Salinity as a Conservative Tracer

All figures are available on the companion website in color (if applicable). 

The global heat cycle drives the hydrological cycle, which in turn controls the salinity of seawater. The most important contributor of heat to the crustal-ocean-fectory is solar radiation. The flux of solar radiation that reaches Earth is termed insolation. Only a fraction of the incoming solar radiation reaches Earth s surfece, because a large portion is either reflected or absorbed by the atmosphere. That which reaches Earth s surface is also either reflected or absorbed. In the end, about half of the incoming radiation is absorbed by the rocks and water on Earth s surfece. (A detailed heat budget is provided 

Latitudinal variations in insolation caused by differenoes in the angle at which the sun s radiation strikes Earth s surface. Source-. From Thurman, H. V. (1988). Introductory Oceanography, 5th ed. Merrill Publishing Company, p. 170. 

The latitudinal heat gradient in the atmosphere and ocean remains relatively constant over time despite the short-term and spatial variations in insolation. This steady state is maintained by the net transport of heat from low to high latitudes where it is radiated back into space. Atmospheric currents (winds) are responsible for about half of this meridional net transport of heat. The rest is accomplished by water movement in the 

Average sea-surface temperature (°C) (a) in winter (Jan-Mar) and (b) in summer (Jui-Sep). Source. After Reynoids, R. W., and T. M. Smith (1995). Journal of Climate 8, 1571-1583. (See companion website for coior version.) 

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One of the first applications of ocean radiocarbon data was as a constraint on the vertical diffusivity, upwelling, and oxygen consumption rates in the deep waters below the main thermocline. As illustrated in Figure 2, the oxygen and radiocarbon concentrations in the North Pacific show a minimum at mid-depth and then increase toward the ocean seabed. This reflects particle remineralization in the water column and the inflow and gradual upwelling of more recently ventilated bottom waters from the Southern Ocean. Mathematically, the vertical profiles for radiocarbon, oxygen (O2), and a conservative tracer salinity (5) can be posed as steady-state, 1-D balances ... 

A useful apphcation of preformed nutrient concentrations is that they are intrinsic to different water masses and sometimes can be used as conservative tracers. For example, the main sources of deep water in the Pacific Ocean are North Atlantic Deep Water (NADW), Antarctic Intermediate Water (AAIW) and Antarctic Bottom Water (AABW), all of which are at least partly homogenized in the Antarctic Circumpolar Water (AACW). It is not possible to determine how much of each of these sources contributes to Pacific deep water by using end member mixing of the conservative properties temperature and salinity because salinities of the end members are not sufficiently different. Since concentrations of DIP are well above detection limits in... 

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