AMLR 2002 Weekly Report No. 5

AMLR 2002 Weekly Report No. 5

10 February 2002

1. Current position is off the southwest coast of Patagonia in route to Punta Arenas for a two-day port call. Progress is slow because of gale-force northwest winds and seas. During the past month a survey of bio-geographic conditions and a census of fur seal pup production in the vicinity of the South Shetland Islands were completed. Three CTD stations out of 95 had to be cancelled due to weather; otherwise, all planned operations were successfully completed. Major equipment failures included a meteorological instrument package, a CTD, a power supply for the acoustic system, and a salinometer. Fortunately, the availability of backup instruments and spare parts precluded any loss of data. The exception was the salinometer; in this case water was saved for analysis on Leg II using another instrument shipped to Punta Arenas. Primary productivity measurements were cancelled when the shipment of C14 isotopes did not arrive inPunta Arenas prior to sailing for Leg I. Upon completion of the fur seal census, R. Hollingshead was recovered from the Copacabana field camp and R. Holt, W. Trivelpice and V. Vallejos were transferred to the CapeShirreff field camp. Subsequently two lines of stations north of Livingston and KingGeorgeIslands were re-occupied, and a net sampling station was conducted in Bismark Strait. Finally, a CTD and optical cast was made approximately 1/3 of the way across Drake Passage (see item 4).

2. The fur seal pup census. The census was completed with visits to CapeValentine, Elephant Island and Turret Point and CapeMelville on KingGeorgeIsland.Our surveys of the two sites on the south coast of King GeorgeIsland indicated fur seals had not established breeding colonies there.There were, however, several sites with suitable habitat that were occupied by large numbers of sub-adult male fur seals; but no females or pups were observed. A visit to Black Point, an ice-free cape just east ofCapeShirreff, had to be cancelled because of heavy seas. Our Chileans colleagues later reported a successful landing at Black Point two days before and they counted three live pups and one dead.In general, counts at all known colonies were similar to previous surveys in 1996 and 1992.

3. Zooplankton. With the expanded survey grid this year came the introduction of higher latitude zooplankton taxa which previously had not been encountered.This was especially true in the JoinvilleIsland area, influenced by Weddell Sea shelf water, and South Area adjacent to, and influenced by, outflow from GerlacheStrait.Notable additions to the faunal assemblage were abundant larval and juvenile fishes (e.g., Trematomusnewnesi, T. scotti, T. lepidorhinus, Prionodraco evansii, Parachaenichthys charcoti) and jellies (e.g., Zanclonia weldoni, Modeeria rotunda, Chromatonema rubra), various forms of pteropods (Clio pyramidata forma sulcata and forma antarctica), unidentified decapod larvae and "ice krill", Euphausia crystallophorias.

While identification tools at hand permitted us to identify many of the new forms, large concentrations of euphausiid larvae (primarily late calyptopis and early furcilia), particularly in the JoinvilleIsland area, created concerns.These Euphausiaspp larvae most likely were from E. crystallorophias, which is the dominant euphausiid in higher latitude, pack ice zones. Antarctic krill (Euphausiasuperba) and ice krill have similar spawning periods (December to February). Postlarval E. crystallorophias have rarely been collected, and the larvae never identified, during prior AMLR surveys. Because E. superba and E. crystallophorias larvae are similar in size and appearance there is no assurance that they were adequately separated during Survey A sample analyses. This is a serious matter as our projections about krill year class success are in part based on their larval abundance during January-March surveys. An additional sample from a region where E. crystallorophias spawning is known to occur was therefore required to establish larval identification aids for these species. This sample, collected in Bismarck Strait, made it possible for us determine species identifications of freshly caught larvae based on their pigmentation and morphometrics. This information will be extremely useful during Survey D.

4. Phytoplankton. Continuous monitoring of phytoplankton photophysiology using fast repetition rate fluorometry (FRRF, Chelsea Instruments, Inc.) connected to the ships continuous seawater flow system (intake depth of 7 meters) was done in coastal and shelf regions of the South Shetland and ElephantIslands.As an indicator of phytoplankton growth rates, Fv/Fm (variable:maximal fluorescence) indicated a diel variability. This variability corresponded to the solar cycle: maximal rates (0.5-0.6) were measured during night time, while minimal rates (0.1-0.2) measured during mid-day (1500-1900 GMT).

Additional phytoplankton and optical data were collected during our second pass of the transect containing stations 16-06, 15-07, 14-08, and 13-09. Station 15-07 had about the same chlorophyll concentrations in the water column as measured two weeks previous, while 16-06 showed a slight decrease and 13-09 showed a slight increase.

Continuous measures of phytoplankton photophysiology using FRRF connected to the ships continuous seawater flow system were also made during the southern excursion through the Gerlache Strait. For the northward transect back to Punta Arenas, hourly samples of chlorophyll and high pressure liquid chromatography were obtained from the ships continuous seawater flow system in addition to continuous measures with FRRF. These measures were made through the Polar Front. Surface chlorophyll concentrations in the Gerlache Strait were highest between AnversIsland and the Lamaire Passage, with chlorophyll concentrations reaching 21 mg m^-3, and lowest values found just south of the Polar Front with surface concentrations ranging 0.1-0.2 mg m^-3.One station midway on this survey transect (61.1ºS 68.3ºW) was made to obtain optical, photobiological and physical data of the water column.

5. Meteorology. Predominantly westerly and northwesterly winds between 10 and 35 kts prevailed with short periods of southwesterly and northeasterly weather. Winds increased in latter half of week, as a deep low pressure (974 mbar) passed by. Occasional snowfalls were experienced during the week. Air temperatures moderate 0 to 4°C and gradually increased to 6°C, in the Drake Passage. As the ship approachedSouth America northwest to north winds increased from 10 to 50 kts, with short periods up to 60 kts, accompanied by a barometer drop from 1000 to 981 mbar. Air temperature increased steadily from 6 to 9°C, during this period.