What is the estimated annual tonnage of carbon dioxide absorbed by
molluscs in the formation of their calcium carbonate shells?

Hi knowitall22, 
 
Well, an interesting question but not one that lends itself to an easy
answer.
 
We couldn't find reference to molluscs in particular, most of the
information pertains to all calcium carbonate building organisms (for
example, foramaniferans) but you may find this information on the
carbon cycles helpful in your search for the answer. You'll find that
approximately 50 billion tons of carbon (183 billion tons of carbon
dioxide*) enters the water from the atmosphere. The organisms that use
the carbon dioxide, give off about 40 billion tons carbon (146 billion
tons of carbon dioxide) through their metabolism, which is a net
uptake of 10 billion tons by ocean life. After the organisms die, the
calcium carbonate of their shells continue to exist. Part of the
calcium carbonate disolves back into the water and the rest
precipitate to the ocean floor where it becomes part of ocean
sediments. The net rate at which this occurs is .2 billion tons of
carbon per year (.73 billion tons of carbon dioxide). So, if you are
asking what the net removal of carbon dioxide from the atmospheric
sink is through biological processes in the ocean into the sedimentary
sink, the answer would be .73 billion tons of carbon dioxide. But keep
in mind that eventually the calcium carbonate will again become part
of the atomosphere through the weathering of limestone and volcanic
activity.
 
*The equivilent weight of carbon in carbon dioxide can be calculated
by multiplying the weight in carbon by the molecular weight of carbon
dioxide divided by the molecular weight of carbon, so the weight in
carbon multiplied by
[16 + 2 x 12] / 12 = the equivilent weight in carbon dioxide.  
 
 
Additional Links: 
 
The Carbon Cycle: 
http://www.geog.ouc.bc.ca/physgeog/contents/9r.html 
 
noaa research: see figure one: 
http://www.oar.noaa.gov/spotlite/archive/spot_carbon.html 
 
We're glad to hear this is what you were looking for - thank you for
letting us know.  Wishing you the best in the New Year -
 
Sincerely, 
hummer 
 
Search Strategy: 
None. My son, a university wildlife biology student, is home for the
holidays and took a special interest in your question.

Actually, the formation of CaCO3, the so-called calcite pump,
liberates CO2, and there is a net increase from that process.

"Therefore, there must exist additional processes that keep the
concentration of CO2 in the surface ocean low. These are collectively
referred to as oceanic carbon \pumps" (Volk & HoĈert 1985). There are
three such pumps: (i) the solubility pump; (ii) the soft tissue, or
organic matter pump; and (iii), the calcite pump, and they maintain a
vertical gradient of total dissolved inorganic carbon (DIC) in the
water column. The solubility pump is due to the fact that warmer
waters are less soluble for CO2, i.e. both cold deep and cold
high-latitude surface waters are enriched in CO2 relative to the main
water masses of the \warmwater sphere". This leads to a reduction of
DIC in the surface waters. The soft tissue pump is due to the DIC
uptake during the formation of marine organisms. This organic matter
is constantly exported to the deep ocean in particulate and dissolved
form. This also tends to reduce the surface concentrations of DIC. The
third pump operates in the opposite direction. When organic matter
forms calcite shells (CaCO3), CO2- 3-ions are extracted from the water
column. Due to (10) this results in an increase of atmospheric CO2. In
combination, these three pumps lead to a reduction of the equilibrium
CO2- concentration in the atmosphere from 670 ppmv to 280 ppmv (Tab.
1)."

Thomas F. Stocker, Changes in the Global Carbon Cycle and Ocean
Circulation on the Millennial Time Scale, Barcelona, 2001

http://www.climate.unibe.ch/~stocker/papers/stocker01barc.pdf

"while CaCO3 production by marine organisms results in half of the DIC
from rivers being returned to the atmosphere and half being buried in
deep-sea sediments"
[...]
"Marine organisms also form shells of solid calcium carbonate (CaCO3 )
that sink vertically or accumulate in sediments, coral reefs and
sands. This process depletes surface CO3 2 , reduces alkalinity, and
tends to increase pCO2 and drive more outgassing of CO2 (see Box 3.3
and Figure 3.1). The effect of CaCO3 formation on surface water pCO2
and air-sea fluxes is therefore counter to the effect of organic
carbon production."
[...]
"Milliman (1993)* estimated a global production of CaCO3 of 0.7
PgC/yr**, with roughly equivalent amounts produced in shallow water
and surface waters of the deep ocean. Of this total, approximately 60%
accumulates in sediments. The rest re-dissolves either in the water
column or within the sediment."

**Pg = 10^15 grams, or 700000000000000 g

I.C. Prentice , et alia, The Carbon Cycle and Atmospheric Carbon
Dioxide, 2001

(*Milliman, J.D., 1993: Production and accumulation of
calcium-carbonate in the ocean - budget of a nonsteady state. Global
Biogeochemical Cycles, 7, 927-957.

http://www.bgc-jena.mpg.de/bgc_prentice/publi/published/ipcc_2001/text.pdf

The percentage of the above that can be assigned directly to mollusks
is not stated.

Reduction of CO2 is accomplished by the other two carbon "pumps".

hlabadie-ga

Hi knowitall22,

Well, an interesting question but not one that lends itself to an easy
answer.

We couldn't find reference to molluscs in particular, most of the
information pertains to all calcium carbonate building organisms (for
example, foramaniferans) but you may find this information on the
carbon cycles helpful in your search for the answer. You'll find that
approximately 50 billion tons of carbon (183 billion tons of carbon
dioxide*) enters the water from the atmosphere. The organisms that use
the carbon dioxide, give off about 40 billion tons carbon (146 billion
tons of carbon dioxide) through their metabolism, which is a net
uptake of 10 billion tons by ocean life. After the organisms die, the
calcium carbonate of their shells continue to exist. Part of the
calcium carbonate disolves back into the water and the rest
precipitate to the ocean floor where it becomes part of ocean
sediments. The net rate at which this occurs is .2 billion tons of
carbon per year (.73 billion tons of carbon dioxide). So, if you are
asking what the net removal of carbon dioxide from the atmospheric
sink is through biological processes in the ocean into the sedimentary
sink, the answer would be .73 billion tons of carbon dioxide. But keep
in mind that eventually the calcium carbonate will again become part
of the atomosphere through the weathering of limestone and volcanic
activity.

*The equivilent weight of carbon in carbon dioxide can be calculated
by multiplying the weight in carbon by the molecular weight of carbon
dioxide divided by the molecular weight of carbon, so the weight in
carbon multiplied by
[16 + 2 x 12] / 12 = the equivilent weight in carbon dioxide. 


Additional Links:

The Carbon Cycle:
http://www.geog.ouc.bc.ca/physgeog/contents/9r.html

noaa research: see figure one:
http://www.oar.noaa.gov/spotlite/archive/spot_carbon.html

I hope this helps - I would be happy to post this as an answer if you
are satisfied with the information, let me know.

Sincerely,
hummer

Search Strategy:
None. My son, a university wildlife biology student, is home for the
holidays and took a special interest in your question.

Hummer-ga
  Resubmit your comment of 12/27/02 to  question ID133321 as an answer
and I will accept it as an answer, for which you may collect the fee.
Thanks,
knowitall22-ga