Blue carbon sequestration dominated by dissolved organic carbon pathways for kelp forests and eelgrass meadows in Nova Scotia, Canada

Existing estimates of carbon sequestration by coastal vegetated ecosystems (e.g., kelp forests, seagrass meadows) remain highly uncertain because they utilize few measurements with high uncertainty or focus on individual stocks or fluxes. Here, we combine empirical data with modeling to generate detailed carbon budgets for kelp forests and eelgrass meadows in Nova Scotia, Canada. Our budgeting showed that the release and export of dissolved organic carbon accounts for substantially more carbon sequestered by these habitats than has been estimated globally (98.5 ± 64.6% for kelp and 84 ± 36.0% for eelgrass), suggesting this carbon pathway has been undervalued. Further, kelp forests are estimated to sequester more carbon than eelgrass by ~1.3 orders of magnitude (27 ± 19% and 12.1 ± 6.3% of annual net primary production for kelp and eelgrass) mainly due to their large habitat area, highlighting their significant but largely overlooked role in ocean carbon sequestration relative to other blue carbon ecosystems.