Report of Activities on the RVIB N.B. Palmer Cruise 02-02

5 May 2002

The N.B. Palmer was working the inshore sections of survey lines 9 and 10 on 5 May just off shore of Lazarev Bay and very close to the Bongrain Ice Piedmont on Alexander Island. (The Piedmont is 27 miles long and 12 miles wide and was first seen by Charcot from the Pourquoi Pas Island around 1908. It was named for Maurice Bongrain, surveyor and First Officer of the ship, who was responsible for the first map of the area.) Early in the morning, the sky was overcast with the clouds low enough to again hide most of the mountains of Alexander and Rothschild Island. The pack ice along the track line was composed of open leads with old floes, brash ice, and new ice. There were many big and small icebergs about and the curves in the ship's track reflected the need to maneuver around them. There was a pastel color to the sky and clouds where the sun came up close to 1000. The clouds cleared overhead towards the end of the day allowing for a lovely sunset, which took place strikingly behind a cloud layer as a filter and a very large iceberg in front. The clouds were luminous with the last rays of the day backlighting them.

The weather continued to hold and working conditions were very good. Wind speeds ranged from 4 to 10 in the predawn period to 15 to 20 kts during the day. The Palmer was far enough into the pack ice so that any swell motion was damped out. The barometer did a slow decline from 998.6 mlb just after midnight to a low of 990 mlb around 1700 before beginning to climb again. Air temperature varied between -4.5 and -9.6ºC. Sea surface temperature was at the freezing mark (-1.788ºC) and new sea ice was forming rapidly given the cold air temperatures and relative calm. Salinity was 33.204 psu.

The tedium of the seemingly endless sequence of station work and steaming was broken by a celebration of Cinco de Mayo in the late evening of 5 May. A pinata filled with goodies was created by Gaelin Rosenwaks with help from others, and music and plenty of Mexican food was on hand. The pinata was finished off at midnight with hefty wacks by Romeo Lariviere and Amy Kukulya, followed by a mad scamble to get the rewards. The planning committee led by Ana Sirovic did a great job, as did Theresa Wisner who made all the special Mexican treats.

Work was completed at broad-scale survey stations 75, 76, and 77 including 3 CTDs, a MOCNESS tow, an attempted ROV under ice survey, and an ice collection at station 76, and a 1-m ring net tow and an APOP cast at station 77. BIOMAPER-II was in for transits between the all of the stations. Seabird and marine mammal surveys took place during the daylight period and a sonobuoy was deployed during the transit to between stations 76 and 77.

CTD Group report (John Klinck, Tim Boyer, Chris Mackay, Julian Ashford, Andres Sepulveda, Kristin Cobb)

The CTD group did three shallow casts on 5 May at stations near the north coast of Alexander Island. All three stations had freezing mixed layers (about 40 m thick) with low chlorophyll. There was almost no density jump at base of the mixed layer, but rather temperature and salinity gradually increased to the top of the pycnocline which tended to be 100 to 150 m deep. These stations seem to be in transition to winter conditions of deep mixed layers (to 120 m) with freezing conditions. Surface salinity was lower than observed later in winter because surface freezing has only recently begun.

Station 75 (cast 78, 165 m). This short cast had a freezing mixed layer to 35 m (1.8ºC, 33.25 psu, 0.05 ug/l chlorophyll). A transition region (pycnocline-like) extended from 40 to 130 m and below was a slowly varying layer (0.0ºC, 34.3 psu).

Station 76 (cast 79, 189 m). Surface conditions (-1.8ºC, 33.2, 0.05 ug/l) were typical of other recent stations. Surface conditions were uniform over about 40 m, but merged continuously with a region of slowly increasing temperature and salinity. There was a slight density jump at 90 m, but slowly increasing conditions continued to 140 m where there was a stronger density jump. Deeper temperature and salinity continued to increase at about the same rate as the rest of the cast.

Station 77 (cast 80, 220 m). There were uniform surface conditions to 80 m (-1.8ºC, 33.3 psu, 0.05 ug/l chlorophyll). A deeper layer of gradually increasing temperature and salinity extended to 170 m, where there was a density jump signaling the top of the pycnocline. The deep tempertature and salinity increased gradually to the bottom.

Marine Mammal report (Debra Glasgow)

May 5 began and ended in pack ice. Mostly open pack, 7-8/10, large first year ice floes, many pools and cracks covered in nilas and some brash ice occurred for most of the day, thinner ice floes became more common later in the day with more brash, less nilas, and smaller pools, 9/10. There were many small icebergs within the pack ice.

The day was overcast, but with good visibility, the clouds clearing towards the end of the day presenting a beautiful sunset, which briefly outlined the ice in pink. Very little wildlife was seen, apart from a few snow petrels. At 1608, we started seeing crabeater seals from 69 06.78ºS; 72 59.58ºW. Three were swimming in the water between floes and two were on ice floes in the distance. Failing light ended survey at 1631.

Sea Birds (Erik Chapman and Matthew Becker)

Surveys were conducted as the ship traveled between stations 76 and 77 through 8 to 10/10ths ice coverage, at least 20 nautical miles from the ice edge. Approximately 80% of the ice was one year old floes, 5 to 10 m in diameter. The remaining 10% of the ice was alternately nilas, new gray, and brash ice. BIOMAPER-II found very little biomass in the water column in this area. A surface tow at station 77 indicated no diatoms and very little zooplankton, including larval krill, amphipods and copepods, at the surface.

Bird sightings reflected ice conditions and the biology of the water column. Few birds were seen overall, despite ice conditions preferred by Snow Petrels and Adélie Penguins. These species were observed, but in very low numbers. This is interesting because this is the same area where large numbers of Snow Petrels were observed during the fall cruise last year. At that time, there was a well-defined cold, coastal current in the area and virtually no ice. The area is now well within the pack ice and, according to physical oceanographers, the coastal current is not a well-defined feature during this cruise. It will be interesting to see whether Snow Petrel abundance increases as we move toward the ice edge during tomorrow's survey.

Adélie Penguins continue to be observed in low abundance during surveys, despite the presence of their preferred ice habitat. To this point, it appears that the survey has not included an area with the right combination of ice and prey that would create an ideal habitat scenario for Adélie Penguins. Where these conditions might occur in the vicinity of Marguerite Bay remains a mystery, one that we hope to investigate when we complete the grid.

A summary of the species and number of individuals of birds and seals within the 300 m transect during 2 hours, 26 minutes of daytime surveys between consecutive stations 76 and 77 is the following:

Species (common name)	Species (scientific name)	Number observed
Snow Petrel	Pagodroma nivea	12
Adélie Penguin	Pygoscelis adeliae	1

Material Properties of Zooplankton Report (Dezang Chu, Peter Wiebe)

On May 5, measurements were again made of material properties on E. superba. The APOP cast was conducted at station 77 (68 57.654ºS; 73 33.180ºW). These animals were caught either on April 23 or April 30 by Kendra Daly, with a mixed size distribution from 18 mm to 56 mm. The mean length of the animals was 28 and the standard deviation was 9 mm, larger than those from the previous casts,

With the help from Peter Martin, the problems of the APOP mentioned in the 4 May report were fixed. There were two problems. One was a loose contact between the transducer wires that were directly connected to the ceramic disk of one of the transmitters, resulting in trapped water inside the potting block. Another problem was bad continuity in one of the cable wires. The system was operational around 1930, just in time for the scheduled APOP cast.

The sound speed contrast from the shipboard measurement was 1.028, while the mean value of the sound speed contrast was from the APOP cast 1.024. The standard deviation was only 0.001, again, very small. There was basically no obvious difference between the down and up cast (both were 1.024). Because the bottom was only 180 m, the APOP cast was deployed to 165 m, instead of 205 m as previously done. The density contrast was 1.022. Both sound speed and density contrasts of this animal group with a wide range size distribution were in the ranges of what we obtained from the previous measurements for more uniformed size groups. No surprises.

Zooplankton (MOCNESS/BIOMAPER-II) report (Carin Ashjian, Peter Wiebe)

The nineteenth MOCNESS tow was conducted in early afternoon just off of Alexander Island at the eastern end of survey line 10. The site was covered in ice, which made controlling ship speed difficult. John Higdon did a great job driving during the tow. The bottom depth was quite shallow (150 m) and we were able to deploy the net only to 126 m in order to avoid letting out more wire than the bottom depth. Only 5 depth intervals of 25 m each were fished. Very little was found at this site; low abundances and diversity were the characteristics. In the net that fished the total water column (0-126), two ctenophores were caught and approximately 100 largish krill. This net must have intercepted a small krill patch. Although a few krill were caught in all subsequent nets, this first net was the only one that caught any abundance at all. Copepods were collected in the bottom net (100-126) and 1 was collected in the 0-25 m net. One fish was collected from 75-100 m along with two chaetognaths. A small amphipod was collected in each of the 50-75 m, 25-50 m, and 0-25 m intervals. Krill and krill furcilia were collected at the surface. Despite the low catch, all net statistics from during the tow indicated that the net was fishing correctly; the net was at a satisfactory angle throughout the tow and reached the surface in the proper orientation with no nets “hung up” partially closed. The strobe was functioning only intermittently at recovery. The net response did not function throughout the tow.

BIOMAPER-II was towyoed along the tracklines between stations 74, 75, 76, and 77 during 5 May. The bathymetry along the tracklines was high variable and consisted of shallow peaks 100 to 200 m below the surface and deep narrow canyons, some extending to a 1000 m. The backscattering also varied significantly. The strong krill-like layers seen after leaving 74 headed for station 75 gave way to much lighter volume backscattering that was strongest near the bottom and decreased near the sea surface. Similar levels of backscattering were present on the line between stations 75 and 76, which last year at this time had very strong scattering krill-like layers at mid-water depths (50 to 120 m). As noted above, the MOCNESS tow caught a low catch at station 76 and BIOMAPER-II deployed immediately after the tow and also indicated that this site was one low plankton abundance both with the acoustics (all frequencies) and the VPR. During the transit to station 77, the situation changed. Mid-way to the station, dense krill-like layers were encountered in the late afternoon about the time a number of crabeater seals were sighted. The layers and patches formed from about 40 meters below the surface down as deep as 150 m with thicknesses of 90 m. On one occasion, there were vertical plumes extending up to near the surface. When BIOMAPER-II passed through the layers as it was being towyoed vertically, the VPR got images of krill confirming the fact that the acoustic backscattering was coming from these animals. The intense backscattering layers diminished substantially by the time station 77 was reached, although there was still some backscattering in the water column with a layer starting about 20 to 25 meters and going down.

From the acoustic and VPR data now collected along the three completed survey lines extending off of Alexander Island (lines 8-10), it appears that the krill hot spot in this area has changed some since last year. And it may have something to do with the fact that there is ice pack in the shoal areas along Alexander Island where there was none last year. Last years hot spot was close to land and this area is now fairly deep in the pack ice and has low backscattering levels. The krill-like layers and patches have moved further offshore and seem to be sitting closer to the vicinity where the ice edge starts. It will be interesting to see if this pattern holds on the last three survey lines further south on the grid.

Cheers, Peter