Carracedo, L. I., Mercier, H., McDonagh, E., Rosón, G., Sanders, R., Moore, C. M., Torres-Valdés, S., Brown, P., Lherminier, P., & Pérez, F. F. (2021). Counteracting Contributions of the Upper and Lower Meridional Overturning Limbs to the North Atlantic Nutrient Budgets: Enhanced Imbalance in 2010. Global Biogeochemical Cycles, 35(6), e2020GB006898. https://doi.org/10.1029/2020GB006898
Summary
The North Atlantic Ocean is a major reservoir which absorbs atmospheric carbon dioxide (CO2) due in part to the extensive plankton (microscopic marine algae) blooms which form there supported by nutrients supplied by ocean circulation. Hence, changes in ocean circulation and/or stratification (separation of the water column into layers with different densities caused by differences in temperature or salinity or both) may influence biological production and carbon export into the deep ocean. In this study, the inorganic nutrient budgets for 2004 and 2010 are evaluated in the North Atlantic based on observations from the transatlantic the Greenland-Portugal section. The water column nutrient budgets were split into upper and lower limbs. The authors found that in 2010 an anomalous circulation led to an enhanced northward transport of more nutrient-rich waters by the upper limb. This anomalous circulation event favoured an enhancement of the nutrient consumption and associated biological CO2 uptake, which represents a 50% of the mean annual sea–air CO2 flux in the region. These results indicate that the upper limb modulates the biological carbon uptake, and the lower limb modulates nutrient inventories in the North Atlantic.