sedimentation (intraclastic breccia), or collapse of rock
material (solution and collapse breccias). Solution and
collapse breccias are common in karst settings such as
Florida where sinkholes and other types of karst features
form. Also common in Pleistocene and Holocene limestones throughout the Florida-Caribbean region are
multihued blackened limestone pebbles in a calcrete
matrix (Figure 1a and b). Simple laboratory (heating)
experiments and observations (campfire sites) have shown
that pebbles of limestone (coral, mollusc, grainstone, and
calcrete) can blacken almost instantaneously when heated
to between 400
and 500
C (Shinn and Lidz, 1988). Being
the lightning capital of the U.S., Florida has, and has had
in the geological past, no shortage of sources of ignition
for lighting of natural forest fires.
Bibliography
Enos, P., and Perkins, R. D., 1977. Quaternary Sedimentation in
South Florida. Tulsa, OK: Geological Society of America
Memoir 147.
Harrison, R. S., and Steinen, R. P., 1978. Subaerial crusts, caliche
profiles, and breccia horizons: comparison of some Holocene
and Mississippian exposure surfaces, Barbados and Kentucky.
Geological Society of America Bulletin, 89, 385–396.
Kahle, C. F., 1978. Subaerial Exposure of Silurian Shelf-Margin
Reefs. Oklahoma City, OK: Northwestern Ohio: AAPG-SEPM
Annual Meeting Program (Abs), p. 79.
Multer, H. G., and Hoffmeister, J. E., 1968. Subaerial laminated
crusts of the Florida Keys. Geological Society of America
Bulletin, 79, 183–192.
Robbin, D. M., 1981. Subaerial CaCO 3 crust: a tool for timing reef
initiation and defining sea level changes. In Proceedings International Coral Reef Symposium, 4th, Manila, Philippines, 1,
575–579.
Robbin, D. M., and Stipp, J. J., 1979. Depositional rate of laminated
soilstone crusts, Florida Keys. Journal of Sedimentary Petrology, 49(1), 175–180.
Shinn, E. A., and Lidz, B. H., 1988. Blackened limestone
pebbles: fire at subaerial unconformities. In James, N. P., and
Choquette, P. W. (eds.), Paleokarst. New York: Springer, pp.
117–131.
Swett, K., 1974. Calcrete crusts in an Arctic permafrost environment: American Journal of Science, 274, 1059–1063.
Cross-references
Florida Keys
Last Glacial Lowstand and Shelf Exposure
Porosity Variability In Limestone Sequences
Reef Drilling
CARBON FLUXES OF CORAL REEFS
Marlin J. Atkinson
Hawaii Institute of Marine Biology, Kaneohe, Hawaii
Synonyms
Carbon dynamics
Definition
The carbon fluxes of coral reefs are the rates of carbon
exchange between sea water and reef organisms, communities, and habitats. They characterize key biochemical
processes such as photosynthesis, respiration, and calcification, as well as important biogeochemical transformations such as diagenesis and dissolution. Fluxes are
reported as rates of exchange per area.
Introduction
A coral reef is a living structure that maintains itself at sea
level by the combined biogenic calcification of a variety of
taxa. A healthy, sustainable coral reef ecosystem is comprised of diverse communities that capture and utilize
energy from sunlight, waves, and organic particles. The
motivation for studying carbon fluxes of coral reefs is to
delineate and characterize these rates of energy transfer
in order to compare reefs with other ecosystems and to
compare among reefs, and to predict responses of reefs
to natural or anthropogenic perturbations.
Specific communities within a coral reef ecosystem
achieve high rates of photosynthesis and, consequently,
production of organic carbon. Over the past 80 years,
a variety of ideas have been advanced to explain these
high rates of carbon production. One prevalent view is that
close physical and ecological relationships between autotrophs (organisms such as plants that produce organic carbon from inorganic carbon) and heterotrophs (organisms
that consume organic carbon, i.e., most animals) create
an ecosystem where plant nutrients (compounds of nitrogen, phosphorus, sulfur, etc.) are either retained within
the biota or recycled within the community, maximizing
carbon production. A more recent view is that coral reefs
produce organic carbon that is low in nutrients and is
quickly respired. This article provides an overview of the
carbon dynamics or carbon fluxes of coral reefs.
Fluxes of dissolved inorganic carbon
The amount of carbon, in both dissolved and particulate
forms, is orders of magnitude lower in the water column
above a coral reef than it is in the biota or in the sediments
(Table 1). Dissolved inorganic carbon (in the form of
dissolved carbon dioxide and carbonate and bi-carbonate
ions) is removed from the water column by autotrophs
and converted to, or “fixed” into, both organic compounds
(tissue and dissolved organic compounds) and inorganic
compounds (notably calcium carbonate skeletons of
marine algae and corals; Kinsey, 1985; Hatcher, 1997;
Gattuso et al., 1998; Atkinson and Falter, 2003). The total
amount of carbon fixed into organic matter per day is
termed gross primary production. Gross primary production is typically estimated by adding daytime net photosynthesis to the 24-h respiration rate, based on dark
respiration. Light respiration can be up to two times
greater than dark respiration. Published values of gross
primary production that assume light respiration equals
dark respiration are therefore of questionable accuracy
CARBON FLUXES OF CORAL REEFS
181
material (solution and collapse breccias). Solution and
collapse breccias are common in karst settings such as
Florida where sinkholes and other types of karst features
form. Also common in Pleistocene and Holocene limestones throughout the Florida-Caribbean region are
multihued blackened limestone pebbles in a calcrete
matrix (Figure 1a and b). Simple laboratory (heating)
experiments and observations (campfire sites) have shown
that pebbles of limestone (coral, mollusc, grainstone, and
calcrete) can blacken almost instantaneously when heated
to between 400
and 500
C (Shinn and Lidz, 1988). Being
the lightning capital of the U.S., Florida has, and has had
in the geological past, no shortage of sources of ignition
for lighting of natural forest fires.
Bibliography
Enos, P., and Perkins, R. D., 1977. Quaternary Sedimentation in
South Florida. Tulsa, OK: Geological Society of America
Memoir 147.
Harrison, R. S., and Steinen, R. P., 1978. Subaerial crusts, caliche
profiles, and breccia horizons: comparison of some Holocene
and Mississippian exposure surfaces, Barbados and Kentucky.
Geological Society of America Bulletin, 89, 385–396.
Kahle, C. F., 1978. Subaerial Exposure of Silurian Shelf-Margin
Reefs. Oklahoma City, OK: Northwestern Ohio: AAPG-SEPM
Annual Meeting Program (Abs), p. 79.
Multer, H. G., and Hoffmeister, J. E., 1968. Subaerial laminated
crusts of the Florida Keys. Geological Society of America
Bulletin, 79, 183–192.
Robbin, D. M., 1981. Subaerial CaCO 3 crust: a tool for timing reef
initiation and defining sea level changes. In Proceedings International Coral Reef Symposium, 4th, Manila, Philippines, 1,
575–579.
Robbin, D. M., and Stipp, J. J., 1979. Depositional rate of laminated
soilstone crusts, Florida Keys. Journal of Sedimentary Petrology, 49(1), 175–180.
Shinn, E. A., and Lidz, B. H., 1988. Blackened limestone
pebbles: fire at subaerial unconformities. In James, N. P., and
Choquette, P. W. (eds.), Paleokarst. New York: Springer, pp.
117–131.
Swett, K., 1974. Calcrete crusts in an Arctic permafrost environment: American Journal of Science, 274, 1059–1063.
Cross-references
Florida Keys
Last Glacial Lowstand and Shelf Exposure
Porosity Variability In Limestone Sequences
Reef Drilling
CARBON FLUXES OF CORAL REEFS
Marlin J. Atkinson
Hawaii Institute of Marine Biology, Kaneohe, Hawaii
Synonyms
Carbon dynamics
Definition
The carbon fluxes of coral reefs are the rates of carbon
exchange between sea water and reef organisms, communities, and habitats. They characterize key biochemical
processes such as photosynthesis, respiration, and calcification, as well as important biogeochemical transformations such as diagenesis and dissolution. Fluxes are
reported as rates of exchange per area.
Introduction
A coral reef is a living structure that maintains itself at sea
level by the combined biogenic calcification of a variety of
taxa. A healthy, sustainable coral reef ecosystem is comprised of diverse communities that capture and utilize
energy from sunlight, waves, and organic particles. The
motivation for studying carbon fluxes of coral reefs is to
delineate and characterize these rates of energy transfer
in order to compare reefs with other ecosystems and to
compare among reefs, and to predict responses of reefs
to natural or anthropogenic perturbations.
Specific communities within a coral reef ecosystem
achieve high rates of photosynthesis and, consequently,
production of organic carbon. Over the past 80 years,
a variety of ideas have been advanced to explain these
high rates of carbon production. One prevalent view is that
close physical and ecological relationships between autotrophs (organisms such as plants that produce organic carbon from inorganic carbon) and heterotrophs (organisms
that consume organic carbon, i.e., most animals) create
an ecosystem where plant nutrients (compounds of nitrogen, phosphorus, sulfur, etc.) are either retained within
the biota or recycled within the community, maximizing
carbon production. A more recent view is that coral reefs
produce organic carbon that is low in nutrients and is
quickly respired. This article provides an overview of the
carbon dynamics or carbon fluxes of coral reefs.
Fluxes of dissolved inorganic carbon
The amount of carbon, in both dissolved and particulate
forms, is orders of magnitude lower in the water column
above a coral reef than it is in the biota or in the sediments
(Table 1). Dissolved inorganic carbon (in the form of
dissolved carbon dioxide and carbonate and bi-carbonate
ions) is removed from the water column by autotrophs
and converted to, or “fixed” into, both organic compounds
(tissue and dissolved organic compounds) and inorganic
compounds (notably calcium carbonate skeletons of
marine algae and corals; Kinsey, 1985; Hatcher, 1997;
Gattuso et al., 1998; Atkinson and Falter, 2003). The total
amount of carbon fixed into organic matter per day is
termed gross primary production. Gross primary production is typically estimated by adding daytime net photosynthesis to the 24-h respiration rate, based on dark
respiration. Light respiration can be up to two times
greater than dark respiration. Published values of gross
primary production that assume light respiration equals
dark respiration are therefore of questionable accuracy
CARBON FLUXES OF CORAL REEFS
181