Help! Estimates of CO2 uptake ...

[Gilles.Hosch at fao.org]

dear val,

i'd like to come back to your original question on CO2 uptake in the estuary
of the amazon. i agree that the sediments are not spread "down" the coast -
it sure is the other way around.

the original question was "Do you happen to know what the rate of absorption
of carbon dioxide by the sea within 1 km of the shore is likely to be during
the day in a large tropical river estuary (in this case the Amazon)?" 

upon checking my atlas of the sea yesterday, after viviane had proved me
wrong on sediment transport issues pertaining to the amazon, it occured to
me, that you actually cannot give a general answer to the question (i.e.
large tropical river estuaries). there is a number of factors to consider:
one is the amount of sediment which the river carries. too heavy a load of
sediment will prevent prolific algal productivity because of light
extinction. then there's the chemistry of the river waters that are of
essence. in brazil for instance, and viviane may correct me if i'm wrong,
there are essentially two types of rivers, the white and the black rivers.
white rivers drain geologically recent areas, like the cordillera (which is
amongst the "youngest" geological formations on earth) and carry high loads
of sediments, while "black" rivers (like the rio negro) drain wheathered
geological formations (of which the guayana shield in the north and the
brazilian shield in the south) and carry virtually no sediments at all. the
chemistry of the waters can thus differ widely among tropical rivers of the
same area, and this will play a critical part in the fueling of marine
primary production near the mouth of an estuary. if the estuary feeds into
an upwelling area, primary productivity offshore will be high, and not
because of the river discharge per se. in south america, the main upwelling
area is the west coast off peru and chile. the amazon feeds into an area of
relatively low primary productivity.

you say, "within 1 km of the shore" - which, for the amazon again, is a bit
of a tricky one, since the estuary is like a country in itself, extremely
wide and made up of a range of smaller and larger islands. i think, whatever
your friend is looking at, he will have to kneel down and pinpoint locations
in the estuary which are of interest, and look at the hydrology of those
areas, as i would guess that there will be substantial spatial and seasonal
variations in all parameters of importance between locations. he might get
his threshold CO2 uptake rates in some parts of the delta, and not in
others. i'd still be guesstimating that CO2 uptake rates related to primary
productivity will be very low within the area he is looking at. i'd be
interested in getting to know the final verdict!

cheers,

g

-----Original Message-----
From: Frank E. Muller-Karger [mailto:carib at carbon.marine.usf.edu]
Sent: Wednesday, March 21, 2001 10:05 PM
To: Viviane Testa
Cc: coral-list at coral.aoml.noaa.gov
Subject: RE: Help! Estimates of CO2 uptake ...


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