Evidence for Oligocene–Middle Miocene abyssal circulation changes in the western North Atlantic

Abstract

Previous studies of benthic foraminiferal isotopic composition have demonstrated that a latest Eocene–earliest Oligocene benthic foraminiferal δ¹⁸O increase occurred in the Pacific, Southern and Atlantic Oceans^1–9. A Middle Miocene δ¹⁸O increase has been noted in the Pacific, Southern and South Atlantic Oceans^{1–3,7,10,11} and tentatively identified in the North Atlantic^12,13. Due to the incomplete nature of the North Atlantic stratigraphical record^14,15, however, the Oligocene to Middle Miocene isotopic record of this ocean is poorly understood. In the modern ocean, the North Atlantic and its marginal seas has a critical role in abyssal circulation, influencing deep- and bottom-water hydrography as far away as the North Pacific^16–18. We now report oxygen isotope measurements on Oligocene to Middle Miocene (12–36 Myr BP) benthic foraminifera in the western North Atlantic which show two periods of enriched ¹⁸O values: early Oligocene and early Middle Miocene. These enriched intervals are interpreted as resulting, in part, from the build-up of continental ice sheets. The Oligocene to Middle Miocene δ¹³C record shows three cycles of enrichment and depletion of large enough magnitude to be useful for time–Stratigraphical correlations. Within the biostratigraphical age resolution, δ¹⁸O and δ¹³C records correlate with records from other oceans, helping to establish a useful Tertiary isotopic stratigraphy. An Atlantic–Pacific δ¹³C contrast of 0.3–0.9‰ during the latest Oligocene to Middle Miocene (12–26 Myr BP) indicates North Atlantic deep and bottom-water production analogous to modern North Atlantic deep water (NADW).