Ocean circulation reconstructions from ε_Nd: A model-based feasibility study

Friedrich, T., Timmermann, A., Stichel, T. and Pahnke, K. (2014) Ocean circulation reconstructions from ε_Nd: A model-based feasibility study. Paleoceanography, 29 (11), 1003-1023. (doi:10.1002/2014PA002658).

Abstract

Over the past decade, records of the seawater neodymium isotopic composition (ε_Nd) have become a widely used proxy to reconstruct changes in ocean circulation. Our study investigates the transient response of ε_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 formation results in positive ε_Nd 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 ε_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 ε_Nd data. High local correlations occur between simulated Southern Ocean overturning changes and simulated ε_Nd anomalies in the deep North Pacific and almost globally for simulated North Atlantic overturning changes, respectively, clearly indicating the strong potential of ε_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 ε_Nd 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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