Extended Data Fig. 6: Diagram showing approach that combines mooring, model, and hydrographic data to calculate volume transport of AABW.
From: Recent reduced abyssal overturning and ventilation in the Australian Antarctic Basin
At each gateway section, the plume of AABW (blue shading) is measured by at least three repeat hydrographic stations (dashed lines) and one deep mooring (arrow symbols). The hydrographic profiles give temperature, salinity, neutral density, and oxygen as functions of latitude and pressure. The neutral density surface 28.30 kg m−3 is used to define the top of the AABW layer and is used to estimate the vertical thickness of the water mass at each latitude, H(t,y). Deep-moored current meters spanning at least one year provide time series of the cross-sectional speed of the plume at a single latitude. Neighbouring current meters provide an estimate of the vertical shear at the same latitude. The horizontal structure of the flow (bottom panel, \({{{\mathcal{F}}}}\)) is extracted from the global model at the location of the hydrographic section. \({{{\mathcal{F}}}}\) is the normalized, mean velocity within the layer denser than 28.30 kg m−3. This structure function varies with season and latitude. Multiplying the layer-mean speed of the AABW at the mooring location by the normalized structure function gives the speed of the AABW layer as a function of latitude (\(v{{{\mathcal{F}}}}={v}_{AABW}\)). This product is multiplied by H and integrated by latitude to calculate volume transport (TV), as \({T}_{V}=\int\,[v(t){{{\mathcal{F}}}}(t,y)]\)\(\times H(t,y)dy\). The calculation is repeated for each available hydrographic section, where t is the occupation, to yield a time series of TV.
