The Pliocene–Pleistocene climate transition offers an opportunity to study the effect of glaciation on the ocean–climate system. We present a Globigerinoides ruber δ 18 O record from Ocean Drilling Program Site 1208 (Kuroshio Current Extension; KCE). This exclusively (sub)tropical foraminifer, a summer/fall mixed-layer dweller at the KCE, affords the first long (3.0Ma to 1.8Ma) orbital-scale (2.5-kyr time step) account of the sea surface in this area. The section's temperature-corrected benthic foraminiferal δ 18 O record constrains global changes in ice volume, yielding a Δδ 18 O record that primarily reflects summer/fall KCE hydrography (temperature and salinity). A 0.3‰ decrease in Δδ 18 O values at 2.7Ma coincides with the onset of Northern Hemisphere glaciation, indicating as much as 1.5°C warming during the summer/fall to suggest that the subtropical North Pacific sea surface provided heat and moisture for expanding ice sheets. On the orbital scale, the 41-kyr cycle that dominates high-latitude climate is absent from the Δδ 18 O record, indicating a stable surface water hydrographic regime on this time scale. Rather, the Δδ 18 O record varies at and is coherent with the 19-kyr precessional component of the regional insolation curve, supporting a direct response to subtropical insolation and insensitivity to extra-regional forcing factors, such as ice sheets.