Permafrost thaw is driving the release of previously sequestered carbon. While much focus has been on vertical carbon fluxes to the atmosphere, carbon transported by surface water and groundwater in thawing hillslopes, termed lateral carbon fluxes, remain unconstrained and represent a significant portion of “missing” carbon in the Arctic. In this study, we monitored hydrogeochemical dynamics at two headwater catchments drained by water tracks on the North Slope of Alaska. Dissolved and particulate organic carbon (DOC/POC) and discharge were monitored at 15-min intervals through the 2024 field season and concentration–discharge (C-Q) responses were quantified at seasonal and storm scales. Results show drastically different C-Q responses between catchments based on landscape and hydrological controls. One catchment showed DOC enrichment (transport-limited) with more total DOC export and lower POC fluxes. The second catchment displayed DOC dilution (source-limited), less total DOC export, but higher POC fluxes. Mixing models were employed to constrain the flow regimes governing C-Q dynamics. Results suggest two distinct hillslope hydrological responses to storm events: (1) hillslopes that mobilize older water exhibit a flushing response, increasing DOC concentrations with discharge, but reducing POC export due to deeper flow paths; and (2) hillslopes that rapidly route event water with limited mixing show a dilution response, reducing DOC concentrations with discharge, but enhancing POC export through increased near-surface and preferential pathways. This work provides a process-based framework for understanding of the fate of permafrost carbon, including critical constraints on how much carbon is mineralized within hillslopes versus laterally exported to surface waters.