The “greenhouse” climates of the Paleocene and Eocene have formed the focus for many proxy and modelling studies in recent decades, as they are the closest geological analogues for our future warmer anthropogenic world. Yet, the long-term evolution of ocean temperature and carbonate chemistry at orbital-resolution, especially at low latitudes, are still poorly constrained. Here we present new orbital-resolution foraminiferal trace metal (Mg/Ca & B/Ca) records spanning the late Paleocene to early Eocene (~58–53 Ma) from a new splice between ODP Site 758 and IODP Site U1443, Ninetyeast Ridge, northern Indian Ocean. We generated coupled Mg/Ca and B/Ca records from well-preserved mixed layer and thermocline-dwelling planktic foraminifera, and benthic foraminifera deposited at a shallow palaeo-water depth (~1500 m), to construct temperature change and carbonate chemistry (related to pH and DIC concentration) across a water column depth transect above Ninetyeast Ridge. Our new trace metal records are the first long-term orbital-resolution records of their kind from the poorly studied Indian Ocean. We estimate both the magnitude of long-term warming and associated carbonate chemistry change from the late Paleocene–early Eocene, as well as the magnitude of change on orbital (405- & 100-kyr) timescales. In addition, a portion of the Paleocene-Eocene Thermal Maximum is resolved in our records, providing a critical minimum constraint for the magnitude of temperature and carbonate chemistry change within the low-latitude Indian Ocean during this hyperthermal event.

The current study presents new bed-by-bed brachiopod δ13C and δ18O records from Öland, Sweden, which together with previously published data from the East Baltic region, constitutes a high-resolution paired brachiopod and bulk rock carbon and oxygen isotope archive through the Lower to Upper Ordovician of Baltoscandia. This new dataset refines the temporal control on the global Ordovician δ18O-trend considerably, improving paleoenvironmental reconstructions through the main phase of the Great Ordovician Biodiversification Event (GOBE). The new brachiopod carbon and oxygen isotope records from Öland display strong similarity with the East Baltic records, elucidating the regional consistency as well as global correlation utility of the ensuing composite Baltoscandian Early to Middle Ordovician carbon and oxygen isotope record. The carbon isotope record from Öland indicates that prominent carbon cycle perturbations are recorded in both brachiopods and bulk carbonates, most notably the MDICE (Mid-Darriwilian Carbon Isotope Excursion). The oxygen isotope record reveals a long-term Early to Late Ordovician trend of increasingly heavier brachiopod δ18O values, with a pronounced increase during the Middle Ordovician Darriwilian Age. We interpret this trend as dominantly reflecting a paleotemperature signal indicating progressively cooler Early to Middle Ordovician climate with glacio-eustasy. Our Baltic δ18O values are therefore consistent with postulations that the biotic radiations during the GOBE and climatic cooling during the Darriwilian were strongly linked.