A latitude-depth, circulation-biogeochemical ocean model for paleoclimate studies. Development and sensitivities

Abstract

We extend a zonally-averaged, global ocean circulation model to include a simple description of the cycles of organic carbon and CaCO3. The circulation in the model is first calibrated so that basin mean vertical profiles of temperature, salinity and radiocarbon agree closely with data for the modern oceans. Then, the capability of the model to reproduce the observed largescale distribution of five biogeochemical tracers (phosphate, oxygen, total dissolved inorganic carbon (DIC), alkalinity (ALK) and δ13C of DIC) is investigated. If organic carbon is transported only as fast-sinking particles with a remineralization profile constrained from sediment trap data, large PO4excesses and anoxia are simulated in subsurface waters in the equatorial Pacific and Indian Oceans. As in 3-dimensional models, these features disappear if a significant fraction (σ) of organic carbon is allowed to be exported away from production sites as labile dissolved organic carbon (DOCl). With σ= 0.5 and an ocean mean DOCl of 10 mmol m-3, the latitude-depth distributions of PO4 and apparent O2utilization in the different basins are in agreement with climatological data. The basin mean vertical profiles of DIC, ALK and δ13C diccompare favourably with observations in the modern oceans. The model predicts a global new production of 6.3–10.8 GtC yr-1, a rate consistent with data- and model-based estimates.