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

15 April 2002

 

The start of the survey work at the northern end of the SO GLOBEC grid continued to go well. Working conditions on 15 April remained reasonably good for most groups in the scientific party, although aspects of the weather have hampered the observational work of the bird and mammal surveyors. Work was completed at the remaining stations on line 1 (stations 4 to 6) and also at station 7, the inner most station on line 2. This included CTDs equipped with both the FRRF and the Microstructure systems at each of the four stations, a MOCNESS tow at Station 4, a 1-m Reeve net live animal tow at stations 4 and 7, and a 1-m ring net surface zooplankton tow at station 7. Four sonobuoys were deployed along the trackline to listen for marine mammal vocalizations and BIOMAPER-II was towyod along the tracklines between the four stations.

 

The weather on 15 April remained dark and dreary with thick clouds and a light fog and snow limiting visibility to between a few hundred meters to a mile or two. Snow flurries were common throughout the day and the decks were wet and icy. The wind was out of the northeast (040) at 15 to 20 kts and with the ships course headed towards Adelaide Island, we were traveling in the trough. But the ride was quite good. Water temperature (-1.473C) inshore was about a degree colder than offshore and the water was fresher (33.154 psu) by about half a part per thousand. The air temperature during the day was just below freezing (-0.6C). Barometric pressure was ~979 mlb.

 

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

The CTD group did four casts at four stations to complete the northernmost (500) line of the grid.

 

Station 4 (Cast 6, 348 m) had a surface layer to 50 m with increasing temperature and salinity across the layer. A 25 m thick Winter Water (WW) layer (-0.8C) was centered on 75 m depth. A weak temperature maximum (1.6C) occurred at 250 m. There was both thin (2 m) and thick (10 m) layering throughout the cast.

 

Station 5 (Cast 7, 684 m) had uniform surface layer to about 40 m. A thick pycnocline extended from 50 to 150 m with energetic salinity variations and a very ragged temperature profile with layers of varying thickness (about 1 to 10 m). There was a clear temperature maximum (1.5C) at 300 m.

 

Station 6 (Cast 8, 413 m) had a surface layer to about 75 m with a gradual, steppy salinity increase, but a ragged temperature profile. The pycnocline was characterized by two layers (20 m thick, warm over cold) with opposite changes of salinity. Considerable small scale structure occurred throughout the upper 2/3 of the cast. Bottom temperature was uniform (1.2C) with no indication of a temperature maximum.

 

Station 7 (Cast 9, 145 m) had continually increasing T and S throughout the cast with a bit of a change in slope at 35 m. A second slope change occurred at about 110 m. Small temperature and salinity reversals occurred throughout the cast.

 

Surface salinities are 33.4, 33.4, 33.25, 33.25, and 33.2 for stations 4, 5, 6, 7 and 8, respectively. This seems a weak, if any, indication of a coastal current. A salinity section plot, to be produced soon, should clarify any coastal current.

 

Surface chlorophyll is 0.2 to 0.3 mg/l (decreasing towards the coast) through the surface mixed layer on every cast, reducing to below detection levels by 100 m.

 

On the positive note, we have had no real problem with bottle valves or leaking. One leaking bottle was removed from the rosette. However, we are having consistent problems with bottles closing. One to four bottles on every cast do not close. A variety of fixes have not improved the situation. Attempted fixes continue.

 

Marine Mammal report (Debra Glasgow)

The 15th of April was another foggy day with visibility restricted to <1 nautical mile for most of the day, but this was somewhat variable. The horizon was not visible at any time. Nevertheless a mammal survey was kept for most of the daylight hours while in transit between stations. Several fur seals were sighted and a lot of foraging petrels accompanied the ship. Observations began at 0810 and ended at 1710.

 

At 0922 at 66.18.94S, 68.39.03W, a porpoising animal was observed with a smallish dark body (not seal like) creating a minke like bow wave (no dorsal fin was seen). It was heading away from the ship at a distance of 0.05 nm. In all, the animal was seen 3 times, but in poor visibility and foggy conditions and as it was moving very fast, it was difficult to identify. The ship passed several icebergs visible on radar, but most were not visible in the fog. We passed through an area of 2-3/10 brash ice and bergy bits between 66.26.61S, 68.14.12W and 66.28.68S, 68.06.53W.

 

Sea Birds (Erik Chapman and Matthew Becker)

On 15 April, sea birds were surveyed for 6 hours and 21 minutes between consecutive stations 4, 5 and 6 on the survey grid. Visibility was borderline, with snow and mist reducing our visibility to within 600 m of the ship at various times. The surveys were over the shelf, approaching stations near land. Most of the birds observed were again following the ship. Abundance and diversity was lower today, and a single species, the Antarctic Petrel, was by far the most abundant bird observed. Cape Petrels and Southern Fulmars were relatively uncommon compared with yesterday's surveys off the shelf, and Blue Petrel, prions, and Grey-headed Albatross were not seen at all today. However, we did see a single immature Kelp Gull, three unidentified Skuas and 2 Wilsons Storm Petrels. Antarctic Fur Seals were also observed again, though in smaller numbers than during yesterday's surveys. A second 1- m ring net surface tow was made at Station 7 and caught adult Euphausia superba, copepods, and larval krill in the top 100 m of the water column. Heavy snowfall this evening once again prevented us from doing night surveys. A summary of the observations is the following

 

Species (common name)

Species (scientific name)

Number observed

Antarctic Petrel

Thalassoica Antarctica

138

Cape Petrel (Pintado Petrel)

Daption capense

32

Southern Fulmar

Fulmarus glacialoides

21

unidentified large Skua

 

3

Southern Giant Petrel

Macronectes giganteus

3

Wilsons Storm-petrel

Oceanites oceanicus

2

Kelp Gull

Larus dominicanus

1

Antarctic Fur Seal

Arctocephalus gazella

8

 

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

The material properties of zooplankton (the sound speed contrast and density contrast of an individual relative to the surrounding seawater) are very important values that are needed to interpret acoustic backscattering data from zooplankton. However, few of these measurements have every been made on plankton and little is known about how they vary for any species with depth, season, or life stage. This project is focusing on obtaining such data for zooplankton, especially krill, in the SO GLOBEC study region. A 1-m diameter Reeve net is being used to collect zooplankton as gently as possible to insure that they are retrieved in living condition. The Reeve net was first used Station #4 on 15 April, but too few individuals were caught to use in the experimental apparatus dubbed APOP (Acoustic Properties Of Plankton). A second attempt to catch significant number of krill took place at station 7, where BIOMAPER-II spotted sizeable patches of krill (see report below). The first tow only caught a few krill. We then steamed back to where the krill patch was originally located. The second Reeve Net tow was quite successful and caught several hundred of krill, including adults and juvenile krill. Unfortunately, most krill were caught between the outside of the cod end bucket and the mesh bag that holds the bucket, but about 30 adults and more than 70 juvenile krill were in good condition. Shortly after the krill were brought up to the deck, shipboard measurement of the krill density contrast was conducted. The measurement was conducted with a newly developed system to accurately measure the density of small live animals known as the dual-density method. A motion compensated weighing method was used to provide an acceptable accuracy. It involves two digital electrical balances capable of exporting the measured readings at 5 Hz. One electrical balance functions as a reference reading with a calibration mass on its weighing platform and the other weighs the object of interest. The resultant relative accuracy of this motion compensated weighing method is better than 0.01%. The measured density of the adult krill (mean length of 50.9 mm and standard deviation of 2.7 mm), was 1.02576 0.0004. This density contrast is relative small compared with that of decapod shrimp (Palaemonetes vulgaris), whose density contrast is almost always greater than 1.04.

 

The acoustic unit of the APOP was having problems with its cable connectors. The male pigtails and female ping connectors were not well matched, giving rise to bad connections. This acoustic unit is used to measures the sound speed contrast. Peter Martin has been working to correct the electrical problems and hopefully it will be operational later on 16 April.

 

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

The second MOCNESS tow, and the first of the grid station work, was conducted at standard station #4 at mid-shelf in 350 m of water along the northernmost transect line. The tow went quite well, with the exception that the net response again failed to function. There was a very interesting and marked vertical gradation of taxa. The lower depths (350-150 m) contained primarily juvenile or adult krill of two species and copepods. Small salps were observed from 250-325 m. By contrast, a large salp of a different species was seen in the 100-150 m depth range. At 100 m, large krill disappeared and krill furcilia were observed only to 75 m. Diatoms and copepods were observed from 25-75 m. The upper 25 m contained amphipods and diatoms, with no krill and very few copepods. A very successful first survey tow.

 

Acoustic and Video Plankton Recorder surveying of the zooplankton and nekton along the survey trackline with BIOMAPER-II continued to go well. Few krill patches were observed at mid-water depths along the inner portion of the shelf along the transect line 1 and for the most part, the intensity of volume backscattering was moderate to light. The usual deep concentration of scatterers was present extending 60 meters or more above the bottom in water depths that varied from 350 m to more than 500 meters. There were also thin scattering layers near the surface which showed up better on 120 kHz frequency than 43 or 200 kHz and might have been related to rapid changes in temperature and salinity in the pcynocline. As we came into station 7, which was located very close to the Fuchs Ice Piedmont on Adelaide Island, we came across a very intense column of backscattering which went from the bottom at 250 m to about 50 m where it joined a rather strong horizontal layer centered at about 50 m. It looked like we had crossed some kind of front that was highlighted acoustically. Shortly after that, we entered an area of extremely high backscattering within 20 meters or so of the bottom that net tows demonstrated were composed of large adult and juvenile krill. The high backscattering extended up to about 60 m below the surface albeit somewhat reduced in intensity.

 

 

Cheers, Peter