![]() Tomczak, Identification of diapycnal mixing through optimum multiparameter analysis, 2: Evidence for unidirectional diapycnal mixing in the front between North and South Atlantic Central Water, J. Tomczak, Ventilation processes and water mass ages in thermocline of the southeast Indian Ocean, Geophys. J., 3H and 3He in the Beta Triangle: Observations of gyre ventilation and oxygen utilization rates, J. J., On the climate of a subtropical gyre: Decadal timescale variations in water mass renewal in the Sargasso Sea, J. Tomczak, Optimum Multiparameter Analysis of the water mass structure in the western North Atlantic Ocean, J. A., Circulation of Antarctic Intermediate Water in the south Indian Ocean, Deep Sea Res., Part I, 40, 2021– 2042, 1993. Bullister, A chlorofiuorocarbonsection in the eastern North Atlantic, Deep Sea Res., 39 11–12, 1857– 1883, 1992. Nicolson, A practical method for numerical integration of partial differential equations of the heatconduction type, Proc. Chester, R., Marine Geochemistry, 698, Chapman and Hall, New York, 1990.Peng, Tracers in the Sea, 690, Lamont-Doherty Geol. Sarimento, Redfield ratios of remineralization determined by nutrient data analysis, Global Biogeochem. It takes ICW some 25–30 years to reach 110☎. While most SAMW joins the equatorward gyre movement of the southeastern Indian Ocean, some of it propagates westward through turbulent diffusive mixing, reaching 55☎ after 15–20 years. Pure ICW is present only in the thermocline of the region 48°–55☎, with increasing age with depth, confirming the subduction theory. In the eastern part of the south Indian Ocean, SAMW dominates the oceanic thermocline and is found to be about 5 years old. It is shown that the convective formation of SAMW is a major ventilation mechanism for the lower Indian thermocline. These distinct water masses have different formation mechanisms but similar temperature/salinity characteristics. In the thermocline, Indian Central Water (ICW) and Subantarctic Mode Water (SAMW) meet and mix. ![]() We apply the method to hydrographic data along World Ocean Circulation Experiment section 15 in the south east Indian Ocean. The age distribution allows us to determine pathways of water masses, which differ from simple advection trajectories because the age is determined by a combination of advective and diffusive processes. We define the age of a water mass as the time a water parcel needs to spread from its source region, where it received its individual tracer characteristics, to the point of observation. It enables us to follow water mass movements in greater detail than with other methods, which give only the combined pseudoage of a water mass mixture. We present a new method based on a combination of optimum multiparameter analysis and CFC/oxygen mixing analysis to determine the ages of water masses in regions of mixing. ![]()
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