Introduction

Oxygen depletion is widespread in the world oceans (Kamykowski & Zentara 1990), occurring as permanent, seasonal and episodic features. Persistent low oxygen is evident in midwater oxygen minimum zones (OMZs), defined as regions where oxygen concentrations are 0.5ml l1 (or about 7.5% saturation; 22M). These features are sometimes called oxygen minimum layers or oxygen-deficient zones, and are present at different water depths ranging from shelf to upper bathyal zones (10-1300m). Oxygen minima are created through biochemical oxygen consumption, with circulation affecting their distribution and position within the water column (Wyrtki 1962). Where oxygen minima intercept the continental margin or seamounts, they have large effects on benthic assemblages.