Abstract
ABSTRACTA former publication proposed an idealised view of the global ocean ventilation consisting in a flow through a porous pipe with decreasing section (a leaky funnel). The agreement between the domain-averaged ages as obtained with a coarse-grid 3-D ocean general circulation model (OGCM) and the leaky funnel is excellent. Further, the latter allows to infer characteristic scales, which are consistent with the current knowledge of the ocean ventilation. However, the method, based on numerical experiments in which the circulation fields of the OGCM were artificially modified, is questionable. Here, we revisit the leaky funnel and base our study on the global water age distribution , where is the ocean volume fraction with age in the interval . The steady-state analytical solution for this distribution is shown to be in excellent agreement with numerical results from two coarse grid OGCMs: an outcome that helps strengthening the leaky funnel representation. The asymptotic analysis of suggests that, for large ages, water parcels have the same life expectancy, whatever their age. Further, the leaky funnel provides bulk characteristics of the circulation in OGCMs, which may serve as metrics in model intercomparison studies.
Highlights
The rate at which the ocean can sequester excess heat and carbon from the atmosphere is determined by its ventilation, i.e. the renewal of interior waters by seawater that has been in contact with the atmosphere
The method of MD08 was questionable since it disregards the ocean general circulation model (OGCM) internal dynamics
The good correlation between the age distributions in the leaky funnel and in the OGCMs provides a further assessment of the leaky funnel
Summary
The rate at which the ocean can sequester excess heat and carbon from the atmosphere is determined by its ventilation, i.e. the renewal of interior waters by seawater that has been in contact with the atmosphere. In the context of climate and environmental studies, it is of importance to better assess the ocean ventilation rate and its properties. The age, which measures the time needed for water parcels to travel from the ocean surface to the interior, is the appropriate tool for this purpose. Of use are numerical simulations and field measurements of appropriate tracer concentrations. The intrinsic complexity of ocean circulation and the huge amount of information provided by ocean general circulation models (OGCMs) make it difficult to extract the most relevant information on spatial and temporal scales characterising ventilation. Low-order representations of the world ocean circu-
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