The polar oceans have already experienced significant ecosystem shifts associated with sea ice retreat. Earth system models suggest that major changes in marine ecosystems and biogeochemistry will keep on going through the 21st century. However, future projections of the polar oceans are subject to some of the largest uncertainties. Among the sources of uncertainty is the role of sea ice: Earth system models consider sea ice as biologically inert, while observations indicate active biogeochemistry in sea ice. Hence, developing a realistic sea ice biogechemistry model component seems necessary. The fact that sea ice is so prone to microbial life is due to the fact that compared to freshwater ice, sea ice is highly porous. Practically, sea ice can be viewed as a matrix of solid ice with liquid inclusions of brine. Depending on permeability, brine inclusions are connected or not with the underlying ocean. The brine network is ventilated by brine drainage mechanisms, supplying or flushing out nutrients. In this presentation, based on observations and models, I will contextualize, explain and show how to model one fundamental aspect of biogeochemistry in sea ice, namely how biogeochemistry in sea ice is coupled with liquid brine dynamics.