Limnology and ecology of lakes along the S?ya Coast, East Antarctica

The Soya Coast in East Antarctica has several ice-free areas where many small （〈1 km2） and shallow （〈50 m depth） glacial lakes display various limnological features. Geological, biological, and ecological studies conducted by the Japanese Antarctic Research Expeditions since 1957 are reviewed herein. Most of the lakes along the coast are oligotrophic; however, water quality is highly variable depending on differences in lake morphology and history. Geophysical and paleolimnological studies suggest that most of the lakes appeared after the Last Glacial Maximum （LGM） and have since maintained a lacustrine condition. The ubiquitous occurrence of benthic microbial assemblages with low phytoplankton biomasses is a common feature of other Antarctic lakes. However, diverse benthic assemblages such as moss pillars and large pinnacle microbial structures are found in the lake basins. Frequent and continuous limnological studies have revealed three typical water circulation patterns, underwater light climate features （too much light, which includes UV radiation during the ice free season）, and the structure of benthic assemblages based on their photosynthetic physiology. The phenomenon of mass floatation of benthic assemblages was observed in a lake during the ice-covered season; this was explained by seasonal environmental conditions. Thus, a hypothesis was formulated based on ecological matter cycling, eutrophication, and lake succession processes.

Observation and Data Archiving System of a Superconducting Gravimeter at Syowa Station, Antarctica

A superconducting gravimeter (SG, model TT70#016, GWR Instruments) was deployed for the first time in Antarctica in 1992 at Syowa Station. Observations began in April 1993. Although the SG was equipped with a 10 K cryocooler, its liquid helium (LHe) required refilling twice a year to maintain its superconducting state. The LHe was produced by a separate helium liquefier. After continuous gravity measurement with the SG for 11 years, it was replaced by a second SG (CT#043) with a 4 K cryocooler in December 2003 in order to reduce loads of person in charge for LHe production. Because the manufacturer could not supply a replacement 4 K cryocooler, this SG ceased measurement in November 2009. In January 2010, a new superconducting gravimeter (OSG#058) was installed and had recorded high-quality gravity time series with data acquired every second for more than five years without interruption. Because the personal computer (PC) controlling the observation and data acquisition is connected with PCs in Japan through an Intelsat satellite communication link, we can check the status of observations in real time. It is also possible to fix remotely certain problems with the gravimeter. The observed gravity data are transferred daily to a data server in Japan. Also included in the upload are diagnostic data of the gravimeter such as the temperature of the coldhead and environmental data such as atmospheric pressure. Plots of the daily data are publicly available. The raw data with a 1 s sampling interval are also released to registered researchers. The released gravity time series along with the environmental data are greatly useful for investigating solid earth dynamics especially in the long period bands. We provide necessary information to use these long-range data sets.

Stenian A-type granitoids in the Namaqua-Natal Belt,southern Africa,Maud Belt,Antarctica and Nampula Terrane,Mozambique:Rodinia and Gondwana amalgamation implications

We carried out SHRIMP zircon U-Pb dating on A-type granitic intrusions from the Namaqua-Natal Province,South Africa,Sverdrupfjella,western Dronning Maud Land,Antarctica and the Nampula Province of northern Mozambique.Zircon grains in these granitic rocks are typically elongated and oscillatory zoned,suggesting magmatic origins.Zircons from the granitoid intrusions analyzed in this study suggest^1025-1100 Ma ages,which confirm widespread Mesoproterozoic A-type granitic magmatism in the Namaqua-Natal(South Africa),Maud(Antarctica)and Mozambique metamorphic terrains.No older inherited(e.g.,~2500 Ma Achean basement or^1200 Ma island are magmatism in northern Natal)zircon grains were seen.Four plutons from the Natal Belt(Mvoti Pluton,Glendale Pluton,Kwalembe Pluton,Ntimbankulu Pluton)display 1050-1040 Ma ages,whereas the Nthlimbitwa Pluton in northern Natal indicates older 1090-1080 Ma ages.A sample from Sverdrupfjella,Antarctica has^1091 Ma old zircons along with^530 Ma metamorphic rims.Similarly,four samples analysed from the Nampula Province of Mozambique suggest crystallization ages of^1060-1090 Ma but also show significant discordance with two samples showing younger^550 Ma overgrowths.None of the Natal samples show any younger overgrowths.A single sample from southwestern Namaqualand yielded an age of^1033 Ma.Currently available chronological data suggest magmatism took place in the Namaqua-Natal-MaudMozambique(NNMM)belt between^1025 Ma and^1100 Ma with two broad phases between^1060-1020 Ma and 1100-1070 Ma respectively,with peaks at between^1030-1040 Ma and^1070-1090 Ma.The age data from the granitic intrusions from Namaqualand.combined with those from Natal,Antarctica and Mozambique suggest a crude spatial-age relationship with the older>1070 Ma ages being largely restricted close to the eastern and western margins of the Kalahari Craton in northern Natal,Mozambique.Namaqualand and WDML Antarctica whereas the younger<1060 Ma ages dominate in southern Natal and western Namaqualand and are largely restricted to the southern and possibly the western margins of the Kalahari Craton.The older ages of magmatism partially overlap with or are marginally younger than the intracratonic Mkondo Large lgneous Provinee intruded into or extruded onto the Kalahari Craton,suggesting a tectonic relationship with the Maud Belt.Similar ages from granitic augen gneisses in Sri Lanka suggest a continuous belt stretching from Namaqualand to Sri Lanka in a reconstituted Gondwana,formed during the terminal stages of amalgamation of Rodinia and predating the East African Orogen.This contiguity contributes to defining the extent of Rodinia-age crustal blocks,subsequently fragmented by the dispersal of Rodinia and Gondwana.