468 F. S. Chapin III et al. 



TABLE 12-4 Barrow Carbon Budget Calculated by Three Methods 



Method 



Compartment Aerodynamic* Turfchambert 



KOH absorption** 



Total C fixed GCt/' =210 PM+P/V„ + /?r ' =202 PN,+PN» + R,+R» = 1U 



Ecosystem respiration R, = \10 Rs + Rt' + Ro' = »2 Rs' +Rv+R» + Ro' = \55 



Net ecosystem C gain C= 40 C=120 C= 59 



Subcompartments of 

 ecosystem respiration 



Note: All values are direct measurements unless indicated as calculated by prime notation. 

 Fluxes given as g C m'^ yr"'. 



GCU= gross community CO? uptake 

 Rt= total dark respiration above 



ground 

 Rb = total carbon efflux from eco- 

 system in dark 

 Rd = decomposer plus saprovore 

 respiration 



PNv and PN^ = net photosynthesis, vas- 

 cular and nonvascular, 

 respectively 

 Rv and /?M = dark respiration, above- 

 ground vascular and 

 moss, respectively 

 ^B = belowground vascular 



respiration 

 C = net carbon flux from 

 atmosphere 



*Coyne and Kelley (1975). 



t PNy (Tieszen 1978b); PN» (Oechel and Sveinbjornsson 1978); /?«, {Rg + Ro), and C 

 (Billings et al. 1978). 

 **PNv and PN^, (as above); R, (Tieszen 1978b); R^ (Oechel and Sveinbjornsson 1978), 

 calculated by extrapolating photosynthesis/light curves to light intensity; Ru (field) 

 (Benoit pers. comm.); Rg ' (Miller 1979) calculated from theoretical respiration costs of 

 growth and maintenance. _^_^_ 



{PNv + PN^)-iRB + Ro + RH + Rc) = 173-53 = 120 g C m-^ 



Terms are defined in Figure 12-1. 



With a carbon budget constructed for only one year, it is unwise to 

 extrapolate and assume that this large imbalance is responsible for the 

 observed organic accumulation at Barrow. Such an imbalance would 

 generate the observed organic accumulation in 160 years, whereas radio- 

 carbon dating indicates that accumulation has occurred for thousands of 

 years (Chapter 1). August was 5°C cooler in 1971 than the long-term 

 average and may have reduced respiration below the norm and partially 

 accounted for the net carbon gain measured in that year. June and July, 

 when most of the growth and photosynthesis occur, were close to the 



