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

27 April 2002


Changeable weather is the hallmark of the Western Antarctic Continental Shelf and 27 April was no exception as the Palmer worked on outer portion of broad-scale survey line 7. The high winds of the day before had disappeared, but the large swell remained for most of the day. In the very early morning before sunrise, there was a clear spell and the full moon illuminated the scene. Throughout the morning, the winds were light (6 to 10 kts) out of the south, but a dense low fog developed cutting the visibility to short distances. Except for the swell, the surface of the sea had only light chop. By noon, the wind had shifted to the north northeast and was up to 15 to 20 kts where it remained until evening. The barometer rose slowly from 979 mlb in the early morning to 982 mlb around 1730. Air temperatures remained about the freezing mark (-0.5 to -1.0ºC).  About 2000, while work was ongoing at station 50, the wind and seas began to pickup.  By 2300, wind speeds were in the 30 kt range out of the northeast and sea conditions were rough enough that the deployment of BIOMAPER-II, while possible was delayed to wait for better working conditions.


April 27th was also the first of the Big Screen Movie nights on the Palmer, presented by Amy Kukulya and Romeo Lariviere.  The helicopter hanger was converted into a theater with a big white bed sheet screen on the helo-door during the day by an elite group of movie enthusiasts. At 2000 sharp, a DVD version of “Swordfish” played to an enthralled audience bolstered by galley gorp and popcorn.


Work at station 47 was finished in the early morning hours of 27 April with an APOP cast and work was completed work at 48, 49 and 50. Three CTDs and  a number of XBT casts were made. The XBTs were used to explore the extent of a deep warm water zone indicative on an intrusion of water from offshore.  A 1-m ring net tow was done at station 48; a MOCNESS and a 1-m Reeve net tow were done at station 50.  Seabird and marine mammal observations were made during daylight when the visibility was adequate. BIOMAPER-II was towyoed between stations 47 to 49 and was under repair for the transits between station 49 to 50.  Two sonobuoys were deployed along the trackline.


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

Today the CTD group did 3 CTD casts and 14 XBT casts (3 failures and 2 repeats) along the outer part of the 260 line. The XBT's, some launched April 28, but reported here for convenience, were done on the transit between stations 50 and 51.


These casts are quite varied having different mixed layer depths and properties. While all three have visible temperature and salinity variability in the pycnocline, Station 48 had the most energetic temperature structure seen so far on the cruise with layer thicknesses that range from 50 to 3 m. The deep warm temperature indicates some exchange with the Antarctic Circumpolar Current (ACC), which is not surprising for this station near the shelf break. Station 49 is rather like the other mid-shelf stations on this cruise with no deep warm water.  Finally, Station 50 in the middle of the shelf has clear indication of an oceanic water intrusion about 100 m thick.


XBT casts were made at Station 50 after the net tow (about 3 nm north of the station) and then every 5 km along the course to Station 50. The two closest XBTs indicated water warmer than 1.6ºC, but the remainder had no indication of Circumpolar Deep Water. It seems that the warm water was not coming from along shelf where the earlier intrusion was detected.


Station 48 (cast 52, 427 m). There was a uniform mixed layer to 70 m (-0.7ºC, 33.8) with chlorophyll measuring 0.6 μg/l.  A clear Winter Water (WW) layer was centered on 85 m.  The temperature profile was very ragged having 3 step changes (0.4ºC) in temperature over about 10 m separating 30 to 50 m thick layers. Smaller-scale structure was layers 5-10 m thick and energetic smaller-scale variability. There was a deep temperature maximum (1.6ºC) below 300 m.


Station 49 (cast 53, 484 m). The mixed layer was uniform to 70 m (-1.2ºC, 33.6) with chlorophyll measuring 0.3 μg/l.  A WW layer was centered on 90 m. There was energetic small-scale structure from 100 to 300 m, with a thickness of about 5 m.  There was a deep temperature maximum (1.4ºC) at 300 m.


Station 50 (cast 54, 392 m). The mixed layer extended to 50 m with uniform properties (-1.1ºC, 33.6, 0.35 μg/l.)  A WW layer was centered on 60 m. Energetic small-scale structure occurred from 80 to 250 m, with a thicknesses of about 5 m.  There was a deep temperature maximum (1.7ºC) at 230 m.  Several thick (30 - 40 m) isothermal layers were evident below 220 m.


Nutrients Status Report (Rob Masserini)

Yulia Serebrennikova and I have been kept out of trouble, mainly due to the CTD marathon inside of Marguerite Bay.  Since the last nutrient update, 489 samples from 26 stations and all of the associated calibrants and quality control samples have been run.  This equates to a sum of 2445 seawater sample analyses for nitrate, nitrite, ammonia, silicic acid, and ortho-phosphate.  These stations included the first samples from inside of Marguerite Bay for this cruise and represent approximately half of the nutrient samples that will be taken from this region.  The hydrography on the shelf is essentially the same as for transects 1 through 4 (please see last week’s report for the particular concentration descriptions).  The subsurface nitrite max between 75 and 100 meters approximately 40 to 60 nautical miles from the furthest offshore station persists in the cross section plots for transect 5 and 6.  There was a enrichment of nutrients right at the surface at stations 27 and 28 approximately 80 to 100 nautical miles inshore from station 23 for nitrate, nitrite, silicic acid and phosphate.  This appears to be associated with at local surface temperature maximum.  Within Marguerite Bay there is a depletion of nutrients within the mixed layer for nitrate, nitrite, silicic acid, and orthophosphate.  Average shelf concentrations of nitrate, nitrite, and orthophosphate within the euphotic zone are approximately 22.5, 0.2, 1.6 micromolar, respectively.  Surface concentrations of silicic acid displays more horizontal variability increasing from about 50 micromolar at the furthest offshore stations going through a maximum of slightly more than 70 micromolar approximately 90 nautical miles from the furthest offshore station and then decreasing within Marguerite Bay to 60 micromolar.  Nitrate, nitrite, and phosphate also decrease within the euphotic zone of Marguerite bay to roughly 18, 0.15, and 1.4 micromolar, respectively.  The big story from the nutrient lab is that although ammonia within the mixed layer does increase inside of Marguerite bay to approximately 2.2 micromolar, this is significantly different than the 4 micromolar concentration seen on the GLOBEC I cruise last fall.  These values are more comparable to the concentration seen on GLOBEC II winter cruise for this region.


Marine Mammal report (Debra Glasgow)

April 27 was a difficult day for observations of marine mammals as thick fog persisted throughout the day. Visibility in the morning was worse at <300 meters and only an Incidental watch was kept from 0904 to lunchtime at 1130.  Conditions improved somewhat in the afternoon, but visibility remained variable between <300 meters to <3 nautical miles. An On Effort watch was kept for most of the afternoon, however. Twelve fur seals and 1 unidentified seal were recorded. At the end of the day at 1659 as the light was fading, 4 humpback whales appeared out of the fog ahead of the ship at 118 about 0.1 n miles away. They ignored the ship, passing to starboard within 100 meters, and continued socializing, turning on their backs and waving pectoral fins, spyhopping, turning side on to each other and occasionally vocalizing above the water as they breathed. Some video footage was taken of this interaction though conditions were poor with heavy fog and a confused, beam on swell. On the tape is a clear ID shot of one of their flukes and an obscured shot of another. They disappeared back into the fog moments after the video was taken, still interacting with each other.


Sea Birds (Erik Chapman and Matthew Becker)


The seabird survey effort started on 27 April with a 1-m ring net tow at station 48 before the sun rose.  This station was just over the continental shelf near the shelf break and lots of phytoplankton was present, but no zooplankton visible to the naked eye.  A fog settled in overnight and limited our visibility during transit between stations 48 and 50.  Most of the day, visibility was about 200 m or less from the ship, too short a distance to collect data within the transect.  We did manage to collect data when the fog lifted for 30 min before we reached station 49 and for a little over 4 hours on our way to station 50 before darkness fell.  There were few birds observed during the survey, mainly open water species including Blue Petrels, Southern Fulmars, Cape Petrels, and Antarctic Petrels.  The low abundance of birds in the mid-shelf region has been consistent throughout the grid to this point.  Tomorrow, we'll be back in the ice in Marguerite Bay where we should see a shift in species assemblage to species typically found in ice like Snow Petrels and perhaps Adélie penguins.


A summary of the species and number of individuals of birds and seals observed during 4 hours, 10 minutes of daytime surveys between consecutive stations 48 to 50 is the following:


Species (common name)

Species (scientific name)

Number observed

Cape Petrel (“Pintado Petrel”)

Daption capense


Southern Fulmar

Fulmarus glacialoides


Antarctic Petrel                            

Thalassoica antarctica


Wilsons Storm Petrel

Oceanites oceanicus                     


Blue Petrel

Halobaena caeulea


Southern Giant Petrel                

Macronectes gfiganteus


Grey-headed Albatross              

Diomedea chrysostoma                     


Antarctic Fur Seal

Arctocephalus gazella




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

On April 27, at station 47 (67 14.712ºS; 74 31.74ºW), an APOP cast was made using juvenile krill (E. superba) with mean length and standard deviation of 35 and 5 mm, respectively. All animals were alive after the APOP cast even though a few animals were not as healthy as others before the cast. The experimental chamber was lowered and raised at a speed of 10 m/minutes and stopped at every 20 meters for a few minutes of data acquisition. The cast lasted about 1 and a half hour and did not seem to have much impact on the krill survival. The measured sound speed contrasts varied basically between 1.01 and 1.03 with no clear depth dependence.  No obvious difference in the measured sound speed contrasts between the down cast and up cast was observed.  The mean and standard deviation of the sound speed contrast for both the down and casts were 1.020 and 0.007, respectively. The density measurement was conducted on the same animals following the APOP cast. The measured density contrast was 1.027. The measured mean values of sound speed contrast is between those for the adults (mean length of 52 mm) and the smaller or younger juveniles (mean length of 27 mm) obtained from the previous casts (see daily reports of April 17 and 19 of this cruise), suggesting the mean values of density contrast did not show clear and consistent dependence on life stages despite the fact that the density contrast of the youngest juveniles did have the smallest value (see daily report April 19th).


In the evening at station 50 (67 50.807ºS, 72 25.978ºW), a Reeve net tow was made. Although not many krill were caught as hoped (only a few juveniles), more than 100  1.5-cm long live amphipods (Parathemisto), thousands of 2-3 mm long copepods (Calanus), and a few adult mysids (Arctomysis) were caught.  We are planning to make material properties measurements on Parathemisto and Calanus in the next few days.


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

Our thirteenth MOCNESS tow was conducted mid-shelf along transect line 7 at station 50 in ~ 400 m of water.  The tow was conducted to 360 m.  The tow was successful except that the strobe was not firing when the net was recovered. Krill furcilia were observed in many nets at this station, over the depth range of 250-75 m.  Larger krill were observed from 360-150 m and then again from 75-100 m.  Copepods were observed at all depths (0-360 m).  Ostracods were seen in the deepest net (360-250 m). Amphipods were seen from 75-50 m and then again in the surface net (25-0 m).  Diatoms were abundant in the 25-50 m interval.


BIOMAPER-II was deployed after the completion of deep water station 47 in the wee hours on 27 April and towyoed to station 48 on the edge of the continental shelf. and then onto station 49.   It was sidelined for the transit between stations 49 to 51 while repair work on the echosounder was performed.  Since the large swell caused the damage to the towing cable that forced a re-termination at station 29, the echosounder has had a problem with intermittent introduction of noise on the lower 3 frequencies.  At first, it was thought that the noise source might be associated with the ship operating in shallow water, but then it appeared while working in deeper water.  The noise source, which might be the result of a component failure in the echosounder, has proved to be difficult to track down.  After several days of trouble shooting, we do not seem closer to finding the source of noise problem, although several other problems have been identified and fixed.  The data on some frequencies is not of high quality, but the spatial patterns are still evident even with the presence of the unwanted noise.  An additional problem developed on 27 April.  The up-looking 120 kHz transducer abruptly stopped pinging during the transit between station 48 and 49, and then after some time again began to work, although intermittently. Peter Martin has had his hands full trying to keep the acoustic system functioning in BIOMAPER-II.


Volume backscattering in the offshore waters between stations 47 and 48 was very light throughout the water column, except near the surface on the 1 MHz echograms, which continued to show high backscattering where the VPR showed lots of diatoms and radiolarians in the water column.  There was also not much backscattering near the surface, except for some thin layers as the Palmer steamed from station 48 to 49. Along this transit, the bottom shoaled to around 390 m and there was a bottom scattering layer extending up above the bottom about 60 m.  There was a mid-water layer just above it, which was also about 60 m thick.  This mid-water layer showed up on the 43 echogram in spite of the noise, but not the bottom layer.  There was a second mid-water layer higher up in the water column (200 m below the surface) that was much patchier. There were occasional small krill-like patches in the upper mid-depth scattering layer. High backscattering continued to occur on the 1 MHz echograms in the diatom rich near the surface waters.


Cheers, Peter