9/13/2023 0 Comments Age of water masses![]() In this vertically discretised, laminar framework, potential vorticity (PV) conservation facilitates a bijective relationship between the origin and destination of a water parcel. This idea was developed theoretically over the following decades in analytical models ( Welander, 1959, 1971 Luyten et al., 1983). From charts of hydrographic sections, Iselin ( 1939) inferred communication between isopycnals at depth and their outcrops. Thermocline ventilation and water mass formation is an area with a long history of inquiry. Tracing the pathways of newly ventilated ocean water masses is a multidisciplinary pursuit, for which an entire toolbox of methods has been developed. The intricate process by which the atmosphere and ocean exchange properties has decisive effects on oceanic and atmospheric circulation, biochemistry, and climate. It is shown that while model NADW has two distinct outcrops (in the Arctic and North Atlantic), its formation primarily takes place in the subpolar Labrador and Irminger seas. A bed of more persistent NASMW is detected below the mixed layer with an expected age of 8.7 years. ![]() Model NASMW is shown to have an expected age of 4.5 years and is predominantly eradicated by internal processes. Two test cases are detailed, examining the creation and fate of North Atlantic Subtropical Mode Water (NASMW) and North Atlantic Deep Water (NADW) in a 2 ∘ configuration of NEMO run with repeated annual forcing for up to 400 years. To represent surface (re-)ventilation, we optionally decrease the tracer concentration in the surface layer and track this concentration removal to produce a ventilation record. By terminating dynamic feedbacks in NEMOTAM, tagged water can be tracked forward and backward in time as a passive dye, producing a probability distribution of pathways and origins, respectively. In particular, NEMOTAM, the tangent-linear and adjoint counterpart to the NEMO ocean general circulation model, is modified to allow passive-tracer transport. ![]() In this study, we present a newly developed, probabilistic tool for offline water mass tracking. Water mass ventilation provides an important link between the atmosphere and the global ocean circulation. ![]()
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