Abrupt conclusion of the late Miocene-early Pliocene biogenic bloom at 4.6-4.4 Ma

What caused the end of the high ocean productivity in the tropics in late Miocene-early Pliocene is debated. Here, deep-sea sediment records reveal that productivity abruptly declined 4.6 million years ago, potentially linked to reduced seasonality and monsoon intensity that led to decreased nutrient supply to the oceans. The late Miocene-early Pliocene biogenic bloom was an extended time interval characterised by elevated ocean export productivity at numerous locations. As primary productivity is nutrient-limited at low-to-mid latitudes, this bloom has been attributed to an increase or a redistribution of available nutrients, potentially involving ocean-gateway or monsoon-related mechanisms. While the exact causal feedbacks remain debated, there is even less consensus on what caused the end of the biogenic bloom. Here, we compile Mio-Pliocene paleoproductivity proxy data from all major ocean basins to evaluate the timing and pacing of this termination. This systematic analysis reveals an abrupt and sustained reduction in low-latitude ocean productivity at 4.6-4.4 Ma. The decline in productivity coincided with a prolonged period of low orbital eccentricity and a shift towards lower-amplitude obliquity, an astronomical configuration linked to reduced East Asian Monsoon intensity and decreased riverine nutrient supply.