Late Cretaceous—Paleogene paleogeography and paleocirculation: Evidence of north polar upwelling

Abstract

Quantitative determination of biogenic silica in Late Cretaceous and Paleogene deep-sea sediment cores from the central Arctic Ocean provides evidence of open-ocean polar upwelling. The timing of polar upwelling coincides with periods of a weakened meridional thermal gradient, suggesting that heat transport to the poles by oceanic circulation may have been important. The timing of biogenic silica deposition in the Arctic precedes its deposition in both the Norwegian—Greenland Sea of the North Atlantic and he Bering Sea of the North Pacific. Tectonic events may be resposnible for the timingg and sitting of sites of deposition of biogenic silica in high northern latitudes, particularly the tectonic evolution of sites of deep-water exchange between the Arctic and the world ocean. We outline three phases in the post-mid-Cretaceous history of silica deposition in high northern latitudes. During Phase I, the Arctic is a silica sink, with deep-water formation but with no deep-water outflow. The transition to Phase II is brought about by opening of the Svalabard—Greenland Strait to deep-water outflow from the Arctic to the Norwegian—Greenland Sea. The transition to Phase III is initiated by submergence of the Faroe—Iceland Ridge and deep-water outflow from the Arctic to the North Atlantic. Climatic conditions in the Arctic during Late Cretaceous and Paleogene time are predicted to have favored open-ocean upwelling due to a circulation pattern dominated by cyclonic conditions, resulting from the establisment of a semi-permanent atmospheric low over the Alpha Ridge. Bathymetry of the Alpha Ridge may have intensified paleo-upwelling.