View Full Version : Nutrient Diffusion

12th February 2005, 08:59 AM
Does any body have any reference or notes on nutrient diffusion.
Can you please let me know the conditions for diffusion to take place.
here we are in a condition with warm less saline water on the top with high nutrient content at surface.Please do advise on this....
Anand and Sabu

12th February 2005, 03:26 PM
Hi Anand & Sabu,

I am not sure whether u are talking about the Biological conditions.
From the physical point of view, Diffusion of any of these Biological
terms (lets call them as Tracers) can readily occur under any
circumstances. In your case, the ocean is stabily stratified (with
warm and less saline water in the surface), so the convective
processess (mixing) may not be occuring or weak. The Tracer Diffuses
by 'modelcualr diffusion (determined by kinematic diffussive term)
and Turbulent diffusion. For simplicity if you neglect the horizontal
advection, vertical convection and hoizontal diffusion, the system is
like a 1-D model as,

dN/dt = d/dz (nu.dN/dz) - d/dz(w.N)

the first term in the R.H.S is the molecular diffusion with
'kinematic diffusion coef -> 'nu'.

the second temr in R.H.S is the 'turbulent diffusion'. If you go for
a first order closure, you can simply re-write this as - d/dz(w.N) =d(K.dN/dz)/dz
Here the 'K' is the turbulent diffusion coeff. So you dont need
any velocity components, and all the terms are known.

If the convection (mixing) is relatively weak, the major term determining
the spread of the Tracers (in your case Nutrient) will be these
diffusion terms. This is the case if you neglect the horizontal advective
terms. (You can add horizontal diffusion in a similar fashion as it done
for vertical. )

A useful reference about these processess is listed here.(item 4) (http://www.oceanographers.net/forums/showthread.php?p=131)

ah, one more thing, if you are concerned with other chemical processess
like Nutrient growth, uptake etc, you will have to add that terms
as source terms.


13th February 2005, 05:02 AM

Its quite informative..
i need to know more on the insitu conditions that should prevail on diffusion.
it happened that we are having two regions, one at northern side with less saline and high temperature and at southern side salinity is little higher by (0.2psu) and temperature almost same. but we could trace this intrusion only in the northern transects. Hence I need some references on that insitu conditions...

What vinu replied me is ok. But I need some more reference of not models but insitu datas.