Ocean gateways and circulation dynamics: Unveiling the deep water-mass properties in the western equatorial Pacific since the Middle Miocene

Tectonically driven adjustments in the ocean gateways, such as the constriction and closure of the Central American Seaway (CAS), have been linked to the significant variations in deep water circulations across the Atlantic and Pacific Oceans in the Miocene. The changes in these tectonic gateways had substantial consequences on the Atlantic Meridional Overturning Circulation (AMOC), the Antarctic Circumpolar Current (ACC) and consequently Antarctic ice sheet growth, and deep water circulation pathways across the ocean basins. The timing of the closure of the deep water connection between the Atlantic and Pacific Oceans, through CAS, and related changes in deep water circulation in the western Pacific are still debatable. We examined foraminiferal relative abundances of epibenthic genus Cibicidoides (a synonym of Cibicides) and its stable isotopic ratios to decipher the timing of tectonically controlled changes in deep water circulation since the Middle Miocene at ODP Site 807, western equatorial Pacific. Our findings, correlated with previously published data, suggest the North Component Water (NCW) incursion from the Atlantic to the western Pacific (Site 807) via CAS between ∼12.5 and ∼ 9.5 Ma. An abrupt decrease in benthic foraminifer Cibicidoides kullenbergi at ∼9.5 Ma suggests the initiation of a significant shift in the deep water mass, coinciding with the major δ¹³C divergence between the Atlantic and Pacific oceans.