Modeling dissolved organic carbon and carbon export in the equatorial Pacific Ocean

Abstract

The newly built CoSiNE-31 ecosystem model developed for the Pacific Ocean is employed here to evaluate carbon cycling in the equatorial Pacific upwelling region. This model explicitly includes 31 state variables capable of reproducing key biogeochemical features in this region, such as high-nutrient low-chlorophyll conditions. In the so-called Wyrtki Box (5°S–5°N, 90–180°W), the modeled area-averaged carbon export data show the predominance of the particulate organic carbon flux. This is consistent with observations, and amounts to 7.88 mmol C m–2 day–1 at the bottom of the euphotic zone (120 m water depth). Nearly as important is the dissolved organic carbon export flux, at 6.62 mmol C m–2 day–1. The modeled particulate inorganic carbon (PIC) export flux of 2.07 mmol C m–2 day–1 is much higher than the global average, indicating a key role of PIC sedimentation in the study region. The modeled carbon-to-nitrogen export ratio for particulate organic matter (POM) is 7.8, which is consistent with the Redfield ratio. The export ratio increases to 13.8 for dissolved organic matter (DOM). By implication, carbon export is markedly more efficient via DOM than via POM. This is the case also under simulated iron enrichment conditions, although there are measurable increases in carbon export efficiency for both DOM and POM.