Fig. 1. Schematic of the Antarctic continental margin water masses. (A) A vertical section of water masses over the Antarctic Shelf, Slope and Rise. The black rectangle shows the approximate position of the KACTAS/KAOS surveys. Sub-panels (B) and (C) show the seasonal variability in the surface layer between winter and summer.

Fig. 2. The KACTAS and KAOS study region. Top panel: Mac Robertson Land and Amery Basin (55–85E, 60–72S). The Enderby Basin, Princess Elizabeth Trough (PET), Kerguelen Plateau (KP), Amery Ice Shelf (IS) and Prydz Bay (PB) as shown. Study area (shown in bottom panel) indicated by red box. Bottom panel: Continental shelf and slope offshore from the Mawson coast, East Antarctica (61–65E, 66–67S). CTD locations are shown as filled circles (black=KACTAS; grey=KAOS). Storegg Bank and Béchervaise Island (B.I.) are as shown. Bathymetric contours from the General Bathymetric Chart of the Oceans (GEBCO), 2000 edition.

Fig. 3. (A) Hydrographic survey of KACTAS and KAOS, offshore from Mawson (61–65E, 66–67S). Bathymetric contours from GEBCO. Repeated transect for KACTAS (stns. 2–9, panel B) and KAOS (stns. 4–9, panel C) are as shown. For KAOS, the southern end of the transect is repeated (stns. 18–21, in grey).

Fig. 4. Ship-borne ADCP currents at 100 m for KACTAS (above) and KAOS (below), with a vertical section of the east/west (+ve/-ve) component of the current for the repeat meridional transect (black line). Current speed range shown on vertical colour bar: top panels, ; bottom panels, .

Fig. 5. θ–S diagram for (A) KACTAS and (B) KAOS. Potential temperature in C. Potential density (σ_θ, ) as shown with major water masses and a schematic of the γ_n contours for the Orsi et al. (1995) water-mass boundaries (thick black lines). Thin dashed black line is the surface freezing temperature.

Fig. 6. Vertical sections of salinity, θ (C) and dissolved oxygen from KACTAS (14–15 January 2001) and KAOS (13–14 January 2003). Black dashed lines are the seasonal mixed-layer depth (upper) and base of the T_min layer (lower).

Fig. 7. As in Fig. 6, but for log₁₀ CTD fluorescence in the top 100 dbar only. White dashed line is the seasonal summer mixed-layer depth.

Fig. 8. Mixed-layer depths from KACTAS and KAOS. Top panels (A) KACTAS mixed-layer depths, (B) KACTAS transects. Coloured dashed lines for January 2001 dates: 14–15th (black); 16–17th (blue); 18th (cyan); 19–20th (red); and 20–21st (magenta). Bottom panels (C) KAOS mixed-layer depths, (D) KAOS transects. Coloured lines for January 2003 dates: 15–16th (black); 24–25th (blue); and 30th (cyan).

Fig. 9. (A) AVHRR Satellite imagery for January in each survey (indicated by red rectangle: left—KACTAS; right—KAOS). Images courtesy of CSIRO. (B) Monthly anomalies of sea-ice concentration from passive microwave estimates (Comiso, 1990) for the December preceding each survey over the period 1997–2005. Arrows indicate ice motion vectors from SSM/I (Fowler, 2003, updated 2005) for each December. (C) Time-series of mean sea-ice concentrations over the study area for both surveys.

Water mass properties from KACTAS and KAOS

Shown are (a) salinity, (b) potential temperature (C), (c) potential density , (d) dissolved oxygen , (e) fluorescence (uncalibrated), depth-averaged over the mixed layer (0.1 σ_θ criterion) and T_min layer (0.1 σ_θ to ).