ALBERT

Description: A GO-SHIP hydrographic section I07S along nominally 55ºE south of 30ºS to the ice edge was occupied in the 2019/20 austral summer for the first time. The bottom water masses in the eastern part of the Weddell-Enderby Basin is a mixture of four potential source waters from the Weddell Sea (WSDW), the Cape Darnley (CDBW), off Adelie Land coast (ALBW), and the Ross Sea (RSBW). The contribution of these four sources in the bottom water observed across the I07S section was estimated by multiparameter mixing analysis using Conserve Temperature, Absolute Salinity, quasi-conservative PO, NO, and SO (phosphate, nitrate, and silicate combined with dissolved oxygen with the Redfield ratio for deep water), and planetary potential vorticity. The result is somewhat sensitive to the choice of the source water properties in the well-mixed ACC Bottom Water densities but robust for the bottom water masses denser than 28.27 kg/m³ neutral density. The dominant source is CDBW near the bottom (〉 28.30 kg/m³) and WSDW above, with near-shore contribution from ALBW and RSBW. Once the composition is known, it is possible to estimate the apparent age of the source waters by minimising the difference between observed tracers (CFC-11, CFC-12, CFC-113, and SF6) and tracer concentration calculated from the prescribe composition with varying ventilation years. With an assumed saturation rate of 0.7, the estimated apparent source ages are in a range of 40 to 60 years with younger water toward the bottom and on the slope.