Fine-grained sediment waves on the western flank of the Zapiola Drift, Argentine Basin: evidence for variations in Late Quaternary bottom flow activity

Abstract

Extensive fields of deep-water sediment waves, which drape the flanks of the Zapiola Drift in the central Argentine Basin, provide a record of the long-term stability of bottom water flow patterns. Combining observations from a dense grid of high-resolution narrow-beam echosounder data with results of wave growth modelling confirms that a southward current is responsible for the wave geometry on the western flank of the drift. This flow seems to be the western part of an anticlockwise gyre, which is centred around the Zapiola Drift. The regional variation of accumulation rates on the drift flank suggests that the flow velocity gradually decreases upslope. To the north–east of the drift crest, flow velocities increase again, causing a southwestward migration of the crest itself. Changes in the internal geometry of the sediment waves show evidence for variations in flow intensity during the last ∼100 kyr. Four different periods of alternating higher and lower flow velocities can be identified with fluctuations between 10 and 20 cm/s. This caused erosion, non-deposition and deposition on the downslope wave flanks.