Equatorial Indian Ocean productivity over the last 200,000 years and links to deep circulation variations

Abstract

Ocean circulation plays a key role in regulating atmospheric carbon dioxide levels during Pleistocene glacial-interglacial cycles. However, spatial responses of the oceans remain poorly constrained because reliable records from important carbon exchange regions, such as the equatorial Indian Ocean, are scarce. Here we show environmental magnetic records from the western equatorial Indian Ocean spanning the past 200,000 years. The magnetic signals primarily reflect variations in magnetofossils, the magnetic remains of magnetotactic bacteria, with higher abundances during interglacials. Combined with geochemical indicators, these records reveal enhanced productivity associated with increased nutrient availability during warm periods. Productivity variations closely follow glacial-interglacial cycles and reflect changes in deep ocean circulation. Glacial carbon burial resulted from reduced productivity caused by expanded Antarctic Bottom Water and enhanced stratification, which suppressed the upward transport of deep-sourced nutrients and carbon dioxide. In contrast, weakened Antarctic Bottom Water influence during warm interglacials strengthened deep-surface exchange, enhancing productivity and contributing to carbon dioxide release. Deep circulation changes driven by Antarctic Bottom Water regulate equatorial Indian Ocean productivity and carbon cycling across glacial-interglacial cycles over the past 200,000 years, as shown using environmental magnetic records from the western equatorial Indian Ocean.