Modeling Neodymium Isotopes in the Ocean Component of the Community Earth System Model (CESM1).

Neodymium (Nd) isotopic composition (εNd) is an important tracer for water mass mixing and the reconstruction of past ocean circulation. To allow for a direct model‐data comparison, we have implemented Nd isotopes in the ocean component of the Community Earth System Model (CESM1.3). The model is able to capture the major features of the observed modern distribution of both εNd and Nd concentrations. Our model provides a useful tool for the interpretation of εNd reconstructions. For example, we show that in an idealized North Atlantic freshwater hosing experiment, εNd changes in the Atlantic are documenting primarily the changes in water mass mixing and are hardly affected by the concomitant and large changes in the marine biological productivity and organic matter fluxes. However, the hosing experiment also shows that the end‐member changes due to the change of ocean circulation can influence the interpretation of εNd in the Atlantic, depending on the location. The implementation of Nd, together with other existing tracers, such as δ18O, 231Pa/230Th, δ13C, and radiocarbon in the same model, can improve our understanding of past ocean circulation significantly. Plain Language Summary: The Climate model is an important tool to study past climate. However, previous model‐data comparison suffers from indirect comparison since reconstructions measures proxy records and climate model simulate physical variables, both of which have uncertainties and it is hard to address the model data discrepancies. To meet this challenge, we implement the Nd isotopes, which is more and more used in paleoceanography, in the ocean component of the Community Earth System Model (CESM). Our model is able to simulate εNd in good agreement with observations. With other isotopes, such as δ18O, 231Pa/230Th, δ13C, and radiocarbon in the same model, this isotope‐enabled CESM provides a powerful tool to improve the understanding of past ocean circulation changes. Furthermore, the hosing experiment suggests that the interpretation of εNd changes in the Atlantic as changes in the water mass mixing can be complicated by the changes in the end‐member values in some locations. Key Points: Nd isotopes are implemented in the CESM1, which simulate the Nd concentration and εNd in reasonable agreement with observationsIn idealized water hosing experiment, εNd changes in the Atlantic mainly reflect changes in the mixing between different water massesEnd‐member changes due to the change of ocean circulation can influence the interpretation of εNd in some locations [ABSTRACT FROM AUTHOR]