Carbonate sedimentation beneath the Antarctic Circumpolar Current during the late Quaternary

Abstract

Calcium-carbonate content and planktonic foraminiferal fragmentation have been studied in four late Quaternary “Eltanin” piston cores (E48-22, E48-28, E49-18 and E49-23) taken from the Southeast Indian Ridge between 3200 and 3400 m waterdepth beneath the Antarctic Circumpolar Current. The calcium-carbonate records in the two southernmost cores, E49-18 and E49-23, show distinct glacial—interglacial cycles, with the glacial intervals and intermediate cool intervals having low carbonate values relative to the interglacial times. However, the carbonate records of E48-22 and E48-28 are largely independent of the paleoclimatic records, and may be influenced by input of volcanic ash from the St. Paul or Amsterdam Islands located less than 700 km upwind of the cores. Planktonic formainiferal fragmentation, considered to be a dissolution index, indicates that dissolution generally increased during glacial intervals relative to the interglacial intervals in E49-18 and E49-23. In E48-22 and E48-28, the dissolution records do not follow glacial—interglacial patterns, but instead dissolution was greatest during oxygen isotope stage 9, the stage 9 8 boundary, the early part of stage 8, and during stage 7. No relationship exists between benthonic formainiferal changes and the fragmentation records in three cores (E48-22, E48-28 and E49-23), indicating that deep-water circulation changes had minimal or no influence on these dissolution records. However, in E49-18 the benthonic foraminiferal and the dissolution records are closely matched from oxygen isotope stages 12 to 5 ( t = ∼440,000–120,000 yrs B.P.). Deep-water circulation changes may have influenced the dissolution record in E49-18, or the two variables may be unrelated, but may have independently responded to glacial—interglacial climatic changes.