Marine radiocarbon reservoir age simulations for the past 50,000 years revisited

Marine radiocarbon ( ¹⁴ C) archives are depleted relative to the atmospheric ¹⁴ C reservoir, which is commonly expressed as the Marine ¹⁴ C Reservoir Age (MRA). Here we apply the Earth system model of intermediate complexity CLIMBER-X equipped with ¹⁴ C to simulate the MRA evolution over the past 50,000 years. Globally, our simulated MRAs range from 400 to 1200 ¹⁴ C years and are systematically lower than previous estimates from the uncoupled LSG ocean general circulation model, which is mainly due to stronger ocean ventilation in CLIMBER-X. Short-term MRA variations are dominated by changes in cosmogenic ¹⁴ C production, while glacial-interglacial climate variations exert slower and damped effects. From the coupled evolution of atmospheric and marine ¹⁴ C in these simulations we infer that during the Laschamps geomagnetic excursion the interhemispheric ¹⁴ C gradient in the atmosphere was up to twice as large as previously estimated.