05 April 2019

Neodymium Isotopes in the Ocean Model Traces Water Mass Mixing

Neodymium-enabled ocean model allows direct comparison of the model simulated neodymium to ocean proxy records.

Science

Neodymium isotopic ratio in the Atlantic can reflect changes in the mixing between different water masses. After our implementation of this important tracer, we are able to simulation this tracer directly in the state-of-the-art climate model and compare with proxy records in the deep ocean. This neodymium-enabled climate model will help us to understand how the ocean evolved in the past and how it will change in the future.

Impact

Nd isotopes are implemented in the CESM, which simulate the Nd concentration and εNd in reasonable agreement with observations. With other isotopes, such as oxygen isotopes (δ18O), the marine sedimentary 231Pa/230Th ratio, can carbon isotopes (δ13C and radiocarbon) in the same model, this isotope‐enabled CESM provides a powerful tool to improve the understanding of past ocean circulation changes.

Summary

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.

Contact
Jiaxu Zhang
Los Alamos National Laboratory
Publications
Gu, S, Z Liu, A Jahn, J Rempfer, J Zhang, and F Joos.  2019.  "Modeling Neodymium Isotopes in the Ocean Component of the Community Earth System Model (CESM1)."  Journal of Advances in Modeling Earth Systems 11(3): 624 - 640.  https://doi.org/10.1029/2018MS001538.