VERTEX: carbon cycling in the northeast Pacific

Particulate organic carbon fluxes were measured with free-floating particle traps at nine locations during VERTEX and related studies. Examination of these data indicated that there was relatively little spatial variability in open ocean fluxes. To obtain mean rates representative of the oligotrophic environment, flux data from six stations were combined and fitted to a normalized power function, F = F100 (z/100)b; e.g. the open ocean composite C flux in mol m−2 y−1 = 1.53 (z/100−0.858 with depth z in meters. It is shown that the vertical derivative of particulate fluxes may indicate solute regeneration rates, and accordingly regeneration rates for C, H and N were estimated. Oxygen utilization rates were also estimated under the assumption that 1.5, 1.0 and 0.25 moles of O2 were used for each mole of N, C and H regenerated. Regeneration ratios of these elements were depth-dependent: i.e. N:C:H:−O2 = 1.0 N: 6.2 (z/100)0.130 C: 10.0(z/100)0.146 H: [1.5 + 6.2 (z/100)0.130 + 2.5 (z/100)0.146]−O2. Comparisons of our rates with those in the literature indicate that trap-derived new productivities in the open Pacific (≈1.5 mol C m−2 y−1) are substantially less than those estimated from oxygen utilization rates in the Sargasso Sea (≈4 mol C m−2 y−1). A hypothesis is presented which attempts to explain this discrepancy on the basis of the lateral transport and decomposition of slow or non-sinking POC in the Sargasso Sea. Data gathered during the VERTEX studies are also used for various global estimates. Open ocean primary productivities are estimated at 130 g C m−2 y−1 which results in a global open ocean productivity of 42 Gt y−1. Organic C removal from the surface of the ocean via particulate sinking (new production) is on the order of 6 Gt y−1. Fifty percent of this C is regenerated in the upper 300 m of the water column. The ratio of new production (measured with traps) to total primary production (measured via 14C) is 0.14. It is concluded that the 14C technique yields reasonable estimates of primary productivity provided that care is taken to prevent heavy metal contamination.