DECIPHERING THE SEDIMENTARY RECORD ON THE PIEDRA BUENA TERRACE ALONG THE SOUTHERN ARGENTINE MARGIN

The southern Argentine margin is composed of a series of four terraces that are shaped by the interplay between strong Southern Ocean currents, terrigenous sediments transported through canyons, and alternating carbonate and siliceous biogenic inputs. Here, we examine the sedimentary records deposited along the Piedra Buena terrace between 2200 and 2500 m water depth. The biogenic input is dominated by coccolithophorid and planktonic foraminiferal components during peak interglacial intervals versus diatoms and radiolaria for other times. The position of the southern polar front driven by orbital climate cycles determines the biogenic composition in the cores. Sea-level cycles provide one control on the downslope terrigenous input with higher terrigenous components in the Piedra Buena cores during the glacial intervals. However, the sedimentary record in the Piedra Buena cores is strongly influenced by the vertical migration of deep-water currents, Upper Circumpolar Deep Water for the Piedra Buena terrace, which sweep across this drift. Grainsize measurements show increasing velocity along this terrace during the glacial intervals counter to the regional pattern. This requires vertical migration of current axis because other records show the Southern Ocean currents slowed during glacial interviews relative to interglacial velocities. As a result, only the cores distal to the modern UDCW axis contain a complete sedimentary record with the Piedra Buena sedimentary drifts.