when you do a google image search for the pic you get sites in chinese. searching names in chinese might get you better results. unfortunately i'm seeing multiple names used...but "Great atoll of Sands Islands" 中沙群岛大环礁 is one. anyway led me to this description (with another name) but seems to be describign the area well. ??
The deepest part of the South China Sea
Zhongsha Great Atoll is the largest atoll in the South China Sea islands, with a length of about 140 km and a width of about 55 km, extending from north to south west, slightly oval. The atolls are all submerged by seawater, and the depth is generally 9-26 metres.
According to Bi Hua, a professor at Hainan Normal University's School of Geography and Tourism, the eastern side of the Great Atoll is a deep and large crustal fault zone, with the landshell and oceanic crust coming into contact at a steep slope of 51C-58C and falling to -4000m. The waters between the twin reefs in the southern part of the Great Atoll and the Spratly Islands are the deepest in the South China Sea (-5559 m), and the heat flow, Bug gravity and magnetic forces are abnormally high and may be related to land mass drift; The west side is xisha, the middle sand trough, the depth of 2000-3000 meters;