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We present high-resolution infrared spectra of four YSOs (T Tau N, T Tau S,RNO 91, and HL Tau). The spectra exhibit narrow absorption lines of 12CO, 13CO,and C18O as well as broad emission lines of gas phase12CO. The narrowabsorption lines of CO are shown to originate from the colder circumstellargas. We find that the line of sight gas column densities resulting from the COabsorption lines are much higher than expected for the measured extinction foreach source and suggest the gas to dust ratio is measuring the dust settlingand/or grain coagulation in these extended disks. We provide a model ofturbulence, dust settling and grain growth to explain the results. Thetechniques presented here allow us to provide some observationally-motivatedbounds on accretion disk alpha in protostellar systems

Dust Stratification in Young Circumstellar Disks