| As an important component of the global ocean, the Antarctic Bottom Water (AABW) plays pivotal roles in the meridional overturning circulations and its formation, circulation and change is a key process in global ocean. The Dense Shelf Water (DSW) sinks downslope and mixes with the Circumpolar Deep Water (CDW), forming the AABW. Three regions around Antarctica have been previously documented as the AABW production regions, and the ocean west to Cape Darnley was found as another AABW source recently. However, whether the Prydz Bay is another AABW source remains a mystery until now. Repeat hydrographic surveys data and historical data since 1970s, and the Southern Ocean State Estimate (SOSE) model output from 2005 to 2010 were used to reveal distributions and changes of AABW in the Prydz Bay and the region near Cosmonaut Sea. A series of data, including the hydrographic surveys from 1978 to 2015, the hydrographic data measured by Conductivity Temperature Depth-Satellite Relay Data Loggers (CTD-SRDLs) mounted on elephant seals deployed from 2004 to 2014, the time series data from mooring system in 2012, and the EAR-interim wind data,were used to reveal the distributions and changes of shelf water and the connection between the Shelf Water (SW) and AABW in the study region.The newly found AABW source near Cape Darnley is confirmed, however, there are no AABW locally formed in northern slope of the Prydz Bay. Relative small freshening of 0.005/decade is found in the deep ocean off Cape Darnley, which fits well to a gradually reduced freshening pattern in AABW from the Ross Sea to the Weddell Sea. The largest freshening happened in the Ross Sea and significant freshening is found in the deep ocean off Adelie Land, and no significant salinity trend occured in the Weddell Sea. The ridge extended from Cape Darnley prevents lateral mixing of AABW in deep basin. The bottom water west of the ridge is mostly formed in the Weddell Sea without significant salinity change in recent 20 years, while the bottom water east of the ridge has significant freshening trend and likely comes from the Australian Antarctic Basin. The AABW from the Weddell Sea dominates the bottom water in the Prydz Bay region with fractions about 50%-80% except the region near Princess Elizabeth Trough (PET). SOSE data advise that the main source of AABW in the Prydz Bay region is from the Weddell Sea (about 72%). The model suggests that a net loss of AABW in the Prydz Bay region, indicating strong mixing between AABW and CDW in the region.The spatial pattern of the properties of the SW in the Prydz Bay was presented, based on the CTD data and instrumented seal data. In Spring, Summer and Fall, the high salinity SW(S>34.6) is observed in the central and northern part of the Amery Basin, which is like to be caused by the CDW intrusion, and the shift of sea surface wind could have the primary impact to the CDW intrusion. The southward water transport caused by the east wind can bring the CDW into the shelf and lead to the salinity increase. In winter, there could be less CDW intrusion because of the ice cover in the sea surface, which are supported by the mooring data. The high salinity SW will flow south into the Amery Basin along the shelf and is unlikely to form the overflow DSW, explaining why the high salinity SW can not locally form AABW in northern slope of the Prydz Bay. There is Ice Shelf Water (ISW) colder than -2℃ on the Fram Bank in the western of the Prydz Bay, suggesting it is the mian outflow area of the ISW from Amery Shelf. A dense water mass with low salinity, low temperature and high oxygen was observed on the shelf break in the 70.5°E section. According to the hydrographic data, the water can form overflow DSW and flow downslope to west, which can be observed in the bottom of slope near 1500m in the 70°E section. The water will form AABW if it can flow downslope to the deep basin and keep mixing with the CDW, implying a new type of the overflow DSW in the Prydz Bay, which provides a new thinking to study the AABW formation in the Prydz Bay. |
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