conditions were similar to before. At 14:19, one minke whale was seen approximately 1 nm from the ship. At 14:43, two humpback whales were sighted at a similar distance to the ship. None of the animals showed any reaction to the passing vessel. As described by Catherine Berchock, a Sonobuoy was deployed after the minke sighting and humpback whale sounds were heard for approximately 30 minutes before acoustic contact was lost. Observations ceased at station #26, at 1545 local time. All it takes is sunlight, and some visibility and we'll see whales.

On May 6th, whale observations were not made during morning hours due to poor visibility. Before reaching station #29, however, conditions improved as we entered Marguerite Bay and at 17:43 a single humpback whale was sighted. As light was fading after the station, when the ship was maneuvering to rendezvous with the L.M. Gould, another humpback whale was sighted. This occurred at 2000, just after seeing 47 fur seals porpoising in front of and along with the ship. The humpback whale was socially active about 200 meters from the ship. The whale breeched once and was seen at the surface 'pec slapping' as the ship passed. As described above, Sonobuoys were deployed at both sightings and acoustic recordings were made at each site.

BIOMAPER-II/MOCNESS report (P. Wiebe, C. Ashjian, S. Gallager and C. Davis):
BIOMAPER-II has continued to be plagued by electronic problems. We were able to complete towyo's along the transect lines between Stations 20 and 22 (Station 21 was skipped) on May 4. While on deck during Station 22 because BIOMAPER-II cannot be in the water during a MOCNESS tow, we took the opportunity to clean and grease all of the cables and connectors, some of which had been causing minor ground faults. We had just put the towed body back into the water about 1700 when it was clear that the VPR had a serious problem - again connector related. One of the cameras was flickering and producing unusable images. BIOMAPER-II was recovered and taken apart on the deck, and within a few minutes, a bad splice in one of the VPR cables was isolated as the problem. This was fixed and about two hours later it was redeployed and the towyo to Station 23 was successful. Early on May 5th, during the run to Station 24, a different problem surfaced, three of the transducers in the echosounding system stop transmitting (one each of the 43 kHz, 200 kHz, 1 MHz). A decision was made to try to finish the transect, but two hours later, the other seven transducers stopped transmitting and power to the echosounder was turned off, but the towyo continued to collect VPR and Environmental data. BIOMAPER-II was recovered a couple of hours later at Station 24.

Trouble shooting the echosounder took place for the remainder of the 5th of May and throughout the 6th. A series of phone calls to the electronics engineers at HTI, the manufacturer of the echosounder, ensued and a comprehensive series of tests were conducted to try to isolate the reason why the echosounder transmitters no longer were functioning. Late on the afternoon of 6 May, with the echosounder largely disassembled, the problem was found. An integrated chip that controls the relays that transmit power to the transducers had shorted out and burnt up. Additional phone calls to HTI, resulted in a plan for trying to repair the disabled electronic board. This included getting the spare Multiplexor board from the R/V Gould, which had the key IC on it. Work through the night of 6 May resulted in a repair and initial tests indicate that the board is working again, albeit with one less relay than before. Testing of the components on the board and then more testing with the board back in the echosounder to make sure the transmit circuitry is actually working is now ongoing.

MOCNESS tows were taken on each of the last three days - at Station 22 on 4 May, at Station 25 on 5 May, and at Station 28 on 6 May. Several of these tows were hampered by the loss of flow meter counts when the reed switch on the flowmeter apparently failed at depth. Collections of zooplankton within Marguerite Bay appear to have lower concentrations than out in the middle of the shelf during the early part of the survey.

Cheers, Peter.