Seasonal Change in Evaporation Rate

In the final experiment I simulate the effect of seasonal change in the evaporation rate by adding the sinusoidally varying fuel to the influx of water, fluxin. I leave fluxout unchanged at a value of 2 m/y. The influx is 

These three numerical experiments show how the waters of an evaporating lagoon respond differently to the different seasonal perturbations that might affect them. Some record of these perturbations might, in principle, be preserved in the carbonate sediments precipitated in the lagoon. All three perturbations—productivity, temperature, and evaporation rate— cause seasonal fluctuations in the saturation state of the water and in the rate of carbonate precipitation. Temperature oscillations have little effect on the carbon isotopes. Although seasonally varying evaporation rates affect 14C, they have little effect on 13C. Productivity fluctuations affect both of the carbon isotopes. 

In this chapter I explained how isotope ratios may be calculated from equations that are closely related, but not identical, to the equations for the bulk species. Extra terms arise in the isotope equations because isotopic composition is most conveniently expressed in terms of ratios of concentrations. I illustrated the use of these equations in a calculation of the carbon isotopic composition of atmosphere, surface ocean, and deep ocean and in the response of isotope ratios to the combustion of fossil fuels. As an alternative application, I simulated the response of the carbon system in an evaporating lagoon to seasonal changes in biological productivity, temperature, and evaporation rate. With a simulation like the one presented here it is quite easy to explore the effects of various perturbations. Although not done here, it would be easy also to examine the sensitivity of the results to such parameters as water depth and salinity. 

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Figure 6-10 shows how the various elements of the carbon system respond to the seasonal change in evaporation rate. Although the fluctuations in carbonate ion concentration cannot be seen on the scale of this figure, examination of the numbers shows that the amplitude of the carbonate fluctuation is about 3 percent, comparable to the amplitude of the... 

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