Reefs as Source or Sink of CO2

[Craig Bingman]

On Tue, 13 Feb 1996, David Kesler wrote: 

> I am teaching a course, "Coral Reef Ecology", and we will be discussing Kayanne  
> et al.'s 1995 Science article, "Diurnal changes in the partial pressure of  
> carbon dioxide in coral reef water".  Are you aware of any responses to their  
> article or more recent work dealing with this topic? 

I'll defer to the judgement of others, as I know that some of the  
individuals sending technical comments are also on the list and may  
respond here as well, but what struck me about the article was that the  
body of water which was isolated seemed to have many things growing in  
it besides corals.  I remember seeing extensive areas of seagrass and  
other "green" things in the water in the diagrams of the area. 

So, my gut reaction to the article was that the "unexpected" results  
reported might have a lot more to do with the CO2 demand from the  
seagrass and other photosynthetic organisms than some problem with the  
orthodox view that the act of producing calcium carbonate from a solution  
in which the alkalinity is mainly in the form of bicarbonate produces  
carbon dioxide in addition to calcium carbonate.  Or that coral can be net  
producers of carbon dioxide during the day when the rate of calcification  
overtakes the photosynthetic carbon dioxide demand. 

It is sort of difficult to work one's way around these equations: 

(1)	Ca++ + 2(HCO3-) --> CaCO3 + H2O + CO2 
(2)	Ca++ + CO3--    --> CaCO3 

Since the bulk of the alkalinity in seawater is in the form of HCO3-  
ions, what you get is mainly equation 1), with some of equation 2). 

The body of water surveyed was also fairly northern and it is not clear  
that the species of corals contained were among the more rapidly calcifying  
types. 

I'm sure others will have other things to say.  ;) 

Craig Bingman