Changes in North Atlantic circulation at the end of the Cretaceous greenhouse interval

The mechanics of ocean circulation during the Late Cretaceous greenhouse interval remain contested(1-6), with the role of North Atlantic Deep Water in ocean circulation particularly debated: the relative warming of the North Atlantic during the termination of the greenhouse interval has been attributed to heat piracy from North Atlantic Deep Water formation(5,6), but the sources of Cretaceous deep water have been difficult to resolve. Nd isotopes as captured by seafloor sediments and expressed as epsilon(Nd(t)) reflect the region in which the water mass was formed. Here we present epsilon(Nd(t)) measurements from Cretaceous-to Palaeogene-aged sediments from four cores in the tropical North Atlantic. Before 69 Myr ago, we find extremely low epsilon(Nd(t)) values of about -16, consistent with the presence of a warm, saline deep water mass formed in the low latitudes(7,8). By 62 Myr ago, epsilon(Nd(t)) values had risen to -11, similar to values reported from the northern North Atlantic over the past 65 million years, but lower than most contemporaneous values in the South Atlantic(9) and Pacific oceans(7,10). We therefore suggest that the epsilon(Nd(t)) shift reflects the increasing influence of a northern-sourced water mass at this site, indicating the onset or intensification of deep-or intermediate-water formation in the North Atlantic 69 Myr ago. Our findings support the heat piracy model and imply that circulation patterns during the greenhouse interval were different from those of the subsequent relatively temperate interval.