Constraining ventilation during deepwater formation using deep ocean measurements of the dissolved gas ratios ~(40)Ar/~(36)Ar,N_2/Ar, and Kr/Ar

摘要

The concentration of inert gases and their isotopes in the deep ocean are useful as tracers of air-sea gas exchange during deepwater formation. △ Kr/Ar, △N_2/Ar, and δ~(40)Ar were measured in deep profiles of samples collected in the northwest Pacific, subtropical North Pacific and tropical Atlantic oceans. For the ocean below 2000 m, we determined a mean △Kr/Ar composition of -0.96% ± 0.16%, a mean △N_2/Ar of 1.29% ± 0.21% relative to equilibrium saturation, and for δ~(40)Ar a value of 1.188%0 ± 0.055%o relative to air. These data are used to constrain high-latitude ventilation processes in the framework of three-box and seven-box ocean models. For the three-box model tracer data, we constrain the appropriate surface area of the high-latitude region in both models to be 3.6% (+2.5%,-1.7%) of ocean surface area and the bubble air injection rate to be 22.7 (+8.8, -7.3) mol air m~(-2)yr~(-1). Results for the seven-box model were similar, with a high-latitude area of 3.3% (+2.2%, -1.3%). Our results provide geochemical support for suggestions that the effective area of high-latitude ventilation is much smaller than the region of elevated preformed nutrients and demonstrate that noble gases strongly constrain the ocean solubility pump. Reducing high-latitude surface area weakens the CO_2 solubility pump in the box models and limits communication between the atmosphere and deep ocean. These tracers should be useful constraints on high-latitude ventilation and the strength of the solubility pump in more complex ocean general circulation models.