Southern Ocean CO2 outgassing and nutrient load reduced by a well-ventilated glacial North Pacific

The biogeochemistry of Southern Ocean surface waters has global impacts on nutrient distributions, the carbon cycle, and climate, motivating study of its underlying controls and changes under altered climate states. Today, poorly-ventilated North Pacific waters supply the majority of carbon and nutrients upwelling in the Southern Ocean, outpacing the rate of biological carbon assimilation and fueling CO ₂ outgassing. A means of reducing this carbon/nutrient supply is central to explaining the improved biological pump efficiency evidenced in paleo-proxy reconstructions and invoked in theories for glacial CO ₂ change. Past studies predominantly attribute reduced glacial carbon/nutrient load of Southern Ocean surface waters to local physical processes (e.g., reduced wind-driven upwelling or enhanced stratification). Here we propose a complementary mechanism in which the carbon/nutrient load of the source waters feeding the Southern Ocean surface is reduced remotely, prior to being upwelled. Comparing glacial North Pacific and Southern Ocean proxy records, alongside results from 3 different Earth System Models, we show that improved ventilation of the glacial North Pacific directly reduces carbon/nutrient-delivery to and CO ₂ outgassing in the Southern Ocean surface. This highlights a novel interhemispheric influence on the biogeochemical state of the Southern Ocean, which may play a key role in glacial CO ₂ change.