MARBL is a modular biogeochemical modeling suite for next-generation ocean models. This project is developing an Oceanic General Circulation Model (OGCM) independent library for the simulation of marine ecosystems and biogeochemical cycles. The objective is to produce a flexible ocean biogeochemical modeling (OBM) tool that will facilitate research on a range of scientific questions. It will enable climate-timescale high-resolution simulations and permit tailoring model configurations aimed at very different research questions within a common code base, such as climate impacts on fisheries versus carbon-climate feedbacks. Coupled with the MPAS-O ability for local grid refinement, the OBM will be able to target regional systems with intensive observations, leading to robust constraints on model skill. The code base will be extensible from a scientific point of view, since modularization will facilitate revising the treatment of key processes. In addition, the code will naturally accommodate adding optional tracers systems for unique research questions, such as comparison to paleoceanographic observations. The OBM tool that this project develops will be freely available, thereby facilitating community participation and leveraging intellectual contributions from a broad array of researchers.