Multi-proxy reconstruction of late Maastrichtian surface-ocean dynamics in the tropical Pacific

The Late Cretaceous greenhouse climate experienced a pronounced cooling trend during the Campanian–Maastrichtian, potentially driven by declining atmospheric CO₂ and ocean-gateway reorganization. Yet, low-latitude high-resolution reconstructions remain limited, hampering mechanistic interpretations of surface-ocean dynamics. Here, we present a new high-resolution planktonic Mg/Ca-derived sea-surface temperature (SST) record from Ocean Drilling Program (ODP) Sites 1209 and 1210 (Shatsky Rise, western tropical Pacific), spanning ~2.5 Myr (67.0–69.4 Ma). Reconstructed SSTs range between ~32 and 34 °C, consistently exceeding modern tropical surface-ocean temperatures. SSTs rise toward ~68.1 Ma before cooling in the youngest part of the record. While absolute Mg/Ca temperatures are higher than published TEX₈₆ and planktonic δ¹⁸O-based SSTs, the major trends agree across proxies. To place these SST changes into a broader paleoceanographic framework, we integrate our record with new high-resolution planktonic δ¹³C and δ¹⁸O data from the same sites. The combined dataset enables evaluation of carbon-cycle perturbations, surface-water salinity variability (δ¹⁸O_sw), and productivity-related vertical δ¹³C gradients, as well as their pacing on orbital timescales. Together, these results refine Maastrichtian low-latitude climate variability and highlight a trend toward increased meridional temperature gradients.