A simple method for estimating phytoplankton abundance using a surface seawater monitoring system off Syowa Station during austral summer

A surface seawater monitoring system was used aboard the Shirase to estimate phytoplankton abundance while the icebreaker was anchored in an ice covered area off Syowa Station during the austral summer of 1996/97. A significant positive relationship was observed between the digital output (OP) values of the chlorophyll fluorometer of the system, and chlorophyll a (Chl a) concentrations of the seawater that passed through the system. Using this relationship, OP values were converted into Chl a (Chl a OP). Throughout the present study, the Chl a OP was found to be consistent with temporal changes in Chl a observed in the field near the Shirase, with high Chl a OP values measured in relatively warm and less saline water. These findings suggest that the high Chl a may be derived from the ice-edge phytoplankton blooms that develop in stable waters associated with melting ice. Relatively simple operation without need for complicated maintenance procedures facilitates the ease with which the system can be used. The operation of the system every summer may facilitate the acquisition of data that reveal the long-term variability of phytoplankton biomass under fast ice

Photosynthetic characteristics of phytoplankton off Adelie Land, Antarctica, during the austral summer

The photosynthesis-irradiance characteristics (P-E curves) and quantum yields of natural phytoplankton were investigated in the Southern Ocean off Adelie Land, Antarctica, during the austral summer. Data were acquired at eight stations during a cruise of T/V Umitaka-Maru III. The photosynthetic P-E curves showed low light adaptation of phytoplankton. Mean value (±standard deviation) of the P-E curve parameters, α^*, and I_k, were 0.014 (±0.013) mgC (mg chl. α)^ h^1 (μmol photons m^ s^)^ and 76 (±55) μmol photons m^ s^, respectively. Although phytoplankton were adapted to low irradiance, the phytoplankton in the SCM were not fully adapted to the low irradiance prevailing at those depths. P^*_ in the studied region was low (mean of 0.66 (±0.37) mgC (mg chl. α)^ h^) and generally lower than the previously reported values in waters near the Antarctic Peninsula. The maximum quantum yield varied widely, ranging from 0.001 to 0.038mol C (mol photons absorbed)^ at the surface and from 0.007 to 0.092mol C (mol photons absorbed)^ near the bottom of the euphotic zone. These values were within the range of published data. Comparison of photosynthetic parameters with historical data indicated that primary productivity from remotely sensed data for the whole of the Southern Ocean, based on these field estimates of photosynthetic parameters, has been overestimated

Distribution of Copepoda along 140°E in the Indian sector of the Southern Ocean

NORPAC net samplings at three stations along a south-north transect on ca. 140°E were conducted in the Indian sector of the Southern Ocean from March 10 to 12 in 2002 during the 43rd Japanese Antarctic Research Expedition. The survey was held to examine the community structure and abundance of Copepoda in the seasonal ice zone of the Southern Ocean. A total of 15 species of copepod were identified at the stations. For nine species of copepod, Microcalanus pygmaeus, Calanus simillimus, Rhincalanus gigas, Euchaeta antarctica, Clausocalanus laticeps, Scolecithricella minor, Metridia lucens, Haloptilus oxycephalus and Oithona frigida, disparities of the distributions between the south of the Southern Boundary (SB) and the north became apparent. As here was a distinct difference of, about 2°C, in the sea surface temperature between the south and north of the SB, these disparities were considered to be influenced by the difference in the physical structure in the ocean, in particular by the water temperature, which was driven by the SB. Among Calanoides acutus, Calanus propinquus, and R. gigas, the earlier copepodite stages were observed at higher latitudes at all stations. This trend was considered to be a result of the sea ice retreat, which caused a later spawning period for Copepoda. In addition, an interaction between the sea ice conditions and the community structure of copepod along 140°E was suggested

Unusual abundance of appendicularians in the seasonal ice zone(140°E ) of the Southern Ocean

During the 43rd Japanese Antarctic Research Expedition(JARE) cruise on March 10-12 in 2002, NORPAC net samplings at three stations along a south-north transect, ca. 140°E in the Indian sector were conducted to survey zooplankton community structure and abundance in the seasonal ice zone(SIZ) of the Southern Ocean. A total of fourteen species/taxa were identified from the three stations. While copepods were numerically dominant at two stations(79.9% and 93.1% respectively of total abundance), appendicularians were found to be numerically dominant(84.0% of total abundance) at the southernmost station. This dominance of Appendicularia at this station suggested that Appendicularia is possibly an integral part of the community structure of the zooplankton in the SIZ. The Southern Boundary(SB) on the 140°E transect was found to be located at ～64.30°S and the southernmost station was located south of the SB while the two other stations were located north of the SB. Some species, such as Rhincalanus gigas, Calanus simillimus, Amphipoda, Euphausiacea, and Polychaeta, had distribution patterns that correlated with the position of the SB, therefore the SB is considered important in influencing the distribution of the zooplankton and its community structure in the SIZ

Photosynthetic physiology and primary productivity of phytoplankton in the Australian sector of the Southern Ocean

第2回極域科学シンポジウム　共通セッション「海氷圏の生物地球化学」 11月16日（水） 統計数理研究所 3階セミナー