The Canadian Beaufort Sea is characterized by predominantly permafrost coastlines that are particularly vulnerable to coastal erosion due to high amounts of unconsolidated sediments. Additionally, the Mackenzie River transports suspended sediments and discharges large amounts of remobilized carbon nearshore. The rate at which marginal coasts erode and sediment accumulates is expected to increase with rising sea level and enhanced fluvial sediment transport. To understand how these coastal systems develop over time it is essential to investigate their past evolution. Here, a 9m long sediment core from Tuktoyaktuk Harbor was investigated to resolve past variability in sediment and terrestrial carbon delivery to the nearshore environment. The core is constrained by an age model spanning the last 10,000 years. Our results show that the site initially hosted a freshwater fen in the Early Holocene before transitioning into a thermokarst lake during the mid-Holocene. Initial marine inundation occurred at 4315±514 cal yr BP. Continued transgression transformed the site into a lagoon with strongly anoxic bottom waters. Reduced anoxia over time led to the establishment of a brackish lagoon. Over the last millennium deposits exhibit a notable increase in petrogenic carbon delivery, indicating enhanced erosion of ancient carbon stocks within the Mackenzie River watershed.