Shan Liu

The Arctic Ocean plays a pivotal role in global climate, yet its circulation under greenhouse conditions remains poorly constrained. Seismic, sedimentological, and drilling evidence from the Chukchi Shelf reveals large contourite drifts and bathyal carbonate mounds dated to the Campanian to Maastrichtian [~80 to 66 million years ago (Ma)], indicating persistent bottom currents and high productivity. These features point to the presence of a regionally sourced Boreal deep-water mass, likely driven by seasonal sea-ice formation and brine rejection. Bathyal carbonate mound development was sustained by tidal mixing, localized upwelling, and well-oxygenated conditions following Oceanic Anoxic Event 3. This vigorous circulation system collapsed at the Cretaceous-to-Paleogene boundary, coinciding with closure of the Western Interior Seaway and reorganization of global circulation. Our findings challenge the prevailing view of a sluggish, surface-dominated Late Cretaceous Arctic, demonstrating instead that it supported deep-water formation and localized carbonate factories, highlighting its key role in high-latitude climate dynamics under greenhouse conditions.

Oceanic gateways play a crucial role in controlling global ocean circulation. However, gateway effects on low-latitude deep-water circulation are poorly understood. The South China Sea, located in the western Pacific, was influenced by changes in the equatorial and low-latitude gateways, which recorded significant oceanographic variations since the Oligocene. Here, we identify contourite features in the deep South China Sea from seismic data and drill cores from Ocean Drilling Program Leg 184 and International Ocean Discovery Program Expeditions 349 and 367/368, as evidence for the influence of Circumpolar Deep Water originating from the eastern Indian Ocean until ca. 10 Ma. Final closure of the deep Indonesian Gateway at ca. 10 Ma caused disruption of the deep-water connection between the Pacific and Indian Oceans and a reorganization of global deep-water circulation. These changes in gateway tectonics may significantly contribute to the Middle to Late Miocene global climate and oceanic conditions.

The Cretaceous ocean was significantly different from its modern counterpart due to its ice-free condition. Deep waters were primarily sourced by evaporation at the ocean surface, although their circulation pattern and bottom-current dynamics have been largely unknown. Here we present a study of deeply buried contourite drifts in the southern proto–Bay of Biscay to unravel the circulation pattern of the mid- and Late Cretaceous deep waters across the northeast Atlantic. The generation of plastered drifts (120 Ma to 100–90 Ma) and a mounded drift (100–90 Ma to 65 Ma) suggests that a significant change in deep-water source regions from the Tethys to the high-latitude region occurred at ca. 100–90 Ma. These contourite drifts were buried after ca. 65 Ma when the Cretaceous ocean circulation transitioned to the Cenozoic style in the northeast Atlantic. Tectonic configurations of the Pyrenean and the Equatorial Atlantic gateways were moreover tied to significant changes in northeast Atlantic deep-water circulation at ca. 100–90 and ca. 65 Ma. Northeastern Spain and France might be potential sites for the detection of Late Cretaceous contourite outcrops. These outcrops could have fundamental implications for the sedimentary facies and sequence model of contourites as well as shed light on the paleoceanography and paleoclimate of Cretaceous Earth.