Volume transport and property distributions of the Mozambique Channel

We summarize previous estimates of volume transport and property distributions through the Mozambique Channel and offer additional estimates and measurements based on recently acquired hydrographic and float data. Previously published property distributions are consistent with southward spreading through the Channel. Waters of the Mozambique Channel are characterized by shallow and intermediate oxygen minima separated by a relative maximum. Based on hydrographic sections, the intermediate maximum in dissolved oxygen is seen to decrease in value as it spreads southward. The highest values are found in the westward flow of the South Equatorial Current just north of Madagascar and within the western 200 km of the Channel. Similarly, oxygen concentrations at the intermediate oxygen minimum, which derives from the Arabian Sea, increase southwards, while its depth increases from 900 to 1100 m, supporting previous studies and indicating southward spreading and mixing along the Mozambique Channel. Historical transports based on hydrographic data in the Channel vary from 5 Sv northward to 26 Sv southward depending on reference level and time of the year. Balancing transport below 2500 m (the sill depth in the Channel), we estimate the net southward transports above this depth to be 29.1 and 5.9 Sv for the northern and southern sections, respectively - the difference is presumably related to seasonality and eddy variability superimposed on the mean flow. Individual deep float trajectories show the presence of many eddies, but the overall flow in the channel is southward, and broadly consistent with hydrography. Model outputs also show mean southward transport with considerable seasonal variability. Satellite data show high variability in sea surface height anomalies and high eddy kinetic energy associated with eddy activity. Although the geostrophic transport values are consistent with the historical limits, the lowered ADCP measurements suggest a substantial barotropic component to the flow. Direct long-term measurements of the current are needed to quantify its magnitude and variability.