Morphology of abyssal mudwaves at project MUDWAVES sites in the Argentine Basin

Extensive fields of mudwaves are present in the Argentine Basin. Mudwaves and water parameters at three sites were studied to provide detailed information on bathymetry, mudwave structure, sediment parameters and bottom water flow characteristics. Two sites, 5 and 6, are discussed in this paper. Crests of mudwaves at Site 5 on the north flank of the Zapiola Drift are oriented 45° anti-clockwise from the measured westward flow direction and migrate to the left of the flow direction. Mudwaves at Site 6 on the south flank of the Zapiola Drift are oriented 20° anti-clockwise from the inferred southeast bottom flow direction, and also migrate to the left of direction. Evidence from current meters and surface sediments suggests that the mudwaves at Site 5 are active today, while those at Site 6 have been active in the Holocene, but perhaps not within the last 100 years. Mudwave orientation anti-clockwise to mean flow, preferential sediment accumulation on the left wave flank, and apparent sediment accumulation on the wave crest agree with a model for mudwave growth presented by Blumsack and Weatherly (1989, Deep-Sea Research, 36, 1327-1339). Cross-wave asymmetry in sediment accumulation pattern is sufficient to cause a 10% change in surface sediment bulk density over the wave profile. The record of mudwave migration obtained from Sites 5 and 6 in the southern Argentine Basin and from Site 7 in the northern Argentine Basin suggests that bottom water flow has changed over a number of time scales during the last 200,000 years. Thus the analysis of abyssal bed forms can provide independent evidence about past changes in bottom flow.