ALBERT

Description: Highlights • Accurate age model during Pliocene for site U1490 established • Co-variant nutricline depth and productivity in WPWP throughout Pliocene • Deeper nutricline and lower productivity during 4.8–3.5 Ma linked to CAS closure • Nutricline shoaling during 3.5–3.0 Ma due to restriction of Indonesian Seaway Abstract The tropical Pacific played an important role in modulating global climate change during the Pliocene. Studies of tropical Pacific sea surface temperatures covering the period from the Pliocene onwards indicate that changes in the thermal mean state over the tropical Pacific can significantly influence global climate feedbacks and connect the high- and low-latitude climates. Tropical productivity fluctuations are a significant mechanism with respect to the operation of the global carbon cycle. Yet, temporal changes in primary productivity are not well constrained in the western Pacific warm pool (WPWP), where the ocean–climate system is not dominated by upwelling systems. Furthermore, the role of nutricline dynamics in forcing productivity over tectonic timescales remains uncertain. Here we use relatively high-resolution foraminiferal carbon isotope records combined with Ba/Ti ratios obtained from International Ocean Discovery Program (IODP) Site U1490 in the WPWP to reconstruct nutricline depth and paleoproductivity over the period 5.1–2.6 Ma. Our records imply that nutricline and productivity variations were closely coupled over tectonic timescales, implying that the dynamics of the nutricline play a significant role in regulating productivity in the WPWP. The deeper nutricline and lower productivity during 4.8–3.5 Ma might have been fostered by the closure of the Central American Seaway through the thickening of the mixed layer in the WPWP. We relate the overall shallower nutricline and increased productivity during 3.5–3.0 Ma to the restriction of the Indonesian Seaway via the enhanced influence and upwelling of high-latitude southern-source waters.