Linkages between upwelling and biological pump in the CMIP5 earth system models

Our understanding of the global carbon cycle often relies on idealized, conceptual models. Classic box models emphasize the balance between upwelling nutrient supply and downward export production. Upwelling of nutrient-rich deep water sustains the biological productivity, and the downward export of organic matter must balance the upwelling supply at steady state. Recent development of Earth System Models (ESMs) provides a unique opportunity to refine our understanding based on conceptual models. In this study we analyze a subset of ESMs participating the Coupled Model Intercomparison Project phase 5 (CMIP5) to test the vertical balance between the upwelling nutrient supply and the downward export production on interannual timescales. In particular, we analyze year-to-year variation of the biome-scale upwelling of phosphorus (i.e. integrated vertical advection) and the sinking particulate carbon simulated by a subset of CMIP5 models. We examine the correlation between the detrended anomalies of upwelling and export production globally and regionally. Four out of seven models show statistically significant, moderately positive correlations between the globally integrated upwelling and export production, qualitatively consistent with the box model. In the equatorial upwelling regions, all models show positive correlation between regional upwelling and export production. In the permanently stratified subtropical oceans, majority of models show significant, moderately negative correlations. In the Southern Ocean biomes, the models do not show clear relationship except for the seasonal ice zone with a moderate positive correlation. These results indicate regionally specific linkages between biological pump and climate variability that are more complex than the simple vertical balance.