Figure 4: Dual contributions of DSW from Cape Darnley and Prydz Bay to CDBW.

θ–S diagram showing regional water masses (AASW, Antarctic surface water; AABW, Antarctic bottom water; DSW, dense shelf water; mCDW, modified circumpolar deep water and mSW, modified shelf water). Proposed mixing pathways for DSW/mSW from Prydz Bay (shaded blue–grey) and Cape Darnley (red–grey), with the depth-varying properties of offshore mCDW (diamonds and light-grey shaded area) to produce CDBW. Standard neutral density contours broadly delineates the mCDW (28.00<γⁿ<28.27) from the AASW and the DSW/mSW/CDBW. All elephant seal data from 2011 to 2013 (Fig. 1) are shown as light-grey points. Dark-grey points are from BROKE-West, a shelf break/offshore summertime survey in 2006 from 30 to 80° E. DSW (Fig. 3) is found along the near-surface freezing point (black line) from Barrier Bay (green dots), MacKenzie Bay (blue dots) and Cape Darnley (red dots) polynyas. Bottom properties in Prydz Channel (from Fig. 3b), north of MacKenzie Bay, are shown as open black squares. White diamonds indicate mean properties from BROKE-West in the 100 m thick bottom layer of mCDW on the shelf break and continental slope at 70° E. Inverted triangles show bottom mSW values from elephant seals on the continental slope north of Cape Darnley¹⁰ (Fig. 3a, depth >800 m, θ<−0.8), split into saline (>34.6) values west of 69° E (light red) and fresher (<34.6) values east of 69° E (light blue). Data from M3 (magenta dots, 2,582 m) and M4 (cyan dots, 1,798 m) mooring data¹⁰, as indicated on Fig. 1.