Abstract: We collected water from river depth-profiles during the peak freshets in June 2017, 2018 and 2019. Sampling locations are situated in the northern Mackenzie River basin: Mackenzie River in the delta, the Mackenzie River at Tsiigehtchic, the Arctic Red River at Tsiigehtchic and the Peel River at Fort McPherson. Depth-profiles were retrieved using a horizontally-mounted ~5.1 L Niskin bottle. The collected water was transferred to a sterilized plastic bag and subsequently filtered through 0.22 um polyethersulfone filters. This data set comprises concentration analyses of major dissolved ions, particulate and dissolved organic carbon. Furthermore, we provide radiocarbon measurements of particulate and dissolved organic carbon. We link carbon and major ion measurements to investigate changes of riverine chemistry in the Arctic Mackenzie River in response to continued climate warming. Other Description: Schwab, M. S., Hilton, R. G., Raymond, P. A., Haghipour, N., Amos, E., Tank, S. E., Holmes, R. M., Tipper, E. T. and Eglinton, T. I. (2020). An abrupt aging of dissolved organic carbon in large Arctic rivers. Geophysical Research Letters, 47, e2020GL088823.