sinking particles. With each trophic transfer, a
percentage (50–70%) of the organic carbon is
respired, so only a small fraction of the original
primary production forms sinking particles.
Although picoplankton may dominate primary
production in oceanic systems, their production is
considered ‘regenerative’ and contributes little to
the production of sinking material. Alternatively,
production by larger phytoplankton such as
diatoms (>20 mm in size) may represent a smaller
fraction of primary production, but their
contribution to the biological pump is larger
because fewer trophic steps are taken to produce
sinking particles.
The Carbonate Pump
A process considered part of the biological pump
(depending how it is defined) is the formation and
sinking of calcareous skeletal material by some
marine phytoplankton (e.g., coccolithophores) and
animals (e.g., pteropods and foraminifera). Calcification is the process by which marine organisms
combine calcium with carbonate ions to form hard
body parts. The resulting calcium carbonate
(CaCO 3 ) is dense and sinks out of the surface water
with export production (Figure 8). The global mean
ratio for carbon sinking from the surface ocean as
CaCO 3 or organic carbon is 1:4. However, unlike
organic matter, CaCO 3 is not remineralized as it
sinks; it only begins to dissolve in intermediate and
deep waters, waters undersaturated with respect to
CaCO 3 . Complete dissolution of CaCO 3 skeletons
typically occurs at depths of 1–4 km (in the north
Pacific Ocean) to 5 km (in the North Atlantic). This
depth zone is known as the carbonate compensation
depth. CaCO 3 is only found in sediments shallower
than the carbonate compensation depth. Globally,
the CO 2 sink in sedimentary rock is four times
greater than the sink in organic sediments.
Summary
In summary, the biological and physical processes of
the oceanic carbon cycle play an important role in
the regulation of atmospheric CO 2 . However, the
intricacies of the oceanic carbon cycle are vast and
continued ocean research is essential to better
understand the controls of the Earth’s climate.
See also
Atmospheric Input of Pollutants. Carbon Dioxide
(CO 2 ) Cycle.
Further Reading
Bates NR, Michaels AF, and Knap AH (1996) Seasonal and
interannual variability of oceanic carbon dioxide
species at the U.S. JGOFS Bermuda Atlantic Time-series
Study (BATS) site. Deep-Sea Research II 43: 347--383.
Bolin B (ed.) (1983) The Major Biogeochemical Cycles and
Their Interactions: SCOPE 21. New York: Wiley.
Carlson CA, Ducklow HW, and Michaels AF (1994)
Annual flux of dissolved organic carbon from the
euphotic zone in the northwestern Sargasso Sea. Nature
371: 405--408.
Denman K, Hofman H, and Marchant H (1996) Marine
biotic responses to environmental change and feedbacks
to climate. In: Houghton JT, Meira Filho LG, and
Callander BA, et al. (eds.) Climate Change 1995: The
Science of Climate Change. New York: Cambridge
University Press.
Follows MJ, Williams RG, and Marshall JC (1996) The
solubility pump of carbon in the subtropical gyre of the
North Atlantic. Journal of Marine Research 54:
605--630.
Hansell DA and Carlson CA (1998) Net community
production of dissolved organic carbon. Global
Biogeochemical Cycles 12: 443--453.
Holme ´n K (1992) The global carbon cycle. In: Butcher SS,
Charlson RJ, Orians GH, and Wolfe GV (eds.) Global
Biogeochemical Cycles, pp. 239--262. New York:
Academic Press.
Houghton JT, Meira Filho LG, and Callander BA, et al.
(eds.) (1996) Climate Change 1995: The Science of
Climate Change. New York: Cambridge University
Press.
Michaels AF and Silver MW (1988) Primary producers,
sinking fluxes and the microbial food web. Deep-Sea
Research 35: 473--490.
Sarmiento JL and Wofsy (eds.) (1999) A U.S. Carbon Cycle
Science Plan. Washington, DC: U.S. Global Change
Research Program.
Sarmiento JL, Hughes TMC, Stouffer RJ, and Manabe S
(1998) Simulated response of the ocean carbon cycle to
anthropogenic climate warming. Nature 393: 245--249.
Schlesinger WH (1997) Biogeochemistry: An Analysis of
Global Change. New York: Academic Press.
Siegenthaler U and Sarmiento JL (1993) Atmospheric
carbon dioxide and the ocean. Nature 365: 119--125.
Steinberg DK, Carlson CA, Bates NR, Goldthwait SA,
Madin LP, and Michaels AF (2000) Zooplankton
vertical migration and the active transport of dissolved
organic and inorganic carbon in the Sargasso Sea. DeepSea Research I 47: 137--158.
Takahashi T, Tans PP, and Fung I (1992) Balancing the
budget: carbon dioxide sources and sinks, and the effect
of industry. Oceanus 35: 18--28.
Varney M (1996) The marine carbonate system.
In: Summerhayes CP and Thorpe SA (eds.)
Oceanography an Illustrated Guide, pp. 182--194.
London: Manson Publishing.
504 CARBON CYCLE
percentage (50–70%) of the organic carbon is
respired, so only a small fraction of the original
primary production forms sinking particles.
Although picoplankton may dominate primary
production in oceanic systems, their production is
considered ‘regenerative’ and contributes little to
the production of sinking material. Alternatively,
production by larger phytoplankton such as
diatoms (>20 mm in size) may represent a smaller
fraction of primary production, but their
contribution to the biological pump is larger
because fewer trophic steps are taken to produce
sinking particles.
The Carbonate Pump
A process considered part of the biological pump
(depending how it is defined) is the formation and
sinking of calcareous skeletal material by some
marine phytoplankton (e.g., coccolithophores) and
animals (e.g., pteropods and foraminifera). Calcification is the process by which marine organisms
combine calcium with carbonate ions to form hard
body parts. The resulting calcium carbonate
(CaCO 3 ) is dense and sinks out of the surface water
with export production (Figure 8). The global mean
ratio for carbon sinking from the surface ocean as
CaCO 3 or organic carbon is 1:4. However, unlike
organic matter, CaCO 3 is not remineralized as it
sinks; it only begins to dissolve in intermediate and
deep waters, waters undersaturated with respect to
CaCO 3 . Complete dissolution of CaCO 3 skeletons
typically occurs at depths of 1–4 km (in the north
Pacific Ocean) to 5 km (in the North Atlantic). This
depth zone is known as the carbonate compensation
depth. CaCO 3 is only found in sediments shallower
than the carbonate compensation depth. Globally,
the CO 2 sink in sedimentary rock is four times
greater than the sink in organic sediments.
Summary
In summary, the biological and physical processes of
the oceanic carbon cycle play an important role in
the regulation of atmospheric CO 2 . However, the
intricacies of the oceanic carbon cycle are vast and
continued ocean research is essential to better
understand the controls of the Earth’s climate.
See also
Atmospheric Input of Pollutants. Carbon Dioxide
(CO 2 ) Cycle.
Further Reading
Bates NR, Michaels AF, and Knap AH (1996) Seasonal and
interannual variability of oceanic carbon dioxide
species at the U.S. JGOFS Bermuda Atlantic Time-series
Study (BATS) site. Deep-Sea Research II 43: 347--383.
Bolin B (ed.) (1983) The Major Biogeochemical Cycles and
Their Interactions: SCOPE 21. New York: Wiley.
Carlson CA, Ducklow HW, and Michaels AF (1994)
Annual flux of dissolved organic carbon from the
euphotic zone in the northwestern Sargasso Sea. Nature
371: 405--408.
Denman K, Hofman H, and Marchant H (1996) Marine
biotic responses to environmental change and feedbacks
to climate. In: Houghton JT, Meira Filho LG, and
Callander BA, et al. (eds.) Climate Change 1995: The
Science of Climate Change. New York: Cambridge
University Press.
Follows MJ, Williams RG, and Marshall JC (1996) The
solubility pump of carbon in the subtropical gyre of the
North Atlantic. Journal of Marine Research 54:
605--630.
Hansell DA and Carlson CA (1998) Net community
production of dissolved organic carbon. Global
Biogeochemical Cycles 12: 443--453.
Holme ´n K (1992) The global carbon cycle. In: Butcher SS,
Charlson RJ, Orians GH, and Wolfe GV (eds.) Global
Biogeochemical Cycles, pp. 239--262. New York:
Academic Press.
Houghton JT, Meira Filho LG, and Callander BA, et al.
(eds.) (1996) Climate Change 1995: The Science of
Climate Change. New York: Cambridge University
Press.
Michaels AF and Silver MW (1988) Primary producers,
sinking fluxes and the microbial food web. Deep-Sea
Research 35: 473--490.
Sarmiento JL and Wofsy (eds.) (1999) A U.S. Carbon Cycle
Science Plan. Washington, DC: U.S. Global Change
Research Program.
Sarmiento JL, Hughes TMC, Stouffer RJ, and Manabe S
(1998) Simulated response of the ocean carbon cycle to
anthropogenic climate warming. Nature 393: 245--249.
Schlesinger WH (1997) Biogeochemistry: An Analysis of
Global Change. New York: Academic Press.
Siegenthaler U and Sarmiento JL (1993) Atmospheric
carbon dioxide and the ocean. Nature 365: 119--125.
Steinberg DK, Carlson CA, Bates NR, Goldthwait SA,
Madin LP, and Michaels AF (2000) Zooplankton
vertical migration and the active transport of dissolved
organic and inorganic carbon in the Sargasso Sea. DeepSea Research I 47: 137--158.
Takahashi T, Tans PP, and Fung I (1992) Balancing the
budget: carbon dioxide sources and sinks, and the effect
of industry. Oceanus 35: 18--28.
Varney M (1996) The marine carbonate system.
In: Summerhayes CP and Thorpe SA (eds.)
Oceanography an Illustrated Guide, pp. 182--194.
London: Manson Publishing.
504 CARBON CYCLE