Mud waves in the Argentine Basin and their relationship to regional bottom circulation patterns

Abstract

Multi-narrow beam echosoundings from the central Argentine Basin of the South Atlantic Ocean define orientations of abyssal mud waves over an area of 100,000 km 2. Mud wave heights vary from <10 m to >80 m, and wave spacings vary from 1 to more than 10 km, with typical values of 4–6 km. Sub-bottom reflectors demonstrate that many of these bed forms have migrated with time. At least four distinct mud wave fields can be identified. Mud waves on the southern flank of the Ewing sediment drift strike northwest and migrate toward the northeast (upslope). Waves on the northern Zapiola Drift strike northeast and migrate toward the southeast. A field of symmetrical and/or relict waves with variable orientations lies between the Ewing and Zapiola Drifts. Mud waves on the southwestern flank of the Zapiola Drift strike west-northwest and migrate north-northeast (upslope). Wave orientations vary with respect to the regional contours, bottom slope and flow direction; however, bottom current flow directions are poorly defined. Analysis of historical bottom photographs from the Argentine Basin suggests that bottom currents locally flow around the sediment drifts. Sediment drifts and mud waves are best developed offshore where surface eddy activity is less intense and bottom flows are probably steadier, both in speed and direction. Mud waves require 10's or 100's of thousands of years to develop. Thus the waves reflect a long-term response to environmental conditions rather than a short-term response to discrete events.