SHI Jiuxin and ZHAO Jinping
First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China
Ninteen Chinese National Antarctic Research Expeditions (CHINARE) have been dispatched in succession since 1984. Most of these expeditions were executed by research vessels, which included marine science cruises of the Southern Ocean. After the Chinese Zhongshan Station was established in the East Antarctica in 1989, the region of Prydz Bay near the Zhongshan Station becomes one of the key areas for Chinese scientists to conduct the Southern Ocean research. Physical, chemical and biological data have been collected in this area since then and the related research work has been carried out for many years. The sea ice in the Southern Ocean has significant seasonal variation, whose variation amplitude is only less than that of the annual cycle of snow cover in the northern hemisphere in the cryoshere, which shows that sea ice in the Southern Ocean influences the global climate strongly. By using remote sensing, the long-term time series data of sea ice can be obtained. Therefore, the another interesting problem provoking the attention of Chinese scientists is the variations of sea ice in the Southern Ocean and their relations with climatic changes. In the past 8 years, great progresses in studies of the Southern Ocean have been made. The main results of Chinese scientists in the studies on water masses, circulation and sea ice in the Southern Ocean are summarized in this paper.
I. WATER MASSES AND CIRCULATION IN THE REGION OF PRYDZ BAY
With an area of about 6´104 km2, the Prydz Bay is the third large bay around the Antarctica, just smaller than the Weddell Sea and the Ross Sea. It's located in the range of 67°45¢—69°30¢S，70°—80°E, in the Indian section of the Southern Ocean. At its east bank, the Chinese Zhongshan Station（69° 22¢24¢¢S，76°22¢40¢¢E） was built in 1989. Since then, the region of Prydz Bay become a key area of Chinese Antarctic Research Expedition. Besides some data observed around the Chinese Great Wall Station（62°12¢59¢¢S，58° 57¢52¢¢W）and on the way to the Antarctica (Yang et al., 1997, for example), most oceanographic data have been collected from the fixed stations in the region of Prydz Bay. These field observations were firstly carried out as a part of survey of krill resource (Shi et al., 1995a) and then were performed for the studies of water masses and circulation.
1. Water Mass
There are 4 water masses , in the upper layer of the region, i.e. the Antarctic Surface Water (ASW), Winter Water(WW), Circumpolar Deep Water (CDW) and Shelf Water (SW). All these water masses have been found in the observed data of CHINARE (Shi and Ning, 1995; Le et al., 1996; Pu et al., 2000b). Nine meridional observed sections were designed (between 68° E and 108° E) during CHINARE-7 (1990-1991). An analysis of the CHINARE-7 data showed the following different features in both sides of 83°E due to the topographic influence of the Kerguelen Plateau (Chen et al., 1995). To the west of 83°E (i.e. in Prydz Bay and its northern area), the depth of ASW was about 20 m with its maximum depth of 30 m at the top of the bay (Zhao and Chen, 1995), and WW was located in 30-70 m, CDW was located below 70m with the maximum temperature being of 1.85-2.00°C at the center of CDW. To the east of 83°E, i.e. to the east of Prydz Bay, ASW was located in 0-30 m, WW in 50-100 m, and CDW below 100 m; the temperature at the center of CDW was lower than that in the west part with minimum of 1.04°C and maximum of 1.49°C, which indicates the stronger influence of SW to the east of 83°E. The observed sections of CHINARE-9 (1992-1993) are located between 58° and 83° E. Upwelling of CDW is found from the CTD data of CHINARE-9. The strongest upwelling is found to be in the depth of 50-200 m to the west of Prydz Bay (Yu et al., 1996b,1998). The ANARE data in the same time also showed several high temperature water blocks to the north of 66°S, which was considered as the result of the CDW upwelling (Shi and Ning, 1995). A recent analysis (Pu et al., 2002) of CHINARE-15 (1998-1999) showed that CDW extended southward in depths between100 m and 2000 m; both the high temperature core (>1.2°C) and high salinity core (>34.7) of CDW became the thickest and extended the furthest southward at section 75°E. Pu et al. (2000a) attributed the strong upwelling of CDW to the cyclonic eddies in this area. The same data also indicated the northward extension of SW (Pu et al., 2000b). The strength of SW became weaker as it extended northward. To the north of 65