Standardising research on marine biological carbon pathways required to estimate sequestration at Polar and sub-Polar latitudes

Marine biological ('blue') carbon pathways are crucial components of the global carbon budget due to the ecosystem services they provide through the fixation of CO2 from the atmosphere. CO2 is removed from biosphere through long-term sequestration into seafloor sediments, removing it from the carbon cycle. Coincident with marine ice loss, little studied negative (mitigating) feedbacks to climate change are emerging in polar waters, which is important to quantify and comprehend. Understanding the mechanisms driving these pathways, that could lead to change, is a massive task and to ensure studies are comparable requires standardisation and prioritisation of future research. The expertise of scientists within the EU grant, Coastal ecosystem carbon balance in times of rapid glacier melt (CoastCarb), identified the 23 most important high latitude pathways through a modified Delphi scoring system. Metrics were selected as priorities for future research and for syntheses across broader geographic regions. The metrics with the highest importance scores also scored as the metrics that could be most readily standardised in the next five years. This review provides a definition and description of how each metric is measured, including its central role to blue carbon pathways. It also provides recommendations for standardisation, emphasising the requirement for modelling studies to scale from geographically limited regions where high-resolution data is available. Where methods cannot be standardised, cross calibration between methods is required to ensure reproducibility. An increasing use of remote sensing and innovative technologies will be necessary to scale measurements across this vast and remote region.