ABYSSAL CURRENT INFLUENCE ON THE SOUTHWEST BERMUDA RISE AND SURROUNDING REGION

Echograms (3.5 kHz) and bottom photographs reveal that the northward f lowing Antarctic Bottom Water (AABW) has strongly influenced the moder n depositional regime on the southwest Bermuda Rise. The spatial distr ibution of echo character types, the orientation and nature of current -controlled structures, and limited current meter data show that AABW flows with varying intensities along three primary pathways around and over the southwest Bermuda Rise. The main core of AABW flows clockwis e around the eastern and western flanks of the southern Bermuda Rise, roughly parallel to the 5400 m isobath. This current bifurcates at 28 degrees 30'N, 69 degrees W where a portion flows northeast over the so uthwest Bermuda Rise and the remainder continues north along the physi ographic boundary between the southwest Bermuda Rise and the Hatteras Abyssal Plain. Secondary ribbons of AABW branch off the main core of A ABW during its southerly journey along the southeastern Bermuda Rise, and flow west through fracture zones. Finally, a diffuse, northward fl owing AABW sweeps the entire southwest Bermuda Rise. A progression of current-controlled bedforms occurs beneath the main path of the AABW r eflecting the spatially varying current velocities and sediment supply . The main core of AABW flows west through the narrow Vema Gap creatin g erosional furrows along the border between the southwest Bermuda Ris e and the Vema Gap. Current velocities greater than 20 cm s(-1) are in ferred from the bedforms in this region. Farther north along the south western edge of the Bermuda Rise, sediment waves become more prevalent . This transition from erosional to more depositional bedforms results from diminished current velocities (5-15 cm s(-1)) and increased sedi ment supply. Although some of these bedforms on the southwest Bermuda Rise appear to be relict, their orientation is consistent with current meter data and abyssal current direction inferred from bottom photogr aphs.