CCAMLR

The climate of tile Western Antarctic Peninsula (WAP) region is distinguished by large seasonal and interannual variability and by the occurrence of seasonal sea ice which changes the ocean-atmosphere interface, affects tile surface albedo, and modifies the annual temperature cycle. Air temperature records for several peninsula stations have been examined, and the annual progression of surface air temperatures show an along-peninsula gradient indicative of a contrasting influence of maritime versus continental climatic regimes. WAP temperature records show the largest and most significant warming trends for the Antarctic with mid-winter temperature increases of 3° to 5°C over the past half-century. Increased temperature variability in fall and winter is linked to tile high interannual variability of sea ice coverage. Linear regression analysis shows a significant (99.9%) anti-correlation between air temperature and sea ice extent, even after accounting for serial correlation in the two time series. There are distinct seasonal lead/lag relationships between temperature and sea ice in this region, which underscore the complexity of polar feedback mechanisms. The more than 45 year Faraday air temperature record shows a significant (95% confidence level) correlation with the Southern Oscillation Index (SOI) and coherences between both temperature and sea ice with the SOI suggest teleconnections between the WAP and lower latitudes. This evidence suggests that the WAP area, the focus of the Palmer Long-Term Ecological Research program, is sensitive to climate variability. Consequently, because of strong coupling between temperature, sea ice and the antarctic marine ecosystem, the Palmer LTER is ideally located for the study of ecological responses to global change.

Feeding behavior of Antarctic krill (Euphausia superba) on salps was observed through onboard experiments during 1994/95 Kaiyo Maru Antarctic Ocean research cruise. Feeding rate was more than 1 salp/krill/day. Among 4 items of ethanol extracts; salps, phytoplankton, krill, and polychaets, krill preferred salps best. This evidence implies that the substances extracted from salps were most attractive to krill. The result of our experiment might indicate a tight ecological relationship between krill and salps. Since salps have ability to ingest wide size range of particles, there might also be a possibility of link between microbial loop and krill through salps.

Observations on abundance of by-catch fishes were made during the austral summer months of 1995 (from 30 January to 18 February) on board F/V Niitaka Maru to the north of the South Shetland Islands. Among 78 hauls examined, a total of 97 specimens of fishes belonging to five species, Electrona antarctica, Electrona carlsbergi, Protomyctophum tenisoni, Krefftichthys anderssoni and Notolepis coatsi, were found in 20 trawl catches. Juvenile or adult notothenioid fishes were never found in a random sample of 50 kg of krill. Number of by-catch fishes ranged from 0 to 50 per 100 kg of krill catch and total wet weight of by-catch fishes also ranged from 0 to 248.2 g per 100 kg of krill catch. Abundance of by-catch fishes was higher in krill hauls with the low catch rates.

Distribution and biomass of salps and Antarctic krill (Euphausia superba) were investigated near the South Shetland Islands during austral summer 1990-1991. Salp biomass ranged between 0 and 556 mgC•m-3 and was greatest at a station in the Bransfield Strait in late December 1990. Salp biomass was lower than that of E. superba. Two species of salps; Salpa thompsoni and Ihlea racovitzai were found, and the former was dominant numerically. Spatial distribution and generation composition of these two species was different. Spatial distributions of salps and E. superba did not overlap particularly so the January-February period. While E. superba was found mainly in the coastal area which showed high-chlorophyll a values, salps exhibited high biomass in the oceanic area with low chlorophyll a concentrations. Predation by salps on small krill and the competitive removal of food by them, are discussed as potential reasons for the relatively low abundance of E. superba at the stations where salps were present in great numbers.

This paper demonstrated the relationship between sea-level air pressure gradients in Drake Passage and krill recruitment variabiIlty. Years of high pressure gradients coincided with the years of good krill recruitment, and vice versa.