Xref: utzoo sci.bio:4138 sci.aquaria:998 sci.environment:8941
Path: utzoo!attcan!uunet!ogicse!uwm.edu!grce!jeff
From: jeff@grce.UUCP (Jeff Frank)
Newsgroups: sci.bio,sci.aquaria,sci.environment
Subject: Re: coral reefs, C02, food, and farming.
Message-ID: <367@grce.UUCP>
Date: 10 Dec 90 16:06:23 GMT
References: <720@sierra.stanford.edu> <90337.112001JAHAYES@MIAMIU.BITNET>
Reply-To: jeff@grce.UUCP (Jeff Frank)
Followup-To: sci.bio
Organization: GENROCO, Inc., Slinger, WI
Lines: 38

In article <90337.112001JAHAYES@MIAMIU.BITNET> JAHAYES@MIAMIU.BITNET (Josh Hayes) writes:
> 
>I am a little concerned about the blithe assertion that calcium is
>not limiting here; releasing Ca from CaHCO3 leaves free bicarbonate
>ions floating about, which as you recall from your human physiology
>class associates with free hydrogen ions to form carbonic acid, which
>dissociates to water and CO2....thus regenerating CO2. I dunno how
>seriously this process would bollix up the sinking of CO2 on the whole,
>but it needs examining.

Your concern is well placed but you should take into account the effect
of pH.  This "regeneration" you refer to is a function of protons 
(hydrogen ions) present in solution.  At pH 8.3 (I think I remember
reading somewhere recently this is the average pH of oceans) there
are relatively few protons to "liberate" CO2 from HCO3-.

I have in front of me a graph entitled "The Relationship of Hydrogen
Ion Concentration to the Percentage of Total Carbon Dioxide in Each of
Its Forms in Water" (adapted from Emerson, R. and Green, L., 1938.)

It depicts pH from 4-12 along X-axis and per cent of total CO2 along
Y-axis.  There are 2 bell shaped curves.  One begining at pH 4,
percentage zero rising in sigmoid fashon to its asymptote at pH 8,
falling in sigmoid path to zero at pH 12.  This is the HC03- 
percentage of total CO2.  The other curve depicts the free CO2 and
CO3-- percentage of total CO2.  It of course begins at 100 per cent
CO2 at pH 4 and drops conversely to HCO3- curve.  At pH 6.5 there
is half CO2 anf half HCO3-.  At pH 8 we have 100% HCO3- so, there is
zero CO2.  Since free CO2 is no longer viable at higher pH, the
"CO2 or CO3--" curve now depicts percent CO3--.  At pH 10 there is
half HCO3- and half CO3--.  At pH 12 there is 0% HCO3- and 100%
CO3--.

This means that at typical ocean pH, any CO2 introduced will be
immediately converted to HC03-.  As pH would lower (as would happen
with tremendously high CO2 additions) the buffering effect would get
weaker and weaker, but it would take an awful lot of CO2 to do
the job.