Variations in bioturbation across the oxygen

Oxygen minimum zones are expected to alter substantially the nature, rates and depths of bioturbation along continental margins, yet these e!ects remain poorly studied. Using excess 210Pb pro"les, sediment X-radiography and box-core samples for macrofauna, we examined bioturbation processes at six stations (400, 700, 850, 1000, 1250 and 3400 m deep) along a transect across the oxygen minimum zone (OMZ) on the Oman margin. Bottom-water oxygen concentrations ranged from &0.13 ml l~1 at 400 m to &2.99 ml l~1 at 3400 m. 210Pb mixed-layer depth and bioturbation intensity (D) exhibited high within-station variance, and means did not di!er signi"cantly among stations. However, the mean mixed-layer depth (4.6 cm) for pooled OMZ stations (400}1000 m depths, 0.13}0.27 ml l~1 bottom-water oxygen) was half that for stations from similar water depths along well-oxygenated Atlantic and Paci"c slopes (11.1 cm), suggesting that oxygen stress reduced 210Pb mixing depth on the Oman margin. Modal burrow diameter and the diversity of burrow types at a station were highly correlated with bottom-water oxygen concentration from the edge to the core of the Oman OMZ (Spearman's rho*0.89, p)0.02), suggesting that these parameters are useful proxies fo