Paleoenvironmental implications of the calcium isotope characteristics in the MD81349 from the Nintyeast Ridge in the Indian Ocean

A δ44Ca curve from shells of the planktonic foraminifera Globigerinoides sacculifer in calcareous biogenic oozes has been extracted from the Nintyeast Ridge in the Indian Ocean since 300 ka. By combining terrigenous inputs (e.g., grain size, magnetic susceptibility, and turbidite frequency) with the oceanic productivity (e.g., biogenic content and Neogloboquadrina dutertrei content), it is found that the curve’s variations are closely related to the historical evolution of the oceanic calcium cycle. The δ44Ca value is in lower tendency and has small oscillation during Marine Isotope Stage (MIS) 6, when the supply of terrigenous detrital is highest. In contrast, during MIS 3, 5 and 7, the δ44Ca values are in higher tendency, and their fluctuations are consistent with the variations of the productivity proxies. These results suggest that the calcium isotopes are mainly influenced by the input of the Himalayan erosion products to the northern Indian Ocean. In addition, the developmental stages of calcareous planktons may have a secondary impact on the fluctuations of the calcium isotope ratio of sea water.