Benthic foraminiferal carbon isotopic records and the development of abyssal circulation in the eastern North Atlantic.

Abstract

The evolution of Cenozoic abyssal circulation of the N Atlantic region was related to tectonic opening and subsidence of a complex of sills. We used delta 13C records of the benthic foraminifer Cibicidoides to decipher the timing of tectonically controlled changes in bottom-water circulation in the Biscay and Iberian basins. Records from Site 608 show that from approx 24-15Ma, delta 13C values in the Kings Trough area were depleted relative to W North Atlantic values and were more similar to Pacific delta 13C values. This reflects less ventilation of the Kings Trough region as compared to the well-oxygenated W North Atlantic. Comparison of Oligocene delta 13C records from Site 119 with W North Atlantic records suggests that the E basin was also relatively isolated prior to 24Ma. At approx 15Ma, delta 13C values at Site 608 attained values similar to the W North Atlantic, indicating increased E basin ventilation in the middle Miocene. This increased advection into the E basin predated a major delta 18O increase which occurred at approx 14.6Ma. Subsidence estimates of the Greenland-Scotland Ridge indicate that the deepening of the Iceland-Faeroe Ridge was coincident with the marked change in E basin deep-water ventilation.-Authors