Biogeochemical processes associated with sea ice are still inadequately described and poorly represented in models, making it difficult to properly quantify the impacts of climate change in polar regions. Within the framework of the international Scientific Committee of Ocean Research (SCOR) working group 140, BEPSII, a community of sea-ice biogeochemical scientists established guidelines for the measurement of biogeochemical processes in sea ice, collated observed data, synthesized knowledge of sea-ice biogeochemical processes, and identified the feedbacks between biogeochemical and physical processes at the terrestrial-ocean-ice-snow-atmosphere interfaces and within the sea-ice matrix. Many of these results are presented in Elementa's Special Feature on BEPSII. By bringing together experimentalists and modelers, major improvements of sea-ice biochemistry models have been achieved which are anticipated to affect models on micro-to global scales. However, large gaps still exist in our understanding of detailed biogeochemical processes in sea ice, their seasonal evolution and their interactions with surrounding environments. The BEPSII community recommends continued focus on the development of reproducible methods and techniques for reliable inter-study comparisons, to enhance our understanding in areas where gaps have been identified via coordinated process studies combining modeling tools, laboratory experiments and field studies, and on the use of such studies to develop conceptual models helping us to understand the overall system.