Quaternary carbonate record from the equatorial Indian Ocean and its relationship with productivity changes

The CaCO3 content in Quaternary deep-sea sediments from Pacific and Atlanti c oceans have been suggested to respond differently to glacial/interglacial cycles; CaCO3 contents are highest during glacials in the Pacific but high est during interglacials in the Atlantic Ocean. It is not yet clear as to w hether a Pacific or an Atlantic pattern of CaCO3 fluctuations dominates the Indian Ocean. We have analyzed the Ocean Drilling Program (ODP) Site 709A from the western equatorial Indian Ocean for the last 1370 ka to determine the relationships between percentages and fluxes of CaCO3 and Quaternary pa leoclimatic changes. We also analyzed the coarse (> 25 mu m) and fine (< 25 mu m) fractions of CaCO3 in an attempt at estimating the influence of diff erences in productivity of foraminifera and calcareous nannofossils in shap ing the CaCO3 record. Carbon isotopes and Ba/Al ratios were used as indices of productivity. Percentages and fluxes of CaCO3 in the total sediment and < 25 mu m fraction do not show any clear relationships to glacial/intergla cial cycles derived from delta(18)O Of the planktonic foraminifera Globiger inoides ruber. This indicates that CaCO, fluctuations at this site do not s how either a Pacific or an Atlantic pattern of CaCO3 fluctuations. Fluxes o f CaCO, (0.38 to 2.46 g cm(-2) ka(-1)) in total sediment and Ba/Al ratios ( 0.58 to 3.93 g cm(-2) ka(-1)) show six-fold variability through the last 13 70 ka, which points out that productivity changes are significant at this s ite. Fluxes of the fine CaCO3 component demonstrate a 26-fold change (0.02 to 0.52 g cm(-2) ka(-1)), whereas the coarse CaCO3 component exhibit eight- fold change (0.13 to 1.07 g cm(-2) ka(-1)). This suggests that productivity variations of calcareous nannofossils are greater in comparison with the f oraminifera. On the other hand, mean values of coarse CaCO3 fluxes are high er compared to those of fine CaCO3, which reveals that the foraminifera con tribute more to the bulk CaCO3 flux than the calcareous nannofossils in the equatorial Indian Ocean. (C) 1999 Elsevier Science B.V. All rights reserve d.