International Ocean Discovery Program (IODP) Site U1490 in the Western Pacific Warm Pool (05°48.95ʹN, 142°39.27ʹE, 2341 m water depth) provides the opportunity to directly compare an astronomically tuned benthic foraminiferal isotope cyclostratigraphy with biostratigraphic datums and paleomagnetic reversals over the interval 13.7 to 8.6 Ma as well as to reconstruct the evolution of intermediate-deep water masses across the middle to late Miocene Carbonate Crash. The astronomically tuned delta 18O derived ages for magnetochrons identified between 13.6 and 9.3 Ma during IODP Expedition 363 are in good agreement (mean deviation of 17 ±4 kyr) with ages reported in the Geomagnetic Polarity Time Scale of the Geologic Time Scale (GPTS2020), except over the interval 11.7 to 11.0 Ma that is characterized by poorly defined magnetization. The delta 18O based astrochronology at Site U1490 also closely matches that from Ocean Drilling Program (ODP) Site 1146 in the South China Sea and IODP Site U1443 in the equatorial Indian Ocean, allowing evaluation of middle to late Miocene changes of inter-ocean intermediate to deep water delta 13C gradients on orbital timescales. An increase in the delta 13C gradient between Sites 1146 and U1490 from ~12.4 to 10.4 Ma suggests that changes in Pacific Ocean circulation contributed to carbonate depletion during the Carbonate Crash. After 10.5 Ma, a decrease in the meridional delta 13C gradient between Sites U1490 and 1146 indicates spreading of a more uniform central Pacific intermediate-deep water mass, exhibiting similarity to the equatorial Indian Ocean deep water mass at Site U1443. Improved preservation of thin-walled foraminiferal tests and increases in sedimentation rates and coarse fraction percentages mark the recovery of the marine carbonate system and the onset of the Biogenic Bloom after ~9.3 Ma.
