Step-heating analyses for Mid-Atlantic Ridge glass samples show that maximum Ar-40/Ar-36 values correlate with Pb-206.207.208/Pb-204. These correlations hold for the whole Atlantic Ocean and therefore are unlikely to result from shallow-level contamination processes. Instead, they are taken as mixing hyperbolae between the degassed-depleted upper mantle and a recycled component characterized by high Pb-206/Pb-204 ratios (19 to 21) and Low Ar-40/Ar-36 ratios (300 to 1000). These relations imply that argon may also be a tracer of mantle recycling.