Near-bottom currents over the continental slope in the Mid-Atlantic Bight

From a set of 28 current meter records we have found that near-bottom currents faster than 0.2 m s-1 occur frequently over the outer continental shelf of the Mid-Atlantic Bight (bottom depth <210 m) but very rarely (<1% of the time) between bottom depths of 500 m and 2 km over the slope. The rarity of strong near-bottom flow over the middle and lower slope allows the accumulation of fine-grained sediment and organic carbon in this region. Fast near-bottom currents which do occur over the slope are invariably associated with topographic waves, although it is often superimposed inertial oscillations which increase current speed above the level of 0.2 m s-1. Episodes of intense inertial oscillations occur randomly and last typically for 10-20 days. Their energy source is unknown. Topographic wave energy exhibits a slight, but statistically significant, minimum over the mid-slope. These waves appear irregularly and vary both along isobaths and in time. The irregularity is presumably a consequence of random topographic wave generation by Gulf Stream instability. The current regime within sea-floor depressions in the slope (canyons and gullies) is distinctly different from that of the open slope; most notable is the near absence of topographic wave motion within depressions.