Final answer:
The most important transport mechanism for weathered material in subarctic zones is mass wasting, driven by gravity and aided by freeze-thaw cycles.
Step-by-step explanation:
The single most important mechanism of transport for weathered overburden in subarctic zones is mass wasting. Mass wasting refers to the downhill movement of soil and rock material due to gravity. In subarctic regions, this process is largely facilitated by the freeze-thaw cycles that cause frost wedging and further contribute to the breakage and movement of material. Compared to other mechanisms listed such as frost wedging, hydrolysis, exfoliation, and oxidation, mass wasting is the primary mode of transport for the fragmented material over the surface in these cold climate zones.