(Figure 2) Organic carbon content, stable isotope ratios, TEX86 index and sea surface temperature reconstruction for the early Aptian of ODP Hole 198-1207B

The Cretaceous has long been recognized as a time when greenhouse conditions were fueled by elevated atmospheric CO2 and accompanied by perturbations of the global carbon cycle described as oceanic anoxic events (OAEs). Yet, the magnitude and frequency of temperature change during this interval of warm and equable climate are poorly constrained. Here we present a high-resolution record of sea-surface temperatures (SSTs) reconstructed using the TEX86 paleothermometer for a sequence of early Aptian organic-rich sediments deposited during the first Cretaceous OAE (OAE1a) at Shatsky Rise in the tropical Pacific. SSTs range from ~30 to ~36 °C and include two prominent cooling episodes of ~4 °C. The cooler temperatures reflect significant temperature instability in the tropics likely triggered by changes in carbon cycling induced by enhanced burial of organic matter. SST instability recorded during the early Aptian in the Pacific is comparable to that reported for the late Albian-early Cenomanian in the Atlantic, suggesting that such climate perturbations may have recurred during the Cretaceous with concomitant consequences for biota and the marine environment.

Calcareous nannofossils and planktic foraminiferal assemblages of ODP Hole 198-1210A

Calcareous nannofossil and planktic foraminiferal assemblages from ODP Hole 1210A in the northwestern Pacific Ocean were used to reconstruct surface-water conditions for the past 500 kyr. Stratigraphic control was provided by calcareous nannofossil events that are thought to be synchronous over a broad range of latitudes. Calcareous nannofossil and planktic foraminiferal assemblages and abundance patterns indicate the unlikelihood of long term (Milankovitch-scale) latitudinal shifts of the Kuroshio Extension over the last 500 kyr and illustrate two successive surface water-mass states, one that prevailed prior to 300 ka and one that existed after 300 ka. The relative abundance of very small placoliths and the absolute abundance of the upper photic zone (UPZ) coccolith species decrease abruptly at approximately 300 ka. The relative abundance of the lower photic zone (LPZ) species Florisphaera profunda greatly increases at the same time, although intervals during which the relative abundance of this taxon is very low or absent also occur prior to 300 ka. The absolute abundance of planktic foraminifera gradually increased after the 300-ka boundary, including peaks of Globoconella inflata. These assemblage and abundance changes suggest significant modifications to the surface water-mass structure. Surface water was weakly stratified prior to 300 ka, but alternated between intensely stratified and vertically mixed after 300 ka. Changes in the surface water-mass structure suggest an intensification of the East Asian summer and winter monsoon after 300 ka.

Benthic and planktic foraminiferal stable isotope records combined with Nd isotope ratios of ODP Hole 198-1210B

The Pacific Ocean is the largest water body on Earth, and circulation in the Pacific contributed significantly to climate evolution in the latest Cretaceous, the culmination of a period of long-term cooling. Here, we present new high-resolution late Campanian to Maastrichtian benthic and planktic foraminiferal stable isotope data and a neodymium (Nd) isotope record obtained from sedimentary ferromanganese oxide coatings of Ocean Drilling Program Hole 1210B from the tropical Pacific Ocean (Shatsky Rise). These new records resolve 13 million years in the latest Cretaceous, providing insights into changes in surface and bottom water temperatures and source regions of deep to intermediate waters covering the carbon isotope excursions of the Campanian-Maastrichtian Boundary Event (CMBE) and the Mid-Maastrichtian event (MME). Our new benthic foraminiferal d18O and Nd isotope records together with published Nd isotope data show markedly parallel trends across the studied interval over a broad range of bathyal to abyssal water depths interpreted to reflect changes in the intensity of deep-ocean circulation in the tropical Pacific. In particular, we observe a three-million-year-long period of cooler conditions in the early Maastrichtian (72.5 to 69.5 Ma) when a concomitant change toward less radiogenic seawater Nd isotope signatures probably marks a period of enhanced admixture and northward flow of deep waters with Southern Ocean provenance. We suggest this change to have been triggered by intensified formation and convection of deep waters in the high southern latitudes, a process that weakened during the MME (69.5 to 68.5 Ma). The early Maastrichtian cold interval is closely related to the negative and positive carbon isotope trends of the CMBE and MME. The millions-of-years long duration of these carbon cycle perturbations suggests a tectonic forcing of climatic cooling, possibly related to changes in ocean basin geometry and bathymetry.