Dataset belonging to "Glacial mid-depth carbon storage and the role of Northern African upwelling in the last deglaciation" Version 4

Upwelling systems are important components of the carbon cycle due to their role in redistributing CO2 from mid-depth to the ocean surface and thereby affecting sea-atmosphere exchange of CO2. This latter flux is affected by multiple factors, involving oceanography and local climate conditions, that have also contributed to glacial-interglacial variability of atmospheric pCO2. Along the shore of northwestern Africa, the Canary Current Upwelling System (CCUS) brings the nutrient- and CO2-rich Antarctic Intermediate Water (AAIW) to the surface. Today, upwelling intensity in this region is characterized by seasonal fluctuations linked to the migration of the Intertropical Convergence Zone. Due to differences in biology-driven CO2 uptake, ocean-atmosphere interaction in this region differs between the northern and southern cells, featuring net CO2-sink and CO2-source properties, respectively. To better understand glacial-interglacial processes of the North Atlantic tropics, we reconstructed temperature and pCO2 based on both organic (UK ʹ37, δ13C of alkenones) and inorganic proxies (Mg/Ca and δ11B of foraminiferal carbonate). These proxy signal carriers allow constraining conditions both in the surface (using alkenones and T. sacculifer) and subsurface (using G. bulloides). Subsurface carbon contents, upwelling rate and the position of the Cape Verde Frontal Zone (CVFZ) all affect the carbon speciation of the upwelled water. The 120 ka BP records of reconstructed pCO2 suggest that carbon dynamics of the region were very similar to present-day conditions prior to the glacial, between approximately 120 and 75 ka BP. During the Last Glacial, however, ocean circulation and water mass distributions differed substantially from modern conditions. Expansion of the AAIW during the glacial affected upwelling intensity and inorganic carbon chemistry of these upwelled waters. Our records provide evidence for enhanced carbon storage at mid-depth from the early stage of the glacial onwards and they also show that this did not contribute to appreciably local outgassing until approximately 30 ka BP. An efficient biological carbon pump fuelled by enhanced nutrient supply from the upwelled waters as well as micro nutrients from Saharan dust and river runoff, could effectively retain carbon in this region. A reduction in local nutrient sources during the later phases of the Last Glacial eventually resulted in the release of carbon stored at mid depth of the CCUS and hence, potentially contribute to the onset of the last deglaciation.