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High latitude warming and permafrost thaw will expose vast stores of deep soil organic carbon (SOC) to decomposition. Thaw also changes water movement causing either wetter or drier soil. The fate of deep SOC under different thaw and moisture conditions is unclear. We measured weekly growing‐season δ¹³C of ecosystem respiration (Recoδ¹³C) across thaw and moisture conditions (Shallow‐Dry; Deep‐Dry; Deep‐Wet) in a soil warming manipulation. Deep SOC loss was inferred from known δ¹³C signatures of plant shoot, root, surface soil, and deep soil respiration. In addition, a 2‐year‐old vegetation removal treatment (No Veg) was used to isolate surface and deep SOC decomposition contributions to Reco. In No Veg, seasonal Recoδ¹³C indicated that deep SOC loss increased as the soil column thawed, while in vegetated areas, root contributions appeared to dominate Reco. The Recoδ¹³C differences …