Review of organic carbon source and burial in polar fjords

Fjords are an important interface between the open ocean and terrestrial ecosystems. In the context of global climate change, the biogeochemical processes in fjords are undergoing dramatic changes. The special topography and biogeochemical properties of fjord make it an important ecosystem for organic carbon (OC) burial and storage. Studies have shown that the average OC accumulation rate in the global fjords is as high as 54 gC·m⁻²·a⁻¹, and the OC burial amount is 18×10¹² gC·a⁻¹, taking about 11% of the annual global marine OC burial and showing a great carbon storage potential. The input, composition, and accumulation or burial of sedimentary OC in polar fjords are different from those in temperate fjords due to glaciation. There are spatial differences in the source, composition, accumulation, and burial rate of sedimentary OC within and between polar fjords. Within a fjord, there is a gradient change from the front of the fjord to the mouth of the fjord; and between fjords, those with glaciers have higher carbon accumulation rates than those without glaciers. In addition, the composition of sedimentary OC varies due to the influence of different freshwater and seawater inputs. Clarifying the sources of fjord sediment OC is crucial to understanding fjord OC burial. Quantitative estimation of OC from different sources can be achieved by measuring total OC and radiocarbon isotopes of bulk organic matter and the technology of Compound - Specific Radiocarbon Analysis (CSRA). The accumulation or burial of OC in polar fjords shows different characteristics due to the rapid retreating of glaciers by global warming. Global warming is causing rapid glaciers to melt, causing polar fjords to exhibit different organic carbon accumulation or burial characteristics. In the global carbon cycle, it is increasingly important to study whether the ability of polar fjords to capture and bury OC can adapt to global climate change.