Simulating marine neodymium isotope distributions using Nd v1.0 coupled to the ocean component of the FAMOUS–MOSES1 climate model: sensitivities to reversible scavenging efficiency and benthic source distributions

• Published in: Geoscientific Model Development
• Main Authors: Robinson, Suzanne, Ivanovic, Ruza F., Gregoire, Lauren J., Tindall, Julia, Flierdt, Tina, Plancherel, Yves, Pöppelmeier, Frerk, Tachikawa, Kazuyo, Valdes, Paul J.
• Format: Text
• Language: English
• Published: 2023
• Subjects: Pacific; North Atlantic
• Online Access: https://doi.org/10.5194/gmd-16-1231-2023; https://gmd.copernicus.org/articles/16/1231/2023/

The neodymium (Nd) isotopic composition of seawater is a widely used ocean circulation tracer. However, uncertainty in quantifying the global ocean Nd budget, particularly constraining elusive non-conservative processes, remains a major challenge. A substantial increase in modern seawater Nd measurements from the GEOTRACES programme, coupled with recent hypotheses that a seafloor-wide benthic Nd flux to the ocean may govern global Nd isotope distributions ( ε Nd ), presents an opportunity to develop a new scheme specifically designed to test these paradigms. Here, we present the implementation of Nd isotopes ( 143 Nd and 144 Nd) into the ocean component of the FAMOUS coupled atmosphere–ocean general circulation model (Nd v1.0), a tool which can be widely used for simulating complex feedbacks between different Earth system processes on decadal to multi-millennial timescales. Using an equilibrium pre-industrial simulation tuned to represent the large-scale Atlantic Ocean circulation, we perform a series of sensitivity tests evaluating the new Nd isotope scheme. We investigate how Nd source and sink and cycling parameters govern global marine ε Nd distributions and provide an updated compilation of 6048 Nd concentrations and 3278 ε Nd measurements to assess model performance. Our findings support the notions that reversible scavenging is a key process for enhancing the Atlantic–Pacific basinal ε Nd gradient and is capable of driving the observed increase in Nd concentration along the global circulation pathway. A benthic flux represents a major source of Nd to the deep ocean. However, model–data disparities in the North Pacific highlight that under a uniform benthic flux, the source of ε Nd from seafloor sediments is too non-radiogenic in our model to be able to accurately represent seawater measurements. Additionally, model–data mismatch in the northern North Atlantic alludes to the possibility of preferential contributions from “reactive” non-radiogenic detrital sediments. The new Nd isotope scheme forms an ...