Atsushi Tanimura

Temporal variability of particulate flux in the northern Bering Sea

Observations of downward particulate flux were carried out in the main depocenter of the Chirikov Basin in the northern Bering Sea between 20 June and 24 September 1988 using a time series sediment trap. A total of 12 samples, each representing an 8 day period, were collected at the mooring depth of 36 m where the bottom depth was 49 m. Total POC flux varied between 253 and 654 mg C m−2day−1. Relatively low C/N ratios (4.9–7.4) indicated a fresh organic matter supply to benthic communities. The mean organic carbon flux (501 mg m−2 day−1) is comparable to the estimated organic carbon utilization (464 mg m−2day−1) at the sediment surface (Grebmeier and McRoy, 1989 Marine Ecology Progress Series, 53, 79–91), suggesting a close correspondence between the particulate flux and the benthic demand of the Chirikov depocenter.

Assemblages of necrophagous animals off Enderby Land, East Antarctica

A hyperbenthic baited trap was deployed at three sites in Lutzow-Holm Bay and off Enderby Land, Antarctica, in the 1993/1994 summer to investigate the species composition, distribution, and abundance of necrophagous animals. The trap consisted of four chambers, with a length of 100 cm and a diameter of 38 cm. The sample at the abyssal site, 3,186 m deep, contained 74 individuals of 6 species, completely different from that at the other 2 sites on the continental shelf; it was dominated by the large amphipod Eurythenes gryllus, a cosmopolitan species recorded from bathyal to abyssal depths. The species composition of the continental shelf sites, 93–137 individuals of 10–12 species, was dominated by species endemic to Antarctica, such as the small amphipod Pseudorchomene coatsi and the isopod Natatolana meridionalis; in these continental shelf sites, a high degree of species diversity was observed.

Postembryonic development ofParalabidocera antarctica (I. C. Thompson) (Copepoda, Calanoida) from the fast ice near Syowa Station, Antarctica

Six nauplius and five copepodid stages as well as adults ofParalabidocera antarctica (I. C. Thompson, 1898) (Copepoda:Calanoida) are described based on specimens obtained from fast ice and collected by a plankton net near Syowa Station (69°00′ S, 39° 35′ E), Antarctica. The adult male and female are redescribed in detail. Nauplius stages ofP. antarctica are very similar to the previously describedAcartia species. Sexual dimorphism becomes apparent from copepodid IV onwards in the morphology of antennule and leg 5. The copepodid stages of this species retain certain characteristics not only of Acartiidae but also of Pontellidae and Parapontellidae.

Change in habitat of the sympagic copepod Paralabidocera antarctica from fast ice to seawater

Abstract. The occurrence and age structure of an Antarctic ice-associated copepod, Paralabidoceraantarctica, were investigated using a light trap under fast ice near Syowa Station. Sampling was carried out between May and November 1984. P. antarctica were found in high numbers in the traps on 1–2 and 23–24 November. No copepods were found in any trap between May and October. The timing of the absence and occurrence of P. antarctica in the light traps coincided with their ice-dwelling and pelagic life-phases. More than 99% of the total catch was taken in the traps set in the water immediately below the ice in both sampling periods on 1–2 and 23–24 November. The age structure of the P. antarctica populations consisted of copepodite stage III (CIII) to adult and IV (CIV) to adult, respectively. The earlier population was dominated by CIV and CV and the later one by adults. The behavior pattern of P. antarctica is suggested to be controlled by phototactic and thigmotactic traits, and their habitat change from sea ice to seawater may occur by trade-off between two behavioral traits with the acquisition of swimming ability.

Spatial Patterns in Nutrient and in vivo Fluorescence Distributions in the Marginal Ice Zone and the Seasonally Open Oceanic Zone in the Indian Sector of the Antarctic Ocean, in Austral Summer

Surface temperature, salinity, concentrations of silicate (Si) and nitrate + nitrite (N), and in vivo fluorescence (Fluor) were investigated in the marginal ice zone (MIZ) and the seasonally open oceanic zone (SOOZ) (32–40°E, 64–69°S) from February 23 to 28 1992. In the MIZ the mean Si and N were 67.8 ± 2.2 μM and 32.5 ± 1.7 μM, respectively. There was a trend that low N values coincided with high Fluor values. Observation conducted at one point (64°S, 38°E) revealed a diel variation pattern in Fluor. Applying this pattern of deviation from noon value, all Fluor data were normalized to value at local noon. In the MIZ a significant negative correlation was observed between the normalized Fluor and N but not Si. On the other hand, Si decreased continuously from south to north in the SOOZ and was negatively correlated with the normalized Fluor. Difference in Si concentration was about 30 μM between the sea around 64°S and the MIZ, while the difference in N concentration was estimated as less than 10 μM. If diatoms take up silicate and nitrogen at an approximate ratio of 1:1, additional nitrogenous nutrients other than nitrate and nitrite (e.g. ammonia, urea etc.) would be required. In this case, an f-ratio of lower than 33% is obtained. It is suggested that in the MIZ abundance of phytoplankton community dominated by non-diatom increases utilizing nitrate while in the SOOZ abundance of phytoplankton community dominated by diatoms increases consuming Si and regenerated nitrogen.