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

20 April 2002

On April 20, the N.B. Palmer was at the offshore end of survey lines 4 and 5 in water depths of 3500 meters. These stations are about as far apart as any on the survey grid and they require a lot of steaming time to move from one to another and a lot of time to do a CTD profile from the surface to the sea floor or a MOCNESS tow to 1000 m. Thus, we worked at only stations 22 and 23 on this day.

The good weather continued, much to our amazement and pleasure. There was a beautiful sunrise with clear skies overhead. The only clouds were out on the horizon. In the early morning light, there were a number of icebergs off in the distance, one of which looked like a ship on the horizon with a bow, tall mast, and aft cabin. Bergy bits of ice were floating closer by. Once again, there was very little wind, around 10 kts out of the north northeast, and the seas were just choppy with a low underlying swell. The barometer remained fairly high at 998.7 mlb and the air temperature was holding steady at -0.6ºC. In early afternoon, the skies had lost their lovely blue and were again overcast. Wind remained low, but the barometric pressure had started to drop. Surface salinity (33.733 psu) out in this Antarctic

Circumpolar Current location was higher than on the shelf and sea surface temperature was -0.571ºC. By mid-afternoon, a fog approached the ship from the north ultimately reducing the visibility to less than a mile. The winds picked up in the evening and the barometer kept dropping, a portend for the approaching storm.

During 20 April, 3 CTDs (2 deep and one shallow), a 1-m ring net tow at station 22, and a deep MOCNESS tow at station 23 were successfully completed. Two sonobuoys were deployed along the transect lines. BIOMAPER-II towyos were made along the tracklines between each of the stations and while visibility remained good, seabird and mammal observations were also made.

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

The CTD group did 3 casts at two stations. Both stations were off the shelf with depths more than 3000 m. At station 22, a second cast was done with the FRRF to 100 m. The conditions at both stations were very similar and typical of conditions in the southern Antarctic Circumpolar Current. Mixed layers had uniform properties with rather high chlorophyll values. Winter Water was present at both stations below the mixed layer. The temperature maximum was above 1.9ºC and occurred at the bottom of the pycnocline. A deep salinity maximum (1000 m) indicated lower Circumpolar Deep Water.

Station 22 (casts 25, 26, 3332 m) had a uniform mixed layer to 65 m. Surface chlorophyll was above 0.8 μg/l. The temperature maximum (2.0ºC) occurred at 400 m. There was strong layering in pycnocline with layer thicknesses around 10 m.

Station 23 (cast 27, 3670 m) had a uniform mixed layer to 50 m. Surface chlorophyll was above 0.6 μg/l. The temperature maximum (1.9ºC) was at 300 m. Strong layering was again seen in pycnocline with thicknesses around 10 m.

Phytoplankton Primary Production (Wendy Kozlowski)

Primary production during the SO GLOBEC grid survey on NBP02-02 is being measured using two principle methods. First, net daily production is being estimated by carbon uptake during 24 hour simulated in situ (SIS) deck incubations. Water for these experiments is collected once per day from the CTD rosette, at the station most prior to sunrise, at depths of zero to thirty meters. Secondly, water column profiles are being generated using a Fast Repetition Rate Fluorometer (FRRF) as part of the CTD package, at all stations where the depth is less than 500 meters. Chlorophyll measurements and particulate carbon sampling are also being completed for estimation of phytoplankton biomass.

During the first week of sampling, the primary production group has completed seven SIS experiments, at stations 1, 4, 8, 11, 15, 18 and 22. Preliminary results through station 15 show levels approximately twice as high as those measured in this area during first SO GLOBEC survey cruise, a year ago. The FRRF has been deployed at fifteen stations, with two extra casts at deep stations, allowing us to sample some off-shelf locations. Chlorophyll samples have been taken at all twenty three stations, at twelve depths throughout the water column. Those same depths have been sampled for particulate carbon at twelve stations thus far. Unlike production, chlorophyll measurements (through station 14) show similar levels to those seen during the first survey cruise, with levels in the mixed layer ranging from about 0.4 μg chla /l to 1.4 μg chla /l with a maximum of 2.2 μg chla /l at station 14, and the phaeophytin to chlorophyll ratio remaining between 0.24 and 0.38 at these same depths. Generally, little to no chlorophyll is being seen in the deeper water samples, with the exception of stations 9, 10 and 14, where there was a slight increase at the bottom of the water column, and at station 11 where there was a distinct sub-mixed layer maximum in the 700 m sample, corresponding to a fluorescence increase and temperature decrease seen in the CTD profile.

Marine Mammal report (Debra Glasgow)

April 20 dawned fine and calm with a Beaufort sea state 2, which rose to 3 later in the day. Visibility was excellent early in the day. It was the first blue sky of the voyage with 3/8 cloud cover and a colorful sunrise at 0836. The marine mammal survey started at 0821 for the 27.3 nm transit to Station 23 and ended in fog with poor visibility at 1320 as we arrived on station 23. There were 2 whale sightings for the day both like humpbacks. The first was a group of 2 whales sighted by Ana Sirovic at 1148 and the other was of 4-5 whales sighted by John Higdon at approximately 1529 while we were on station in the fog. Only one fur seal was seen today. There were several icebergs visible throughout the morning and a few growlers and small bergy bits. The cumulative total of cetacean sightings of one or more individuals for the voyage to date is 18, and the total number of whales is 41.

Sea Birds (Erik Chapman and Matthew Becker)

Seabirds were surveyed for 5 hours on 20 April in excellent conditions between stations 22 and 23 off the continental shelf. Once again, Cape Petrels dominated the species assemblage off the shelf, with Southern Fulmar also relatively abundant. It was a fairly slow day for sightings and there were not many birds overall. There were no prions, Blue Petrels or Wilson's Storm Petrels. The big surprise was seeing penguins just as we approached station 23. They swam about 200 m in front of the ship and were difficult to identify. Unlike Adélie Penguins that usually feed in association with sea ice, Chinstrap Penguins are typically found in open water and have been seen offshore in this area during a recent summer LTER cruise. Considering their small size, open water habitat, and a brief glimpse of white on the cheek of one bird, these penguins were most likely Chinstrap Penguins. It is interesting that penguins have now been seen three times during transits off the shelf break in limited survey time in this area. Chinstraps feed on a higher percentage of fish and are able to feed in lower light conditions that Adélie Penguins. Perhaps these birds are responding to an ephemeral system driven by the late fall blooms we have been seeing off the shelf. Also surprising was the sighting of a Sooty Shearwater in the survey and on the deck of the ship. Sooty Shearwaters are Sub-Antarctic breeders that generally move further north (they are quite common in the summer off the Pacific Coast of North America) in the austral winter.

After surveying, morphometric measurements were taken from a Sooty Shearwater and a Southern Fulmar on the deck, but no regurgitated stomach contents were found near the birds.

At station 22, a 1-m ring net tow for surface zooplankton was taken which collected a thick diatom sludge with amphipods, copepods, and krill also in the mix.

A summary of the daytime survey results is the following:

Species (common name)	Species (scientific name)	Number observed
Cape Petrel (“Pintado Petrel”)	Daption capense	41
Southern Fulmar	Fulmarus glacialoides	18
Antarctic Petrel	Thalassoica antarctica	4
Blue Petrel	Halobaena caerulea	0
Unidentified Prion		0
Grey-headed Albatross	Diomedea chrysostoma	1
Wilsons Storm-petrel	Oceanites oceanicus	0
Unidentified Skua		1
Snow Petrel	Pagodroma nivea	3
Southern Giant Petrel	Macronectes giganteus	4
Sooty Shearwater	Puffinus griseus	1
Chinstrap Penguin (probable)	Pygoscelis antarcticus	3-5
Antarctic Tern	Sterna vittata	0
Antarctic Fur Seal	Arctocephalus gazella	0

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

MOCNESS tow #7 was conducted in the early evening on April 20 in deep water (>3000 m) off of the shelf at station 23. The tow was conducted to 1000 m depth. Except for the continuing problem of the failure of the net response, all systems worked well and it was a very successful tow. Mytophids were collected from 800-200 m. The lowest depth stratum, 800-1000 m, contained chaetognaths, krill, and copepods in very low abundance especially considering the large volume of water filtered. Copepods were abundant also in the 600-800 m depth range and from 50-200 m. Euphausiids were observed from 100-600 m, but not in high abundance and they were not Euphausia superba. Amphipods were seen from 100-200 m and in the upper 25 m. The 25-50 m depth interval was dominated markedly by algae, with no other taxa being notable. Salps were seen in the 50-100 m depth interval.

On 20 April, BIOMAPER-II was towyod to 250 m on the transits between stations 21, 22, 23, and 24. During the late night transit between stations 21 and 22, upon leaving the continental shelf, an extensive region of high backscatter ranging from ~160 to 260 m depth was observed. On the transit to station 23 after completing the work at station 22, an internal wave was highlighted on 120, 200, and 420 kHz echograms at 90 to 130 m below the surface. It had 10 m wave heights (trough to crest which showed up as thin layers of alternating high and low backscattering. Shortly after, lots of individual fish like targets appeared in the down looking echograms in the 150 to 220 m depth range on the four lower frequencies, but their appearance was ephemeral and for much of the transit, there were no fish-like targets and the backscattering in the surface layers was very low. At greater depths (250 to 320 m), there was only a diffuse backscattering that showed on the 43, 120 and 200 kHz echograms. Before reaching station 23, another set of internal waves appeared and about an hour later two good sized acoustic patches, which might have been krill, were displayed between 120 and 250 meters below the surface on all 4 lower frequencies. One patch was about 70 meters tall by 500 m in horizontal extent, the other had an irregular vertical extent and a 5-pointed star-like appearance, with a horizontal extent on order 1000 m.

Scattering was sparse for a good portion of the transit from station 23 to 24 with only moderate scattering in the near surface layer on the 120 kHz echogram. With the approach to the continental shelf, a little more scattering showed up on the down looking 43 and 120 kHz echograms starting at about 180 meters below the surface.

Cheers, Peter