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

17 April 2002

 

On April 17th, work began in the early morning hours at deep ocean station 12 out at the end of survey line 2, where the water depth was 2941 meters. In the early morning light, the horizon was visible for the first time in days, although the skies were still heavily clouded. Winds were in the 25 kt range out of the east northeast (070) and the air temperature were around -2.2C. The barometer, at 978 mlb, was not changed much from last couple of days. Working conditions were relatively good. During the course of the day, the Palmer moved from the offshore location to mid-shelf station 14 on line 3 with a stop at the shelf break to work at station 13. By evening, winds were up in the high 20's to low 30's, but fortunately, the seas were our port quarter, so the ride was not bad. The skies remain cloudy and sometimes the cloud deck lowered almost to the sea surface. There was little in the way of precipitation. The work-of-the-day included 4 CTDs, an APOP cast at station 12, and a 1-m ring net tow at station14. BIOMAPER-II was towyoed between stations 12, 13, and 14 and along track sea bird and mammal observations were made during daylight. Three Sonobuoys were also deployed along the trackline.

 

Although the day started out routinely enough, there was an event that was not routine. About the time that the APOP cast was being completed (0940), preparations to deploy BIOMAPER-II were underway. When the doors to the van used to store BIOMAPER-II on deck were opened, an acrid black smoke came rolling out and it was evident that there had been a fire at the back of the van where the electrical panels were located. Quick action on the part of the MT Stian Alesandrini got the report of a fire to the bridge, which triggered off the ships fire alarm. All the scientists and technical support people rapidly grabbed survival suits and life vests, and went to third level lounge, which is our muster station in case of emergencies. There was a period of waiting while the crew and electronic technicians did an inspection to try and determine what caused the fire, which was out at the time of discovery. The consensus was that the fire started with the failure a Makita battery charger, which was at the back of the van close to one of the electrical panels. The fire produced a thick black soot, which covered all surfaces, and the heat ruined some of the electrical wiring, but the damage was relatively little. BIOMAPER-II was not damaged, so once the assessment was completed, work commenced towards getting the towed body into the water. Cleanup of the deck van and the re-wiring of the damaged circuits began shortly after. The ships engine room crew, led by Johnny Pierce, and the Raytheon technical support people did a great job in helping to get to van back into working condition. Members of the BIOMAPER-II group also worked very hard and put in long hours to right the situation.

 

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

The CTD group did five casts at four stations at the outer part on two lines during the later portion of the 16th of April and most of the 17th. The Antarctic Circumpolar Current (ACC) was apparent in the outermost stations on the line and was at the shelf break at the outer end of the 420 line (the second survey line), but not the 460 line (the third line). The mid-shelf station on the 420 line shows no influence of warm oceanic water.

 

Station 11 (Cast 13, 917 m) at the shelf edge had a mixed layer to about 40 m above a warm layer (30 m thick) and a cold layer (50 m thick). The temperature indicated extensive layering (10 to 20 m thick) down to 400 m, which was matched similar salinity structure. A cold layer occurred between 300 and 400 m. The temperature maximum (1.7C) occurred at 450 m. Below 750 m to the bottom was a colder layer with higher oxygen. The moderate temperatures imply that the ACC was not hugging the coast.

 

Station 12 (Cast 14 and 15, 3102 m) in deep water off the continental shelf, had a mixed layer to about 50 m over a cold layer (-1.0C) to about 80 m. Surface chlorophyll was above 0.6 ug/l. A 100 m cast was done to sample with the FRRF. No bottles were closed on this short cast. The deeper cast detected some temperature and salinity layering in the pycnocline above the temperature maximum (2.0C) and oxygen minimum at 200 m depth. This temperature confirms that the station is within the ACC. Temperature decreased continuously with depth as salinity remained nearly constant. Oxygen rose slightly.

 

Shelf edge station 13 (Cast 16, 774 m) had the familiar 3 layer structure with a uniform surface mixed layer to 35 m over a warm layer over a cold layer (30 m thick). Jagged temperature and salinity traces indicate small scale layering in the pycnocline. The temperature maximum (2.0C) was at 250 m indicating that the ACC was against the coast at this station. The water from 600 m to the bottom was about 0.3C colder than the water above.

 

Station 14 (Cast 17, 528 m) had a very uniform mixed layer to 50 m with a slight WW layer below. The main pycnocline had small vertical scale temperature and salinity variability down to the temperature maximum (1.3C) at 370 m. The water from 480 m to the bottom was slightly colder (0.1C) and higher in oxygen. This station is a typical coastal station.

 

Marine Mammal report (Debra Glasgow)

The marine mammal survey began at 1118 on 17 April as we started our transit to Station 13 and continued through to our arrival there at 1615. Visibility was variable with patchy fog, but was fairly good for most of the day though the sea state was Beaufort 6. One seal was sighted at 1452, many birds accompanied the ship throughout the day, and several icebergs were passed. At 1357, what looked like a large light blue body was sighted moving under the water bearing 110 degrees, 200 meters to port and swimming in direction 080 degrees (position -66 14.04S; 71 18.03W). The body did not surface or blow, so it could not be recorded as a definite whale sighting since it remained unconfirmed. However, earlier at 1335, Ana Sirovic had called to say a sonobuoy had been deployed and she was hearing blue whale sounds. Another directional sonobuoy was deployed after being informed the sighting and from the bearings received, the indications were that the whale sounds were coming from the NE, which is about where the sighting would have been at the time. So this was potentially, an unconfirmed blue whale sighting. A careful watch was kept by several observers, but no whale surfaced within sight. Conditions were difficult with variable visibility and many whitecaps, however.

 

Sea Birds (Erik Chapman and Matthew Becker)

April 17 began with the taking of morphometric data from a Wilson's Storm-petrel that had landed on the ship. We then surveyed for 5 hours between stations 12 and 13 off the shelf break. Virtually the same species assemblage was seen as observed off the shelf break on the first transect line. The Cape Petrel was the most common species and the Southern Fulmar was also seen in good numbers. These species were mainly following the ship. We saw a few Wilsons Storm-petrels, Grey-headed Albatross, and Blue Petrels, and a single Antarctic Petrel.

 

A surface net tow at station 14 that contained a large amount of diatoms, larval krill and some amphipods was done in the evening. A summary of the results is the following:

 

Species (common name)

Species (scientific name)

Number observed

Cape Petrel (Pintado Petrel)

Daption capense

124

Southern Fulmar

Fulmarus glacialoides

64

Antarctic Petrel

Thalassoica antarctica

1

Blue Petrel

Halobaena caerulea

6

Unidentified Prion

 

1

Grey-headed Albatross

Diomedea chrysostoma

6

Wilsons Storm-petrel

Oceanites oceanicus

10

unidentified Skua

 

0

Southern Giant Petrel

Macronectes giganteus

3

Antarctic Fur Seal

Arctocephalus gazella

2

 

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

At station 12 (-66 2.286, -71 11.340), the station off the continental shelf, we did an APOP (Acoustic properties of Plankton) cast to as deep as 200 m, measuring variation of sound speed contrast of live krill as a function of depth. We believe that this is the first in situ measurement ever conducted on Antarctic krill (Euphausia superba). A dozen of live adult krill were placed in the acoustic chamber of the APOP. Measurements were conducted on deck of the ship and at 20 m depth intervals down to 200 meters, the limit of the conducting cable. All the krill were still alive when the APOP was brought back on the deck. The temperature was 0.5C at the surface and was minimum at about 70 m (-1.06C) and increased to 2.0C at 200 m. The measured sound speed contrasts of the krill from the down cast and up cast were consistent. The overall mean sound speed contrast was 1.0238 and the standard deviation is 0.0030. There seemed to be a weak correlation between the temperature or sound speed profile of the seawater and the sound speed contrast.

 

In addition to the in situ sound speed measurements, a density measurement was also conducted on the krill used in the sound speed measurement. The measured density contrast was 1.028640.0042, which is about 0.3% more than what we measured on a different group of krill reported earlier. Although the two measurements were conducted independently, they agreed with each other very well, indicating the dual-density method is providing consistent results.

 

Water Sampling for Microzooplankton (Phil Alatalo)

The objective of our microplankton study is to observe, record, and analyze motility patterns and size spectra of microplankton in the water column. We have conducted similar studies throughout the Georges Bank GLOBEC study area as well as on the two previous cruises here in the Southern Ocean. Characterizing the microplankton helps us corroborate water masses, assess size and distribution of this particular fraction of the plankton, and understand basic swimming patterns in microzooplankton, which have been shown to be important food items in other ecosystems.

 

The recording system itself consists of a black and white video camera outfitted with macro-lens, a microscope ring illuminator, and an SVHS recorder. Samples are gently siphoned from the CTD bottles in order not to damage fragile protozoans and phytoplankton. One sample is filmed, while a duplicate sample is preserved in Lugol's preservative for later identification and enumeration. We are particularly interested in sampling the surface waters, the bottom or deepest depth, and the pyncnocline.

 

To date, we have sampled all 13 stations. Video recordings will be analyzed back in Woods Hole for motility parameters and size spectra. Preserved samples will be placed in settling chambers for identification and enumeration. Cursury notes on each video recording reveal the following patterns:

 

Typically, surface waters have the most numerous microplankton. Diatoms, such as Corethron sp. and Ditylum sp. were the most common along the shelf stations. On leg 2, at the shelf break, Station 11, chain diatoms, such as Chaetoceras sp. and filamentous Rhizoselenia became dominant. Off shelf, at Station 12, only the surface water held lots of microplankton; below 100 m very few particles were present. Mesodinium, a small ciliate with a characteristic 'hopping' swimming motion was present at nearly every station at the surface. Most abundant in offshore surface samples, it was found in the 225 m midwater oceanic intrusion at Station 9, mid shelf, leg 2. Particles were extremely abundant at the innermost station 7; however, no large diatoms, ubiquitous to most areas, were present there.

 

Gaelin Rosenwaks, Amy Kukulya, and Philip Alatalo are responsible for microzooplankton sampling and recording and analysis supervised from afar by Scott Gallager, WHOI.

 

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

In spite of the hour delay in the deployment of BIOMAPER-II at station 12 as a result of the fire in the deck van described above, the system once deployed continued to run well. Acoustic, video, and environmental data were collected on the long transit between stations 12 and 13 and on the shorter run between stations 13 and 14, and 14 and 15. In the deep water of the Antarctic Circumpolar Current, groups of large targets were observable on all four lower frequencies (43, 120, 200, and 420 kHz) at mid depth levels, but there were few of the smaller targets. The water column looked pretty sparsely populated below the surface layer, except for the big targets. There was somewhat higher backscattering in the mixed layer. This pattern continued all the way to the station 13 at the continental shelf break. After coming onto the shelf, in the evening, moderate scattering was observed starting about 260 m below the surface and going down to the bottom (around 500 to 550 m). There was also a surface enhancement of scattering down to about 80 m with a more intense layer in the 40 to 65 m depth zone. Much lighter scattering was between 80 and 260 m.

 

 

Cheers, Peter