87/86Sr 9 phytoplankton, and the nature of the Late Cretaceous and Early Cenozoic Arctic Ocean

The Arctic Ocean’s link to the lower latitude World Ocean during the Late Cretaceous and early Cenozoic is puzzling. The tectonic development of the Arctic Ocean evidently included termination of the Pacific-Arctic connection late in the Cretaceous, and the Atlantic link was not significant until at least the Eocene. Yet, during the Late Cretaceous Arctic Ocean mollusks indicate that there was no more than partial restriction, and Late Cretaceous and middle Eocene phytoplankton species are the same in both the Arctic and World Ocean. Sr isotope ratios of fish associated with the phytoplankton are higher than that accepted as the World Ocean’s ratios for any time during this interval, yet these high ratios do not indicate an isolated Arctic Basin. The Arctic was linked with the World Ocean and the best evidence for this is the phytoplankton similarity, but the location of the marine connection remains enigmatic. 1