Joint International Conference on Long-term Experiments ...

the maximum of CO2 have the tendency to be larger than that for O2. We introduce the
following question at which we must give a response: which are the relative
contributions of the biological and physical processes to this distribution of gases.
From the measurements it can be seen that the N2O distribution is near to the
atmospheric equilibrium on the most latitudes, with the exception of those closed to the
equator, where N2O is in a big quantity that would imply the existence of an oceanic
source. We need to see which this source is. To answer such questions we need to know
the gases solubilities, that tell us at which concentrations are the gases. We must also
discuss about the gases exchange rates that determines how rapidly a corps immersed in
water will be in equilibrium with the atmosphere at the ocean surface. In a future paper
we will discuss also about the biological processes that take place inside the ocean,
processes that together with the physical ones force the gases to go out from the
equilibrium state with atmospheric air.
2. THE GASES SOLUBILITIES
We need to estimate the gas concentration in mmol ⁄ m 3 in sea water, which is not in
equilibrium with the gas from wet air above of ocean. The gases atmospheric
concentrations are given as partial pressures in physical atmosphere (atm) defined by
the relation:
pA = χA ⋅P (1)
where the molar fraction χA is the moles number of the component A in the unity of air,
P being the total atmospheric pressure in atm. The most suitable definition for the gases
solubility is given as:
CA = SA ⋅pA = SA⋅χA⋅P (2)
where CA is the solution concentration of the component A in mmol⋅m -3 , equal with 1
μmol⋅l -1 ; SA is the solubility in mmol⋅m -3 ⋅atm -1 . This parameter is related to Bunsen
coefficient β or to the parameter that is function of solubility, F. These parameters could
be related. In the Table nr.2 the equation and the coefficient for calculation of Bunsen
coefficients and of solubility fractions F for some gases are given. The solubility decays
with the increasing of the temperature for all gases.
3. THE GAS EXCHANGE
The vertical motions in the atmosphere and in the ocean are intensively suppressed near
the air-ocean water interface. There were been proposed a variety of models to explain
the effect of this phenomenon on the gas transfer transverse to the air-water interrface.
We will take into consideration the stagnant film model. This model supposes that the
turbulence suppression at the sea-air interface could be represented by molecular
diffusion inside a stable film of finite depth, both in ocean and in the atmosphere. This
model could be easier visualized and gives us the possibility of a direct discussion for
the relative importance of the atmospheric and ocean boundary layers. The model of the
stagnant film represents the transition from the turbulence inside the free surface fluid to
the molecular diffusion from inside the stable film by a simple structure made from two
layers, illustrated in the Fig.1. If we take into account the fact that doesn’t exist nor
sources nor sinks inside the film, it may be affirmed that fluxes in these films will be
given by the first Fick law:
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