A series of transient global warming events (“hyperthermals”) in the early Eocene is marked by massive environmental and carbon cycle change. Among these events, the impacts of the Paleocene Eocene Thermal Maximum (~56 Ma), Eocene Thermal Maximum 2 (~54 Ma) and Eocene Thermal Maximum 3 (~53 Ma) are relatively well documented, but much less is known on the many later hyperthermals that apparently occurred on orbital eccentricity maxima until at least the end of the Early Eocene Climatic Optimum (EECO; ~53­–49 Ma). Here, at Ocean Drilling Program (ODP) Site 959 (Equatorial Atlantic Ocean), we report a large negative carbon isotope excursion (CIE) in both organic and carbonate substrates that we correlate to the “V” event sensu Lauretano et al. (2016) (or C22nH1 sensu Sexton et al. (2011)) at ~49.7 Ma, following combined bio- and chemostratigraphic constraints. Through TEX86 paleothermometry, we reconstruct a sea surface temperature rise of 1.1–1.9 ºC associated with this CIE, which, combined with evidence for warming from the deep sea, implies that this event indeed represents a transient global warming episode like the earlier hyperthermals. Organic walled dinoflagellate cyst assemblages indicate a productive paleoceanographic background setting, likely through regional upwelling, which alternated with episodes of stratification. Warming reconstructed across V at Site 959 is relatively similar to the higher-latitude-derived deep ocean reconstructions. However, the presence of upwelling and its variable intensity across the event compromises the use of the reconstructed warming as an estimate for the complete tropical band.

Climate and carbon cycling during the Eocene were complex, as inferred from records of stable isotopes and carbonate accumulation in marine sediment sections. Following a now well-documented early Eocene interval characterized by extreme global warmth and numerous short-term C-cycle perturbations documented in many sediment sections across the world, the ‘warmhouse’ climate state of the middle-late Eocene remains far less studied. In particular, the middle Eocene was punctuated by an event of significant global warming and seafloor carbonate dissolution (Middle Eocene Climate Optimum or MECO, ca. ~40.5 Ma). Over the last decade, studies from multiple sites in the Atlantic have suggested another abrupt and transient (and potentially a hyperthermal) warming event seemingly associated with a C-cycle perturbation at ~41.5 Ma, referred to as the Late Lutetian Thermal Maximum (LLTM). While both MECO and LLTM punctuate the post-EECO long-term cooling, their isotopic expression and duration are fundamentally different. At present, a dearth of continuous middle Eocene chemostratigraphic records limits our understanding of warming events like MECO and especially, the global extent of the LLTM. In this study, we develop an isotope stratigraphy of Lutetian-Bartonian age sediments from three different sites in the southwest Pacific region, two of which were drilled during IODP Expedition 371 in the Tasman Sea and a third that derives from field work in New Caledonia. We identify long-term changes in carbon and oxygen isotope records, possibly related to 405 Ky eccentricity cycles, and identify the stratigraphic expression of the LLTM and MECO. These new middle Eocene chemostratigraphic records from the southwest Pacific help to establish the global nature and relevance of multiple warming events that occurred during the ‘warmhouse’ climatic conditions of middle Eocene and highlight the utility of sedimentary carbon isotopes as a tool for chemostratigraphy and deciphering causes of past global changes.

A transient period of climate change, characterized by a global warming of ~2.5–5°C followed by a cooling to pre-excursion conditions, occurred during the last 300 kyr of the Maastrichtian (~66.34–66.02 Ma). This instability may have played a role in destabilizing marine and terrestrial ecosystems, priming the system for abrupt extinction at the K-Pg boundary, likely triggered by a large bolide impact. This pre-K-Pg warming event has often been linked to the main phase of Deccan Trap volcanism, however large uncertainties associated with radio-isotopic dating methods of basalts, along with low sedimentation rates and hiatuses in many studied sedimentary sequences, have long hampered a definitive correlation. To complement recent advances in dating of the traps, we have generated the first complete and highest resolution (2.5–4 kyr) benthic stable δ13C and δ18O record for the final million years of the Maastrichtian using the epifaunal foraminifera species Nuttallides truempyi from ODP Site 1262, Walvis Ridge, South Atlantic, calibrated to an updated orbitally-tuned age model. We then compare our data to other previously published geochemical data from other sites in the high, middle, and low latitudes. Our data confirms that the onset of the warming event coincides with the onset of the main phase of Deccan volcanism, strongly suggesting a causal link. Furthermore, spectral analysis of our extended late Maastrichtian-Early Eocene record suggests that the onset of the warming event corresponds to a 405-kyr eccentricity minima, in contrast to many transient warming events (hyperthermals) of the Paleogene, suggesting a control by orbital forcing alone is unlikely. A peculiar feature of the event, compared to other hyperthermals, is a muted carbon cycle response during warming, which may be related to the comparatively heavier δ13C signature of volcanogenic CO2 (–7‰), compared to other sources of light carbon invoked to explain Paleogene hyperthermals. The warming event coincided with minor extinctions of thermocline-dwelling foraminifera, along with dwarfing and blooms of the opportunistic disaster genera Guembelitria, suggesting that Deccan-induced climatic instability may have played a role in priming high-stress ecosystems which were tipped over a threshold into mass extinction during bolide impact.