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

21 April 2002

 

The fair skies of 20 April gave way to a fast moving, but turbulent storm that significantly reduced the scientific program on 21 April.  A falling barometer and increasing winds were accompanied by snow and fog.  By 0400, winds were in the 40 to 50 kt range and seas had built accordingly.  The stern decks were awash and access to them was curtailed. These conditions continued through the morning and although the winds subsided remarkably quickly in the afternoon to the 10 to 15 kt range, the storm and its after effects caused all of the programmed station work to be dropped except for the CTDs.

 

Work on the survey grid was completed at stations 24, 25, 26 27 along the outer to mid-shelf region of survey line 5.  This survey line will take us into the northern part of Marguerite Bay.  The abbreviated work schedule included only four CTDs at the stations, because of the high winds and seas. BIOMAPER-II remained in the water during the worst of the storm, primarily because it was too rough to recover it.  At Station 27, the BIOMAPER-II towing wire was damaged again, this time while on station with the fish parked at 40 m depth.  The towed body was retrieved at this station so that re-termination could commence.  Late in the afternoon, once the snow fall ceased and the fog thinned, some along track observations were made by the seabird surveyors, but conditions were not suitable for marine mammal observations.

 

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

The CTD group did four casts at four stations from the shelf break to the southern tip of Adelaide Island.  All four stations had high surface chlorophyll, energetic layering in the pycnocline, and a deep temperature maximum ranging from 1.3 to 1.5ēC. The surface layer structure, being two-layered at station 24 and homogenized at station 27, reflects the time history of winds over the last two days. The previous day's weak winds allowed a thin surface layer to develop while yesterday's strong winds effectively homogenized the mixed layer down to the Winter Water (WW) layer. Station 24 (cast 28, 443 m) had a two layer mixed layer with a cold (20 m) layer over a warm (50 m) one.  The surface chlorophyll is 0.8 μg/l.  A WW layer (-1.1ēC) exists below 70 m.  Energetic layering was occurring in the pycnocline.  There was no temperature maximum, but the bottom temperature was 1.5ēC.

 

Station 25 (cast 29, 408 m) had a uniform mixed layer to 50 m. There was a weak WW layer (-0.8ēC). The surface chlorophyll was 0.4 μg/l.  A weak temperature maximum (1.4ēC) occurred at 300 m.  There was some evidence of energetic layering in the pycnocline.

 

Station 26 (cast 30, 461 m) had a uniform mixed layer to 60 m, almost to the WW layer.  Surface chlorophyll was 0.5 μg/l.  The temperature maximum (1.3ēC) was at 350 m.  Layering was seen in the pycnocline.

 

Station 27 (cast 31, 761 m) had a uniform mixed layer to 50 m. There was no WW layer.  Surface chlorophyll was 0.5 μg/l.  Some energetic layering was seen in the pycnocline.  The temperature maximum (1.4ēC) was at 350 m.

 

Marine Mammal report (Debra Glasgow)

There were no cetacean observations on 21 April due to inclement weather. The day dawned with 35-45 knots, a Beaufort sea state of 7-8+, snow, and fog.  Although the wind dropped a little in the last hour or so of daylight, sea state remained high and visibility stayed around 300 meters or less.

 

Sea Birds (Erik Chapman and Matthew Becker)

High winds and low visibility due to snow prevented seabird surveying for most of the 21 April.  The winds died and visibility increased to just over 300 m at around 1430, and we were able to survey for two hours between stations 26 and 27.  We saw mostly birds following the ship, and again, Cape Petrel was the most abundant species.  Four Blue Petrels were sighted after not seeing one since the first transect line.  Two Antarctic Petrels were also seen.  This is another bird not seen for several days.  Densities appeared to be low as it usually is over the mid-shelf region .

 

A surface tow was completed at station 27 and the collection contained diatoms, copepods, a ctenophore and larval krill.  For the first time, no amphipods were evident in the sample.  Overall, the biomass appeared to be less than in previous tows.

 

An attempt to do night vision surveys will begin this evening because of the limited daylight survey period during the day.

 

A summary of the daytime survey results is the following:

 

Species (common name)

Species (scientific name)

Number observed

Cape Petrel (“Pintado Petrel”)

Daption capense

20

Southern Fulmar

Fulmarus glacialoides

8

Antarctic Petrel                            

Thalassoica antarctica

2

Blue Petrel

Halobaena caerulea 

4

Antarctic Fur Seal                        

Arctocephalus gazella      

9

 

 

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

The MOCNESS tow that was scheduled for the mid-shelf station 26 was scrubbed because of the high seas.

 

During 21 April, BIOMAPER-II was towyod between stations 24 to 27, in spite of the stormy weather.  Since, it was impossible to recover the towed body or even to bring it as close to the surface as normally done , we parked it a around 40 m while the CTD at each station was being completed.  This has worked effectively since the start of the cruise, but during the afternoon CTD cast at station 27, large swells coming in from the northeast were periodically dipping the stern down and then up fairly violently.  On one of the excursions, the towing cable jumped around the guard on the over boarding sheave that was intended to prevent such an event and got wedged into a bad spot. With the next surge, the cable was forced up and down in the wedge and the outer armor was stretched and warped, but no strands were broken.  Although the wire was freed minutes later, the damage was severe enough to warrant recovering the towed body to the deck and re-terminating the wire.  This work started around 2200 and continued until early morning on the 22 April.

 

The acoustic backscattering from plankton and nekton in the water column remain moderate in intensity for the most the transits between stations.  On several occasions, fairly strong backscattering layers would appear between 140 and ~200 m, resembling the krill-like patches that we saw on the first cruise last year in this region.  In mid-morning between stations 25 and 26, a very discrete layer developed that extended from the bottom about 120 m into the water column. It was most evident on the 120 kHz echogram and was not present on the 43 echogram, indicating that the scatterers were relatively small individuals.  Generally throughout the day, the near surface and near bottom layers were more intense than the levels generally seen yesterday and at the start of the towyos on this survey line.

 

Cheers, Peter