Strong export of Antarctic Bottom Water east of the Kerguelen plateau

Abstract

Deep western boundary currents east of the Antarctic Peninsula and the Kerguelen plateau are important pathways for transporting deep Antarctic water masses to the global ocean. An array of moored current meters, used to quantify the water transport in this system, reveals a flow that is stronger than any measured in a deep western boundary current at similar depths so far. The primary paths for the transport of Antarctic Bottom Water from the Southern Ocean into the global ocean are the deep western boundary currents east of the Antarctic Peninsula and the Kerguelen plateau1. Previous ship-based observations documented distinct water properties and velocities associated with a deep western boundary current in the Kerguelen region2,3,4,5,6,7, but the mean flow is as yet unconstrained. Here we report measurements from a coherent array of eight current-meter moorings that reveal a narrow and intense equatorward flow extending throughout the water column just east of the Kerguelen plateau. Velocities averaged over two years exceed 20 cm s−1 at depths of about 3,500 m, the strongest mean deep western boundary current flow yet observed at similar depths. We estimate the mean equatorward transport of water colder than 0 ∘C at 12.3±1.2×106 m3 s−1, partially compensated by poleward flow. We also estimate the net equatorward flow of water colder than 0.2 ∘C at about 8×106 m3 s−1, substantially higher than the 1.9×106 m3 s−1 reported from the boundary current that carries dense water from the Weddell Sea into the Atlantic Ocean north of the Falkland plateau8. We conclude that the Kerguelen deep western boundary current is a significant pathway of the global ocean’s deep overturning circulation.