Assuming a constant rate of quartz accumulation for deep-sea sediment core Y69-106P, from the Panama Basin, I have estimated the age of samples from the core and have constructed a curve for sedimentation-rate versus time. Stratigraphic controls for the calculated time scale include three C 14 measurements, the extinction of the radiolarian Stylatractus universus , correlation with oxygen-isotope curves from other dated cores, and an Ar 40 /Ar 39 age determination. The model sedimentation rates, when combined with data on mineralogic composition, allow the determination of accumulation rates for CaCO 3 , opaline SiO 2 , and remaining “detritus.” Fluctuations in CaCO 3 accumulation rates over time correlate with variations in oxygen-isotope ratios in biogenous carbonate from two other equatorial Pacific cores; high oxygen-isotope ratios correlate with high CaCO 3 accumulation rates. Opaline SiO 2 accumulation rates reflect changes in the dominance of different radiolarian fossil groups, changes which can be related to surface circulation in the Panama Basin. Spectral analysis of the accumulation rate of CaCO 3 in core Y69-106P and of the oxygen-isotope record of core V28-238 indicates a 23,000-yr periodicity. Spectral analysis of the opal accumulation rate suggests a 100,000-yr periodicity, which is an important frequency in the oxygen-isotope record. Both these periodicities are close to those found in fluctuations in the Earth’s orbital parameters. The eccentricity of the orbit fluctuates with an average period of 98,000 yr, and the precession of the equinoxes changes with a period of 22,000 yr.

Abstract The Falkland Trough is a west-east bathymetric deep that separates the Falkland Plateau from the North Scotia Ridge in the western South Atlantic. It lies in the path of Circumpolar Deep Water flowing within the Antarctic Circumpolar Current (ACC), and Weddell Sea Deep Water flowing beneath the ACC east of Shag Rocks passage. Marine geophysical and sediment core data demonstrate the influence of ambient bottom currents on deposition in this area, and reveal two styles of contourite sedimentation: (1) deposition of glauconite-rich sandy contourites in exposed areas of the Falkland Plateau and Falkland Trough, where vigorous ACC bottom currents control sedimentation, and (2) deposition of biogenic sandy contourites, muddy contourites and hemipelagites (western Falkland Trough), and muddy diatom ooze (eastern Falkland Trough), in the form of two elongate sediment drifts, which have developed in the presence of more sluggish bottom currents. The drift sediments contain a depositional record of bottom current flow through the glacial cycle (southern-origin bottom water flow in the east, and probably ACC flow in the west); analyses of core data from the western Falkland Trough suggest a reduction in bottom current strength during the Last Glacial Maximum at present depths of > 2500 m below sea level.