Abstract

Calcium carbonate dissolution patterns were determined for portions of the past 2.5 m.y. in 9 Eltanin piston cores distributed along the Southeast Indian Ridge in the Southeast Indian Ocean. Oxygen isotope and foraminiferal faunal records were used to determine the relationship between paleoclimate water-mass changes and the dissolution intervals. CaCO3 dissolution was generally more intense during glacial periods, but dissolution pulses of short duration also occur during several interglacial periods, particularly on the shallower portions of the Southeast Indian Ridge. The glacially related increases in dissolution are in-phase with northern migrations of the Polar Front. During the past 250,000 yr, the Polar Front has migrated to 45°S latitude in the region south of Australia and as far north as 40°S in the mid-southern Indian Ocean during the same time period. From the mid-Brunhes chron to the present, an over-all increase in CaCO3 content indicates a gradual deepening of the carbonate lysocline. Unlike the Brunhes chron, the carbonate fluctuations in the Matuyama age cores are due mainly to productivity variations as a function of water-mass migrations, and are of lower magnitude than are the Brunhes fluctuations. The magnitude of the oxygen isotopic fluctuations in the Matuyama chron is also smaller than it was during the Brunhes chron, suggesting less climatic variability.

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