Constraining ventilation during deepwater formation using deep ocean measurements of the dissolved gas ratios 40Ar/36Ar, N2/Ar, and Kr/Ar

The concentration of inert gases and their isotopes in the deep ocean are useful as tracers of air-sea gas exchange during deepwater formation. Delta Kr/Ar, Delta N-2/Ar, and delta Ar-40 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 Delta Kr/Ar composition of -0.96% +/- 0.16%, a mean Delta N-2/Ar of 1.29% +/- 0.21% relative to equilibrium saturation, and for delta Ar-40 a value of 1.188% +/- 0.055% 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 CO2 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.