Upper Ocean Instability in the Subpolar North Atlantic and Its Implications for Deep Water Formation During Interglacials

Abstract In this multiproxy study, we used new isotopic data on planktonic foraminifera to highlight the strong instability that characterized surface conditions in the Iceland Basin during Marine Isotope Stage 11 (MIS 11). We produced new oxygen isotope data on the planktonic species Neogloboquadrina incompta and Turborotalita quinqueloba , foraminifera‐bound nitrogen isotope data on N. incompta , and calcareous nannofossil data at coring site IODP Site U1314. The multiproxy record displays two distinct upper ocean regimes: a relatively stable pre‐climate optimum and an unstable post‐climate optimum with high amplitude variations in nutrient utilization and seasonality proxies, and strong enrichment in oxygen isotopes suggesting colder and/or saltier upper waters. The latter regime was concomitant with a resurgence in ice‐rafted debris. Interestingly, this surface instability is not observed in cores from sites affected by the North Atlantic Current. Moreover, deep water ventilation is reconstructed to decrease throughout the eastern North Atlantic, while remaining rather constant in the Labrador Sea. The evidence presented here indicates that deep‐water formation was unstable throughout MIS 11, and that peak periods of deep‐water formation varied across high latitude North Atlantic basins, depending on the prevailing surface conditions in each region. These findings suggest that reconstructing deep‐water formation and ventilation require a comprehensive approach that accounts for the interconnectivity between different components of the overturning circulation system.