Ocean circulation reconstructions from eps(Nd): A model-based feasibility study

Over the past decade, records of the seawater neodymium isotopic composition (eps(Nd)) have become a widely-used proxy to reconstruct changes in ocean circulation. Our study investigates the transient response of eps(Nd) 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 (NADW) formation results in positive eps(Nd) anomalies in the Atlantic and the Pacific below 1000 m water depth whereas variations in Antarctic Bottom Water (AABW) production generate a Pacific-Atlantic dipole pattern of deep ocean eps(Nd) 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 eps(Nd) data. High local correlations occur between simulated Southern Ocean overturning changes and simulated eps(Nd) anomalies in the deep North Pacific and almost globally for simulated North Atlantic overturning changes respectively; clearly indicating the strong potential of eps(Nd) 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 eps(Nd) documented in numerous Atlantic paleo-records clearly support the notion of a strengthening in the Atlantic Meridional Overturning Circulation over the course of Termination 1.

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