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Wildfires have increased in California in recent decades, linked to rising temperatures coinciding with high offshore winds and later onsets of the rainy season (Goss et al., 2020). Extreme fire-inducing conditions in late 2017 led the 2017-2018 Thomas Fire to become the largest wildfire in California's history at the time (Cal Fire, 2018). The Thomas Fire began on December 4, 2017 when two separate fires ignited south of Thomas Aquinas College in Ventura County. Several factors including dry vegetation, unusually strong Santa Ana winds, and low humidity in the winter of 2017 contributed to the spread of the fire. In

Abstract. Spatially distant sources of neodymium (Nd) to the ocean that carry different isotopic signatures (εNd) have been shown to trace out major water masses and have thus been extensively used to study large-scale features of the ocean circulation both past and current. While the global marine Nd cycle is qualitatively well understood, a complete quantitative determination of all its components and mechanisms, such as the magnitude of its sources and the paradoxical conservative behavior of εNd, remains elusive. To make sense of the increasing collection of observational Nd and εNd data, in this model description paper we present and describe the Global Neodymium Ocean Model (GNOM) v1.0, the first inverse model of the global marine biogeochemical cycle of Nd. The GNOM is embedded in a data-constrained steady-state circulation that affords spectacular computational efficiency, which we leverage to perform systematic objective optimization, allowing us to make preliminary estimates of biogeochemical parameters. Owing to its matrix representation, the GNOM model is additionally amenable to novel diagnostics that allow us to investigate open questions about the Nd cycle with unprecedented accuracy. This model is open-source and freely accessible, is written in Julia, and its code is easily understandable and modifiable for further community developments, refinements, and experiments.