Modeling Ocean Distributions of Neodymium Isotopes Using a Bottom-up Approach

The isotopic composition of neodymium (𝜀Nd) is used as a tracer for modern and past global Meridional Overturning Circulation (MOC) changes. Previous ocean models of 𝜀Nd have focused on a top-down approach using an equilibrium scavenging coefficient. This approach assumes that Nd is supplied to the ocean primarily through terrestrial sources at the surface, and that reversible scavenging on particles leads to downward redistribution of Nd in the water column. Here, we explore a different framework based on the bottom-up approach and irreversible scavenging using a three-dimensional global general circulation numerical model. A deliberately simple (3 parameter) model is constructed and explored with sensitivity experiments to test assumptions about the isotopic composition and the depth-dependency of the benthic flux, which is considered the sole source of Nd to the water column. The 𝜀Nd signature of the benthic flux is estimated from a linear relation 𝜀Nd PW =m×𝜀Nd Det + b, between porewater (𝜀NdPW) and core-top detrital 𝜀Nd (𝜀NdDet). Models with 1.5