MORPHOLOGY OF ABYSSAL MUDWAVES AT PROJECT MUDWAVES SITES IN THE ARGENTINE BASIN

Extensive fields of mudwaves are present in the Argentine Basin. Mudwa ves and water parameters at three sites were studied to provide detail ed information on bathymetry, mudwave structure, sediment parameters a nd bottom water flow characteristics. Two sites, 5 and 6, are discusse d in this paper. Crests of mudwaves at Site 5 on the north flank of th e Zapiola Drift are oriented 45-degrees anti-clockwise from the measur ed westward flow direction and migrate to the left of the flow directi on. Mudwaves at Site 6 on the south flank of the Zapiola Drift are ori ented 20-degrees anti-clockwise from the inferred southeast bottom flo w direction, and also migrate to the left of the flow direction. Evide nce from current meters and surface sediments suggests that the mudwav es 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 or ientation anti-clockwise to mean flow, preferential sediment accumulat ion 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 as ymmetry in sediment accumulation pattern is sufficient to cause a 10% change in surface sediment bulk density over the wave profile. The rec ord of mudwave migration obtained from Sites 5 and 6 in the southern A rgentine Basin and from Site 7 in the northern Argentine Basin suggest s that bottom water flow has changed over a number of time scales duri ng the last 200,000 years. Thus the analysis of abyssal bed forms can provide independent evidence about past changes in bottom flow.