Coral Reefs and the Carbon Cycle

1
Coral Reefsand the Carbon Cycle
NOAA
Background on Reefs and Carbon More than
Reefs? Reef CaCO3 Production Accumulation Contro
ls on Reef Calcification
Joanie Kleypas National Center for
Atmospheric Research
2
Conclusions

• Coral reef systems are not big players in the
  organic component of the C-cycle, but ARE in
  terms of CaCO3
• Other shelf ecosystems may be important in
  accumulation of CaCO3 but their budgets are
  poorly constrained
• Coral reef CaCO3 production appears to have
  declined after sea level stabilized
• This may be a natural process related to reef
  succession change in morphology or community
  structure

3
Coral Reefsand the Carbon Cycle
NOAA
Background on Reefs and Carbon More than
Reefs? Reef CaCO3 Production Accumulation Contro
ls on Reef Calcification
4
Coral Reefs- Organic Carbon Production -

• Organic Carbon Production in Low Nutrient Waters
• High organic production (79584 g C m2 y1)
• Topographically induced upwelling, internal tidal
  bores endo-upwelling
• Efficient production of organic carbon (Nitrogen
  fixation)
• C N P
• Coral reefs 550301
• Open ocean 106161

Smith, 1988
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Coral Reefs- Organic Carbon Production
-(Gattuso, Frankignoulle, Wollast 1998)
Pg/R Reef Flats 1.07
0.1 (n43) Reef System 1.28 0.2 (n9)
Respiration
Gross Production
Organic C metabolism of coral reefs is
balanced or slightly autotrophic
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Coastal Ecosystems - Organic Carbon Production
-(Gattuso, Frankignoulle, Wollast 1998)
Gross Prod. mol C m2 y1 Area 106 km2 NEP Tmol C y1
Estuaries 22 1.4 -8
Macrophyte-dominated 87 2.0 37
Coral Reefs 144 0.6 6
Salt marshes 185 0.4 7
Mangroves 232 0.2 18
Remaining shelf 18 21.4 171
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Coastal Ecosystems - Organic Carbon Production
-(Gattuso, Frankignoulle, Wollast 1998)
Gross Prod. mol C m2 y1 Area 106 km2 NEP Tmol C y1
Estuaries 22 1.4 -8
Macrophyte-dominated 87 2.0 37
Coral Reefs 144 0.6 6
Salt marshes 185 0.4 7
Mangroves 232 0.2 18
Remaining shelf 18 21.4 171
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Coral Reefs - Inorganic Carbon Production -
(Milliman 1993 Milliman Droxler 1996)
Habitat Area CaCO3 CaCO3 CaCO3 flux
glob. prod. accum. x106 km2 g/m2/y 1012
mol/y 1012 mol/y reefs 0.6 1500 9
7 banks 0.8 500 4 2
carbonate 10.0 20-100 6
3 shelves open ocean 290.0 20 60 11
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Coral ReefHypothesis
Changes in basin-shelf partitioning of CaCO3
production caused glacial-interglacial
fluctuations in atmospheric CO2
Berger 1982 Opdyke Walker 1992 Walker
Opdyke 1995 Kleypas 1997 ? shelf flooding
initiated pulse in CaCO3 but not until 8000
yBP Archer et al. 2000 ? can explain portion
but not all of post-glacial CO2 rise Ridgwell
Kennedy 2004 ? 20 ppm CO2 increase in late
Holocene
Ridgwell and Kennedy 2004
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Estimates of Shelf CaCO3 Flux
Flux Rate g m-2 y-1 Area 106 km2 Accumulation 1012 mol y-1
Turekian 1965 negligible NA NA
Garrels Mackenzie 1971 negligible NA NA
Chave 1972 1,000-20,000 NA NA
Milliman 1974 350 1.4 5
Smith 1978 1,000 0.6 6
Schlager 1981 1,450 0.6 8.1
Kinsey Hopley 1991 1,812 0.6 11
Milliman Droxler 1996 1,500 0.6 7
Kleypas 1997 light-dependent 0.6-0.9 9-10
Opdyke Schimel 2000 1,600 0.8 14-20
Reef environments only
Modified from Opdyke Schimel 2000
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600,000 km2
Smiths (1978) reef area estimate

• Smith Kinseys (1976) avg calcn rate
• 20 reefs _at_ 4000 g m-2 y-1
• 80 lagoons _at_ 800 g m-2 y-1

1500 g m-2 y-1
0.9 x 109 tons CaCO3 y-1
Net CaCO3 production
10 dissolved/exported 10 biological
erosion/corrosion
20
0.7 x 109 tons CaCO3 y-1
Net CaCO3 accumulation
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Coral Reefsand the Carbon Cycle
NOAA
Background on Reefs and Carbon More than
Reefs? CaCO3 Production Accumulation Controls
on Reef Calcification
13
How Good are Estimates of Shelf Accumulation?

• Coral reefs are the gold standard of high
  carbonate production
• Almost all estimates of shelf carbonate
  production have concentrated on coral reefs

cold water corals may cover as large an area
as warm-water corals that form shallow reefs
(Williams et al., Eos 21 Nov 2006)
The mean annual calcification of L. corallioides
populations are similar to those reported for
tropical coralline algae (Martin et al. 2006)
These production and accumulation rates are
similar to the lower end of such rates from
tropical coral reef environments (Bosence and
Wilson 2003)
14
How Good are Estimates of Shelf Accumulation?

• What about non-tropical carbonates?
• Milliman Droxler 1996 estimated that for
  non-tropical shelves
• calcification rates lt 20 of tropical carbonates
• net accumulation 30 of tropical
  carbonates

These data are even less constrained than for
reefs
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Types of Shallow Water Carbonates

• System
• Coral Reefs
• Halimeda banks
• Coralline algae rhodolith beds
• Cold-water reefs
• Cool-water carbonates
• Ooid shoals
• Oyster banks
• . etc

Organism Corals Calcareous algae Coralline red
algae Green algae Halimeda/Penicillus Forams Spong
es Bryozoans Brachiopods Molluscs Annelids Echinod
erms Arthropods
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Calcification Rates of Benthic Calcifiers
Calcifier Organism G g m-2 y-1 Reference
Corals Porites sp. Skel. ext. x dens. (per surf. area of coral) 5,000-28,000 Lough Barnes 2000 (Indo-Pacific)
Annelids (HMC) 11,000 2-11,836 Smith et al. 2005 (NZ) Medernach et al. 2000 (Mediterranean)
Coralline algae In situ incubations L. corallioides In situ chambers Maerl (Norway) Maerl (NW France) Maerl (W Ireland) 1,500-10,300 300-3,000 895-1,423 876 30-250 Chisholm 2000 (Lizard Is. GBR) Martin et al 2006 Boscence Wilson 2003
Halimeda Standing stock x turnover rate 2,234 1000-3000 Drew 1983
Benthic forams Reef forams Cold-water forams 2000 480 30-230 0.326 Hallock 1981 (Indo-Pacific) Yamano et al. 2000 (Green I) Langer et al. 1997 Wisshak Ruggeberg 2006 (Baltic)
Bryozoans Pentapora fascialis larger bryozoans Cellaria sinuosa thickets 358-1,214 24-240 12-57 Cocito Ferdeqhini 2001 (NW Med.) Smith Nelson 1994 Bader Schafer 2005 (British Channel)
Echinoderms Ophiothrix fragilis 682 Migne et al. 1998 (Dover Strait)
Molluscs Potamocorbula amurensis (clam) 221 (/-184) Chauvaud et al. 2003 (San Francisco)
PHOTOTROPHIC
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Recent discoveries Rhodoliths / Maerl Beds
In high latitudes, usually clear water In
tropics/ subtropics, where coral reefs are
unsuccessful
Foster 2001
McCalester
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Bosence Wilson 2003 (NE Atlantic Maerl Beds)
Production g CaCO3 m2 y1 Accumulation (m ky1)
W Ireland 30-250
NW France 876
Norway 895-1,423
Norway 0.8-1.4
Orkney 0.08
Cornwall 0.5
tropical coralline algae 1,500-10,300
Corals 5,000-28,000 0.12-1.80

• These production and accumulation rates are
  similar to the lower end of such rates from
  tropical coral reef environments. This is
  achieved by high standing crops that compensate
  for the lower growth rates of the temperate
  algae.

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Recent discoveries Cold-water corals(not
quite shelf deposition)
Challenger Mound Eos, 21 Nov 2006 Trevor
Williams and 29 others Mounds 600-900 m
depths Up to 155 m accumulation over 2 MY (10 m
per glacial cycle)
Roberts et al. Science 2006
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Coral Reefsand the Carbon Cycle
AIMS
Background on Reefs and Carbon More than
Reefs? Reef CaCO3 Production Accumulation Contro
ls on Reef Calcification
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Budget for Reef Greef Dreef Tr (net
Gshelf gt Greef) Budget for C-Cycle Gshelf
Dshelf
G Community calcification inorganic
cementation ()
D Dissolution ()
Tr Transport on/off reef ( or usually )
Rates vary with T, O, light,
Rates vary with T, O, bioerosion
Rates vary with framework versus sediments,
hydrodynamic regime, shelf morphology,
Export limits reef development without
necessarily affecting carbon cycle.
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Calcification Measurements(not always the same
thing)
Technique Measures Timescale
Skeletal incorporation of radioisotopes 45Ca, 14C Gskel Dskel Minutes to hours
Buoyant weight Gskel Dskel Duration of experiment
?Alk of monoculture or ?pH-?O2 Gskel Dskel Discrete measurements over duration of experiment
Coral band increment Gskel Dskel Ginorg Integrated over time of band formation post-depositional cementation
Growth rate x standing stock Usually generation time/turnover rate of organism
?Alk of closed system Gsys Dsys Gsys Discrete measurements over duration of experiment
?Alk in open system Gsys Dsys mixing Discrete measurements over duration of experiment requires knowledge of mixing regime
Sedimentological (thickness x density) /time Gsys Dsys transport Months to gt millenia
Organisms Communities
Systems
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Alkalinity Anomaly
Net organism calcification
Net organism calcification
Photo/Resp.
Calcification
Exchange with the ocean
Inputs from land
Inorganic Cementation
Dissolution
Sediment Volume
Organic Matter Resp.
Net reef accumulation
?
Inorganic Cementation
Dissolution
Dissolution
Bioerosion
export
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Photo/Resp.
Net organism calcification
0.8-1.5 g cm2 y-1
Calcification
Inorganic Cementation
Dissolution
Net community calcification
0.1-1.3 g cm2 y-1
Net reef accumulation
0.75-0.90 g cm2 y-1
Bioerosion
0.1-0.5 g cm2 y-1
0.004-0.07 g cm2 y-1
Dissolution
export
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A High Preservation Rate?

• Reef accumulation rates indicate
• very little carbonate loss
• ... OR
• todays calcification rates are lower than in the
  past
• Coral reefs have declined from anthropogenic
  stress in the last century, but coral reef
  calcification has probably been declining for
  thousands of years.

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Changes in Reef CaCO3 Accumulation Over
Time(Wistari Reef, Australia)
Average Holocene Accumulation
2 4 6 8 10
Accum. Rate g cm-2 y-1
Accumulation History
10 9 8 7 6 5 4
3 2 1 0
103 Years Before Present
Ryan et al. 2001
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Post-glacial Reef Deposition
5000 ybp
5000 ybp
3000 ybp
TR?
7000 ybp
8000 ybp
9000 ybp
Reef growth progressively limits hydrographic
exchange and residence time increases
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Saturation State Changes with Residence
TimeBroecker Takahashi 1966
Bahamas Bank
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G (kg m-2 y-1)
5.5
Calcification Rates versus Residence Time Demicco
Hardie 2002
0.0
G ƒ(z,Tr) Carbonate production is favored at
edges of the platform and slows down dramatically
beyond 20 m of edge.
200
Tr (days)
0
Demicco Hardie, J. Sed Res. 2002
30
Growth forms can affect production and
accumulation rates per m2
NOAA
7,000 g m-2 y-1
Did the emergence of Acropora accelerate
carbonate production?
18,300 g m-2 y-1
31
Model of Reef Growth versus Sea Level Rise
drowned/ sediment
massive
branching 1
branching 2
120 m
seafloor
32
Coral Reefsand the Carbon Cycle
NOAA
Background on Reefs and Carbon More than
Reefs? Reef CaCO3 Production Accumulation Contro
ls on Reef Calcification
33
Physical Variables that Affect Calcification

• Temperature Latitude
• Saturation State Latitude
• Irradiance Depth, Latitude

T
O
34
Between Equator and 30º is a 5x decrease in
Porites calcification rate Saturation state is a
factor, but SST and light probably are as well
Darwin Point Clue 1 reef-building at higher
latitudes occurs in very clear waters Clue 2
reef depth shallows at higher latitude
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The basic calculation Light-based calcification
calculated on an hourly basis for a full year and
total calcification over the entire depth of the
reef is summed.
36
Zmax log(Imin/Isurf) K490
G Gmax tanh Iz/Ik
Iz typically 2000 µEins m-2 s-1 Ik 250-300 µEins
m-2 s-1 light is not limiting at surface
37
LightOnly
clear
murky