The NECCTON D5.2 report provides a description of the additions and improvements made to the suite of marine biogeochemical models being used in NECCTON, and their relationship to the new pelagic lower trophic level products that are being delivered. It is intended to serve as a reference for internal and external users of the products, allowing them to understand the processes that influence spatio-temporal patterns within the data, the underlying assumptions and potential sources of error. The document includes a description of each process, and its encapsulation in mathematical form. It also includes a brief description of the implementation in code, and the results of testing the new models.