Seagrass meadows are able to store significant amounts of organic carbon in their underlying sediment but global estimates are uncertain partly due to spatiotemporal heterogeneity between areas and species. In order to provide robust estimates, there is a need to better understand the fate of, and mechanisms behind, organic carbon storage. In this observational study, we analyse a suite of biotic and abiotic parameters in sediment cores from 47 different eelgrass (Zostera marina) beds spanning the distributional range of the Northern Hemisphere. Depth profiles revealed three patterns of vertical distribution where POC either increased, decreased, or showed no distinct pattern with sediment depth. These categories exhibited distinct profiles of δ13C and C:N ratios, where high POC profiles had a proportionally larger storage of eelgrass-derived material whereas low POC profiles were dominated by phytoplanktonic and macroalgal material. However, high POC did not always translate into high carbon density. Along with better constrained sedimentation rates, these results can ultimately contribute to our understanding of carbon content in seagrass beds.

2019