Global net community production estimated from the annual cycle of surface water total dissolved inorganic carbon

Global net community production is determined, for the first time, from the decrease in salinity (S)ߚnormalized total dissolved inorganic carbon (NC T = C T × 35/S) inventory in the surface mixed layer corrected for changes due to net airߚsea CO 2 exchange and diffusive carbon flux from the upper thermocline. Changes in the mixed layer NC T inventory are estimated using a derived annual cycle of NC T and global records of the mixed layer depth. The annual NC T cycle is deduced from regional algorithms relating NC T to sea surface temperature (SST) and nitrate (NO 3 − ), along with global records of seasonal mean SST and NO 3 − , and from the monthly mean surface partial pressure of CO 2 and total alkalinity fields using thermodynamic models. The two methods show similar regional trends and yield global net community production estimates of 6.7 and 8.0 Gt C (1 Gt C = 1 × 10 12 kg carbon), respectively. The two global estimates are not significantly different and represent an 8–month period of 1990 (warming period) during which the mixed layer NC T concentration decreases. However, the estimates do not account for net community production during a 4–month cooling period. Ratios of net community production during the warming and cooling periods are estimated from multiyear sediment trap data at the Hawaii Ocean Timeߚseries (228N, 1588W) and Ocean Weather Station P (50°N, 145°W) sites. Global extrapolation of these ratios yields annual rates of net community production of 9.1 ± 2.7 and 10.8 ± 2.7 Gt C yr −1 .