Supplementary: Simulating neodymium isotopes in the ocean component of the FAMOUS general circulation model (XPDAA): sensitivities to reversible scavenging efficiency and benthic source distributions

• Main Authors: Robinson, Suzanne, Ivanovic, Ruza, Gregoire, Lauren, Tindall, Julia, van de Flierdt, Tina, Plancherel, Yves, Pöppelmeier, Frerk, Tachikawa, Kazuyo, Valdes, Paul
• Format: Dataset
• Language: English
• Published: University of Leeds 2022
• Subjects: F670 - Geochemistry; F731 - Ocean circulation; F764 - Climate & climate change; Pacific; North Atlantic
• Online Access: https://archive.researchdata.leeds.ac.uk/979/; https://archive.researchdata.leeds.ac.uk/979/1/README.txt; https://archive.researchdata.leeds.ac.uk/979/2/code_and_inputs.zip; https://archive.researchdata.leeds.ac.uk/979/3/model_output.zip

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 (εNd) presents an opportunity to develop a new scheme specifically designed to test these paradigms. Here, we present the implementation of Nd isotopes (143Nd and 144Nd) into the ocean component of the FAMOUS coupled atmosphere-ocean general circulation model, 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 largescale Atlantic Ocean circulation, we perform a series of sensitivity tests evaluating the new Nd isotope scheme. We investigate how Nd source/sink and cycling parameters govern global marine εNd distributions, and provide an updated compilation of 6,048 Nd concentration and 3,278 εNd measurements to assess model performance. Our findings support the notions that reversible scavenging is a key process for enhancing the Atlantic-Pacific basinal εNd 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 the source of εNd from seafloor sediment is too unradiogenic in our model with a constant benthic flux. Additionally, model-data mismatch in the northern North Atlantic suggests a missing source of Nd that is much more unradiogenic than the bulk sediment, alluding to the possibility of preferential contributions from ‘reactive’ detrital sediments under a benthic flux driven model of marine Nd ...