Carbon distribution and fluxes during the SERIES iron fertilization experiment with special reference to the fugacity of carbon dioxide (fCO2)

Surface seawater fugacity of carbon dioxide (fCO2) was measured during the Subarctic Ecosystem Response to Iron Enrichment Study (SERIES), July 9–August 5, 2002. Three ships sampled the iron-fertilized waters near Ocean Station P (50°N, 145°W): the Canadian CCGS J.P. Tully (July 9–23, 2002), the chartered Mexican M/V El Puma (July 9–28, 2002), and the Japanese fisheries research ship M/V Kaiyo Maru (July 24–August 5, 2002). Data used here are from the CCGS J.P. Tully and the M/V Kaiyo Maru. From the onset of the experiment to the peak of the iron-induced diatom bloom on day 19, sea-surface fCO2 decreased from 350 to 265 μatm and average DIC concentration in the upper 30 m decreased from 2030 to 1990 μmol kg−1. Changes in fCO2 in and near the iron patch as observed from the CCGS J.P. Tully and later from the M/V Kaiyo Maru were used to estimate CO2 drawdown and air-sea fluxes, and in generating a carbon budget during the growth phase (days 3–19) of the experiment. Without considering patch dilution, sources of dissolved inorganic carbon to the patch (1.6±0.25 mol m−2) were nearly double the sum (0.87±0.34 mol m−2) of the sinks: accumulations of dissolved organic and particulate carbon, and the flux of particulate carbon to sediment traps below the patch. However, the budget is balanced after considerations of the effects of patch expansion on property concentrations within the patch. A comparison with other iron fertilization experiments from 1995 to present was made to assess the CO2 drawdown values.