Carbon cycle sensitivities in modeling the biological pump

Sensitivities in modeling the biological pump in the GISS climate model are explored here. Results are presented from twin control simulations of CO2 gas exchange between the ocean and the atmosphere using two ocean models coupled to the same atmosphere (modelE). The two ocean models (Russell ocean model and Hybrid Coordinate Ocean Model, HYCOM) use different vertical coordinate systems, and therefore different representations of column physics. Both variants of the GISS climate model -- modelE with the Russell ocean and modelE with the HYCOM ocean -- are coupled to the same ocean biogeochemistry module (the NASA Ocean Biogeochemistry Model, NOBM) which computes prognostic distributions for biotic and abiotic fields that influence the air-sea flux of CO2 and the deep ocean carbon transport and storage. In particular, the model differences due to remineralization rate changes are compared to differences attributed to physical processes modeled differently in the two ocean models such as ventilation, mixing, eddy stirring and vertical advection. The Southern Ocean emerges as a key region where the CO2 flux is as sensitive to biological parameterizations as it is to physical parameterizations.