Eroding Arctic coasts

The Arctic is experiencing rapid warming, nearly four times faster than the global average. This region is known for its permafrost, ground that has remained frozen or stayed at 0°C for at least two consecutive years and stores vast amounts of organic carbon. In fact, permafrost contains nearly twice as much carbon as is currently present in the atmosphere. However, as temperatures rise and the ground begins to thaw, this once-trapped carbon is released into the environment. One of the most visible and impactful consequences of rapid thaw is coastal erosion, which transports organic material from land into the Arctic Ocean. In this study, we investigate how coastal erosion contributes to the release of organic carbon and what happens to it once it enters the marine system. Understanding the fate of this carbon, whether it becomes buried in sediments or breaks down during transport and becomes a greenhouse gas like CO₂, is critical for improving our understanding of permafrost carbon feedback loops. To study these processes, we used a method called hydrodynamic fractionation, which allows us to separate and track different carbon fractions based on their size, density, and interaction with minerals. Using geochemical analysis, we further determined the age (Δ¹⁴C), composition (δ¹³C), and reactivity of the different fractions of organic carbon. This approach helps us understand how carbon moves through the system, where it is resuspended, degraded, or deposited, and which fractions are most likely to contribute to CO₂ emissions. One of our key findings is that the nearshore zone (waters less than 5 meters deep), located just off the eroding coastline, is critically undersampled. Only 6% of sediment samples in the Arctic basin are collected in this shallow zone. Despite covering just a small portion of the Arctic Ocean, the nearshore zone plays a key role in carbon cycling. Waves and currents frequently resuspend freshly eroded material, exposing it to oxygen and microbes that accelerate degradation. Much of this material consists of unprotected vascular plant debris, which holds organic carbon that is particularly prone to breaking down. This means the nearshore is not just a transition zone, it is a hotspot for carbon degradation. However, logistical challenges make it difficult to sample these shallow, remote waters, resulting in a major research gap. Beyond carbon, this research has significant implications for the people who live in the Arctic. Indigenous communities, such as those in Tuktoyaktuk in Canada’s Northwest Territories, depend on the stability of permafrost for homes, food storage, and cultural practices. As the ground thaws, coastlines collapse, ecosystems shift, and traditional travel and hunting routes become increasingly dangerous. As the Arctic climate continues to change, both carbon stocks and communities are at risk. This study underscores the need to more closely monitor vulnerable coastal zones, improve our climate feedback models, and integrate local and Indigenous knowledge to build a more complete understanding of a rapidly changing Arctic.

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