Precession‐Related Variability in North Pacific Deep Water Formation in the Early Eocene: Insights From cGENIE Simulations

Abstract

Past warmhouse climates differed from the modern ocean circulation regime, with deep‐water formation occurring in regions that are inactive today. Evidence suggests that the North Pacific may have been one such region. The early Eocene, characterized by elevated greenhouse gas concentrations and orbitally paced carbon cycle perturbations, provides a test case for exploring alternative modes of deep‐ocean ventilation. However, the extent to which astronomical parameters and orbital configurations modulated deep‐water formation in the North Pacific remains poorly understood. Here, we use the intermediate‐complexity Earth system model cGENIE to isolate the sensitivity of early Eocene ocean circulation to astronomical forcing. The simulations reveal that the eccentricity‐modulated climatic precession exerts a substantially stronger influence on ocean circulation than either eccentricity or obliquity, with the most pronounced response occurring in the North Pacific. The precession configuration that is associated with enhanced Northern Hemisphere seasonality (Pmin) produces deeper winter mixed layers, stronger vertical exchange, and more favorable conditions for North Pacific deep‐water formation in the model. The opposite configuration (Pmax) results in shallower winter mixing and favors the formation of intermediate rather than deep waters. These results suggest that, under warmhouse boundary conditions, seasonal insolation changes associated with eccentricity‐modulated precession could modify the depth and strength of overturning circulation. Our simulations may provide a mechanistic framework for interpreting orbital‐scale variability in ocean ventilation, carbon cycling, and climate during the early Eocene.