The Middle to Late Miocene “Carbonate Crash” in the Equatorial Indian Ocean

Abstract

We integrate benthic foraminiferal stable isotopes, X‐ray fluorescence elemental ratios, and carbonate accumulation estimates in a continuous sedimentary archive recovered at International Ocean Discovery Program Site U1443 (Ninetyeast Ridge, Indian Ocean) to reconstruct changes in carbonate deposition and climate evolution over the interval 13.5 to 8.2 million years ago. Declining carbonate percentages together with a marked decrease in carbonate accumulation rates after ~13.2 Ma signal the onset of a prolonged episode of reduced carbonate deposition. This extended phase, which lasted until ~8.7 Ma, coincides with the middle to late Miocene carbonate crash, originally identified in the eastern equatorial Pacific Ocean and the Caribbean Sea. Interocean comparison reveals that intense carbonate impoverishment at Site U1443 (~11.5 to ~10 Ma) coincides with prolonged episodes of reduced carbonate deposition in all major tropical ocean basins. This implies that global changes in the intensity of chemical weathering and riverine input of calcium and carbonate ions into the ocean reservoir were instrumental in driving the carbonate crash. An increase in U1443 Log (Ba/Ti) together with a change in sediment color from red to green indicate a rise in organic export flux to the sea floor after ~11.2 Ma, which predates the global onset of the biogenic bloom. This early rise in export flux from biological production may have been linked to increased advection of nutrients and intensification of upper ocean mixing, associated with changes in the seasonality and intensity of the Indian Monsoon.

Monsoons, Upwelling, and the Deoxygenation of the Northwestern Indian Ocean in Response to Middle to Late Miocene Global Climatic Shifts

“…Their assumption is in contradiction with Dickens and Owen (, 1994), who, using multiple lines of evidence, illustrate the presence of increased productivity in the Indian Ocean at least from 9 Ma and up to 5 Ma. This proposed “biogenic bloom” in the Indian Ocean was recently confirmed and is now proposed to have started even earlier (~11.2 Ma) by Lübbers et al () in the eastern Indian Ocean (Site U1446; Figure ).…”

“…Interestingly, the increase in biogenic silica burial at Site 722B occurs at the same time as the carbonate crash observed at the Ninety East ridge in the Indian Ocean (Lübbers et al, 2019). At this time reduced carbonate accumulation is also recorded in the Pacific and the Caribbean (e.g., Jiang et al, 2007).…”

“…Overall, this suggests that the expansion of cold, nutrient‐rich, Antarctic deep and intermediate waters may have had a major impact on primary productivity and plankton communities along the Oman Margin, while also affecting carbonate preservation in the deeper parts of the Indian Ocean (e.g. : Lübbers et al, ). The effects of this shift in upwelling conditions are also recognized in contemporary records from other major upwelling regions such as the Benguela Upwelling system (Rommerskirchen et al, ).…”

“…Arabian Sea SST data and seasonality inference from Zhuang et al (); Foraminifera data from Keller and Baron (1983), Kroon et al (), and Gupta et al (); Oceanic isotopes data from Cramer et al (); Antarctic Ice Sheet from Flower and Kennett (); Australian Climate from Groeneveld et al (); SAM and Maldives state from Betzler et al (, 2018); southern Indian Ocean Intermediate water state from Smart et al (). Indian Ocean carbonate crash after Lübbers et al ().…”

“…Dashed colored lines indicate major paleooceanographic and climatic events during occurring during the study interval. Shaded bar underlying the Indian Ocean “biogenic bloom” sensu Lübbers et al () reflects relative upwelling intensity along the Oman Margin with darker grays corresponding to stronger upwelling (see Figure ).…”