The joint water-mass and transit-time distribution contains complete information about the transport processes in the flow. The theory thus includes the classical oceanographic idea of water-mass analysis and extends it to allow for a distribution of transit times from the sea surface. The boundary propagator has the interpretation of the joint water-mass and transit-time distribution from the sea surface. It allows any passive tracer field with an atmospheric source to be constructed by superposing sea surface contributions with a generalized Green's function called the boundary propagator of the passive tracer equation. The important sources are labeledĪ general theory to describe and understand advective and diffusive ocean transport is reported.

The right panel shows the locations of all sources with the area enclosed by the ellipse proportional to the water-mass fraction for that component. The important sources are labeled with the source-location number, water-mass fraction, and mean transit time (years) for that source. The central panel shows the water-mass composition for all 32 sources shown in Fig. The transit-time distribution and the mean transit time (years) for all surface sources are shown with the dashed line and in the top right corner, respectively. In each case, the left panel shows the transit-time distributions for the important water sources (those that contribute 5% or more to the total composition estimated with transit times up to 200 yr).

MICOM water-mass composition–age distribution for (a) eastern North Atlantic mode water at 40°N, 20°W (26.92 ≤ σ θ ≤ 27.13 kg m −3), (b) eastern North Atlantic mode water at 35°N, 30°W, (c) North Atlantic deep water at Flemish Cap 45°N, 50°W (27.85 ≤ σ θ ≤ 27.90), (d) subtropical mode water (26.35 ≤ σ θ ≤ 26.92), (e) subpolar mode water (27.58 ≤ σ θ ≤ 27.85), and (f) the whole model domain, excluding the mixed layer.

Age of water masses