Yedema et al. used multiple biomarkers and palynological proxies to track the fate of plant-derived, soil-microibal, fluvial, and marine-produced organic matter in the coastal sediments of the northern Gulf of Mexico. The key findings show plant-derived materials reaching the deepest waters in contrast to fluvial organic matter confined to the proximity of the river mouth. This source-specific difference in the coastal distribution and storage of organic matter can greatly contribute to elucidating the role of terrestrial organic matter in coastal carbon sequestration.