Deep inflow into the Mozambique Basin

More than 200 conductivity-temperature-depth (CTD) stations were worked aro und the Southwest Indian Ridge and Del Cano Rise as part of the World Ocean Circulation Experiment. A selection of these data provides information abo ut the inflow of bottom water into the Mozambique Basin. The basin is close d below 3000 m, yet the inflow is significantly large, of order 1 Sv (1 Sv = 10(6) m(3) s(-1)). Estimates of the basin-scale upwelling at 4000 m sugge st that the vertical velocity is also large, 10 x 10(-5) cm s(-1) or more, an order of magnitude greater than global ocean estimates. Examination of t he characteristics of the bottom water in the Mozambique and Agulhas Basins and the Prince Edward Fracture Zone shows that bottom water enters the Moz ambique Basin from the Agulhas Basin and also directly from the Enderby Bas in. Most of the transport enters the Mozambique Basin via the Agulhas Basin , where two regions of northward flow below 4000 m are found. The major flo w, on the eastern flank of the Mozambique Ridge, is through and above the d eep, extending (5900 m) trench that connects the Agulhas and Mozambique Bas ins. The second; weaker flow enters the Transkei Basin along the deep easte rn flank of the Agulhas Plateau, then turning east into the Mozambique Basi n. The only source of bottom water to the Agulhas Basin is the Enderby Basi n, but a more direct route between the Enderby and Mozambique Basins exists via the Prince Edward fracture, which extends deeper than 4000 m throughou t its length and links the two basins directly across the Southwest Indian Ridge. Full depth CTD stations trace the changing characteristics of the de ep and bottom water in the fracture, and moored current meter data show the strength and persistence of the throughflow. Strong mixing with the overly ing deep water elevates the salt content of the bottom water by comparison with the other water in the Mozambique Basin. Thus two distinct bottom wate rs of the Mozambique Basin originate in the same place (the Enderby Basin), and their different characteristics are solely a function of the routes th ey have taken and the processes encountered along the different pathways.