This summer, Emily and I spent nearly three months sampling glacier- and snow-fed rivers draining continuous permafrost in the high Arctic Zackenberg River catchment, NE Greenland. Rivers play an important role in the long-term carbon cycle, transporting dissolved and particulate material from the chemical and physical breakdown of rocks on the continents to the oceans. These ‘weathering’ processes can both release and remove carbon dioxide (CO₂) from the atmosphere, and we don’t know which of these processes dominates overall in Arctic river systems. This has huge implications for understanding whether Arctic rivers are acting as a source or sink for atmospheric CO₂, and therefore, how weathering in the Arctic impacts the long-term carbon cycle and climate.