A model-based feasibility study

Over the past decade, records of the seawater neodymium isotopic composition (εNd) have become a widely used proxy to reconstruct changes in ocean circulation. Our study investigates the transient response of εNd to large-scale ocean circulation changes using an Earth system model of intermediate complexity. It is shown that a weakening of the North Atlantic Deep Water formation results in positive εNd anomalies in the Atlantic and the Pacific below 1000 m water depth whereas variations in Antarctic Bottom Water production generate a Pacific-Atlantic dipole pattern of deep ocean εNd changes. Further experiments explore which ocean regions are suitable to record the temporal evolution of the overturning in the North Atlantic and the Southern Ocean by means of εNd data. High local correlations occur between simulated Southern Ocean overturning changes and simulated εNd anomalies in the deep North Pacific and almost globally for simulated North Atlantic overturning changes, respectively, clearly indicating the strong potential of εNd to work as a proxy of past ocean circulation changes. Finally, the compromising effects of simultaneously occurring anomalies in the North Atlantic and the Southern Ocean overturning cells on reconstructions of past ocean circulation changes are identified. Combining our model simulations with currently available core data, our study demonstrates that changes in εNd documented in numerous Atlantic paleorecords clearly support the notion of a strengthening in the Atlantic Meridional Overturning Circulation over the course of Termination 1.

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