# Presentation: 647707

## Coral Reefsand the Carbon Cycle

**Coral Reefs****and the Carbon Cycle**

**   ****Joanie Kleypas**
**   ****National Center for **
**   ****Atmospheric Research**

***NOAA***

**Background on Reefs and Carbon**
**More than Reefs?**
**Reef CaCO****3**** Production & Accumulation**
**Controls on Reef Calcification**

**Notes:**
Two Main points

How well can we quantify shelf calcification?
What controls shallow benthic calcification?

Justification:  shallow benthic calcification affects the carbon cycle

## Conclusions

**Conclusions**

**Coral reef systems are not big players in the organic component of the C-cycle, but ARE in terms of CaCO****3**
**Other shelf ecosystems may be important in accumulation of CaCO****3**** but their budgets are poorly constrained**
**Coral reef CaCO****3**** 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**

## Coral Reefsand the Carbon Cycle

**Coral Reefs****and the Carbon Cycle**

***NOAA***

**Background on Reefs and Carbon**
**More than Reefs?**
**Reef CaCO****3**** Production & Accumulation**
**Controls on Reef Calcification**

**Notes:**
Two Main points

How well can we quantify shelf calcification?
What controls shallow benthic calcification?

Justification:  shallow benthic calcification affects the carbon cycle

## Coral Reefs- Organic Carbon Production -

**Organic Carbon Production in Low Nutrient Waters**
**High organic production (79****–****584 g C m****–****2**** y****–****1****)**
**Topographically induced upwelling, internal tidal bores; ‘endo-upwelling’**
**Efficient production of organic carbon (**Nitrogen fixation)
**	****	****	****  ****	****	****  ****C : ****N**** : ****P**** **
**	****Coral reefs:  ****	****550:****30****:****1**** **
**	****Open ocean:****	****106:****16****:****1**

***Smith, 1988***

**Notes:**
does not seem to be sustained by the same nutrient source as the surrounding ocean (advective inputs from below) due to physical limitation, although active upwelling along the slope (e.g. 151) and internal tidal bores (83) can sometimes provide a significant nutrient supply.

Smith (129) offered two alternative explanations. 
First, the C:N:P ratio of reef benthic plants (550:30:1; Ref. 7) is much higher than the typical Redfield ratio (106:16:1). Therefore, the production of organic carbon is much more efficient in reef systems per unit of nitrogen and phosphorus. 
Second, oceanic water impinging reefs is typically depleted in nitrogen relative to phosphorus. The well-established capacity of several reef organisms and physiographic zones to fix nitrogen enables reef communities to overcome nitrogen limitation.

## Coral Reefs- Organic Carbon Production -(Gattuso, Frankignoulle, Wollast 1998)

**Gross Production**

**Respiration**

**	****	****Pg/R**
**Reef Flats:        1.07 ± 0.1**
**(n=43)**
**Reef System:   1.28 ± 0.2**
**(n=9)**
**  **

**Organic C metabolism of coral reefs is balanced**
**or slightly autotrophic**

**Coral Reefs****- Organic Carbon Production -*****(Gattuso, Frankignoulle, Wollast 1998)***

**Notes:**
... but the carbon isn’t stored.

Gattuso, Frankignoulle and Wollast put together a nice review of carbonate production on continental shelves, and pulled together data from the few sites on coral reefs where production and respiration had been measured, and determined that for reef flats – the gross production to respiration ratio was near one.
For entire reef systems – and there are only 9 points here – the ratio is higher, but they concluded that organic carbonate metabolism of coral reefs is balanced or slightly autotrophic

## Coastal Ecosystems - Organic Carbon Production -(Gattuso, Frankignoulle, Wollast 1998)

|  | Gross Prod.
mol C m–2 y–1 | Area
106 km2 | NEP
Tmol C y–1 |
| --- | --- | --- | --- |
| 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 |

**Notes:**
In comparison to other shelf ecosystems, coral reefs do have high gross production, but the NET ECOSYSTEM PRODUCTION is small.

## Coastal Ecosystems - Organic Carbon Production -(Gattuso, Frankignoulle, Wollast 1998)

|  | Gross Prod.
mol C m–2 y–1 | Area
106 km2 | NEP
Tmol C y–1 |
| --- | --- | --- | --- |
| 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 |

## Coral Reefs - Inorganic Carbon Production - (Milliman 1993; Milliman & Droxler 1996)

**	****	****  ****flux             glob. prod.****	****accum.**
**	****x10****6**** km****2****	****g/m****2****/y****	****10****12 ****mol/y****	****10****12 ****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**

**Coral Reefs ****- Inorganic Carbon Production -**** *****(Milliman 1993; Milliman & Droxler 1996)***

**Notes:**
Where coral reefs DO MATTER to the carbon cycle is in their production of inorganic carbon.
These are the most widely quoted and used figures of carbonate production and accumulation in the oceans, by John Milliman.
What these numbers show is that:  Although shallow water environments comprise much less area than that of the open ocean, carbonate accumulation in these environments is equal to that of the open ocean.
Milliman was amazingly reasoned about estimating these values, but in reality, we don’t have much on the carbonate budgets of these carbonate environments.
NOTE THAT 11 x1012 moles CaCO3 is equivalent to 0.1 Pg C y-1

## Coral ReefHypothesis

**Berger 1982; Opdyke & Walker 1992; Walker & Opdyke 1995**
**Kleypas 1997 ****→ shelf flooding initiated pulse in CaCO****3**** but not until 8000 yBP**
**Archer *****et al*****. 2000 ****→ ****can explain portion – but not all – of post-glacial CO****2 ****rise**
**Ridgwell & Kennedy 2004 ****→**** 20 ppm CO****2**** increase in late Holocene**

***Ridgwell and Kennedy 2004***

***Changes in basin-shelf partitioning of CaCO******3****** production caused glacial-interglacial fluctuations in atmospheric CO******2***

**Notes:**
Increased CaCO3 buildup on continental shelves following post-glacial sea level rise accelerated atmospheric CO2 increase and deep ocean carbonate dissolution events.

Figure from Ridgwell, A. J., and M. J. Kennedy, Secular changes in the importance of neritic carbonate deposition as a control on the magnitude and stability of Neoproterozoic ice ages, in: The Extreme Proterozoic: Geology, Geochemistry, and Climate, Eds. Jenkins, G., et al., Geophysical Monograph Series Volume 146, American Geophysical Union, Washington DC (2004). 
4) In summary: The evolutionary success of planktic calcifiers during the Phanerozoic stabilized the climate system by introducing a new mechanism that acts to buffer ocean carbonate-ion concentration: the saturation-dependent preservation of carbonate in sea-floor sediments. Before this, buffering was primarily accomplished by adjustment of shallow-water carbonate deposition to balance oceanic inputs from weathering on land. Neoproterozoic ice ages of near-global extent and multimillion-year duration and the formation of distinctive sedimentary (cap) carbonates can thus be understood in terms of the greater sensitivity of the Precambrian carbon cycle to the loss of shallow-water environments and CO2-climate feedback on ice-sheet growth.

## 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***

**Notes:**
So one of the realizations is that estimates of tropical shelf carbonate production – particularly from reefs – have been increasing over time.

Another important point is  that measured rates of carbonate production from today’s reefs are probably lower than they were during the Holocene Transgression.  Calcification rates have probably been declining, particularly since sea level stabilized between 6000 and 3000 years ago.  A good example of this was the analysis of carbonate production versus carbonate accumulation at Wistari Reef.

Unfortunately, we don’t have a great idea of what really controls carbonate production rates.

## Smith & Kinsey’s (1976) avg calc’n rate:
20% reefs 	@ 4000 g m-2 y-1    
80% lagoons	@   800 g m-2 y-1

- 20% reefs 	@ 4000 g m-2 y-1
- 80% lagoons	@   800 g m-2 y-1

**1500 g m****-2**** y****-1**

**Net CaCO****3**** ****production**

**600,000 km****2**

- 10% dissolved/exported
- 10% biological erosion/“corrosion”

**Net CaCO****3**** accumulation**

**0.9 x 10****9**** tons CaCO****3**** y****-1**

**20%**

**0.7 x 10****9**** tons CaCO****3**** y****-1**

- Smith’s (1978) reef area estimate

**Notes:**
So these estimates are probably not all that accurate,
AND that is particularly true when we consider OTHER shelf carbonates

## Coral Reefsand the Carbon Cycle

**Coral Reefs****and the Carbon Cycle**

***NOAA***

**Background on Reefs and Carbon**
**More than Reefs?**
**CaCO****3**** Production & Accumulation**
**Controls on Reef Calcification**

## How Good are Estimates of Shelf Accumulation?

**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**

***“******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)**

**Notes:**
Note that there is some confusion about coral reefs – I think many estimates of coral reef calcification actually include other tropical calcifying environments – such as Halimeda beds, coralline algal banks etc.  

“These production and accumulation rates are similar to the lower end of such rates from tropical coral reef environments” (Bosence and Wilson 2003)
“The mean annual calcification of L. corallioides populations ... are similar to those reported for tropical coralline algae ...” (Martin et al. 2006)
Cold-water coral reefs

## What about non-tropical carbonates?

Milliman & Droxler 1996 estimated that for non-tropical shelves:

calcification rates < 20% of tropical carbonates

net accumulation  ~ 30% of tropical            carbonates

**Milliman & Droxler 1996 estimated that for *****non-tropical***** shelves:**
** **
**calcification rates < 20% of tropical carbonates**
**net accumulation  ~ 30% of tropical            carbonates**

**How Good are Estimates of Shelf Accumulation?**

**These data are even less**
**constrained than for reefs**

**Notes:**
Do we need to revise our estimates of shelf carbonate production and accumulation?

## 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**
**Sponges**
**Bryozoans**
**Brachiopods**
**Molluscs**
**Annelids**
**Echinoderms**
**Arthropods  **

**Notes:**
First, I’d like to revisit tropical shelf carbonates:
The real 

## 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**

**Notes:**
Martin, S, MD Castets, and J. Clavier (2006) Primary production, respiration and calcification of the temperate free-living coralline alga Lithothamnion corallioides, Aquatic Botany 85(2): 121-128

## Recent ‘discoveries’:   Rhodoliths / Maerl Beds

***Foster 2001***

**In high latitudes, usually clear water**
**  **
**In tropics/ subtropics, where coral reefs are unsuccessful**

***McCalester***

## Bosence & Wilson 2003 (NE Atlantic Maerl Beds)

*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. *

|  | Production
g CaCO3 m–2 y–1 | Accumulation
(m ky–1) |
| --- | --- | --- |
| 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 |

**Notes:**
While widespread, these other carbonates do not tend to produce thick deposits.
But preservation is the issue – most of these are not build-ups, hence not long-term CaCO3 sinks
Major buildups are in tropics – corals (aragonite) and algae (HMC)
Max buildups of cold-water coral banks: ???
- What IS the volume of sed being produced?  Some deposits are quite thick but are accumulations over several glacial cycles (see Roberts review paper)

## Recent ‘discoveries’:   Cold-water corals(not quite “shelf” deposition) 

**Roberts et al. *****Science***** 2006**

**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)**

**Notes:**
The discovery of how widespread cold water coral bioherms is remarkable.  These have certainly turned some heads.  Some of these deposits are quite thick, and like coral reefs, have accumulated over multiple glacial cycles (apparently the bioherms cease growing during sea level lowstands (in high latitudes, this is because of too cold waters, particularly for Lophelia – tropical mounds may be more continuous).  
“corals occur 
individually,
isolated colonies,
small patch reefs several meters across
large reefs and giant carbonate mounds up to 30 m high and several kilometers in diameter (over thousands to millions of years)
Their accumulation rates appear to be much slower than those of reefs, and the larger mounds appear to be a combination of carbonate and hemipelagic seds that are baffled in the framework
While these have an impact on the carbon cycle, it is unclear whether their production would have changed enough between glacial/interglacial cycles to contribute to the mechanism in the “coral reef hypothesis”
However, it will be interesting to see how these size up compared to tropical coral reefs.

## Coral Reefsand the Carbon Cycle

**Coral Reefs****and the Carbon Cycle**

***AIMS***

**Background on Reefs and Carbon**
**More than Reefs?**
**Reef CaCO****3**** Production & Accumulation**
**Controls on Reef Calcification**

**Notes:**
Two Main points

How well can we quantify shelf calcification?
What controls shallow benthic calcification?

Justification:  shallow benthic calcification affects the carbon cycle

## Budget for Reef: 		Greef + Dreef + Tr 	(net Gshelf > Greef)

**Budget for Reef:**** ****	****	****G****reef**** ****+ ****D****reef**** ****+**** ****Tr**** ****	****(****net G****shelf**** > G****reef****)**
**Budget for C-Cycle:  ****	****G****shelf**** ****+ ****D****shelf**

**G = Community calcification + inorganic cementation **
**(+)**

**D = Dissolution **
**(–)**

**Tr = Transport on/off reef **
**(+ or –; usually –)**

**Rates vary with T, ****Ω****, light, ...**

**Export limits reef development without necessarily affecting carbon cycle.**

**Rates vary with T, ****Ω****, bioerosion ...**

**Rates vary with framework versus sediments, hydrodynamic regime, shelf morphology, ...**

## 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 |
| ΔAlk of monoculture or ΔpH-ΔO2 | 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 |
| ΔAlk of closed system | Gsys + Dsys+ Gsys
 | Discrete measurements over duration of experiment |
| ΔAlk 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 > millenia |

**Calcification Measurements****(not always the same thing)**

**Organisms & Communities**

**Systems**

**Notes:**
For example, anything measuring calcification over timescales of less than a full diurnal cycle is likely to miss any significant dissolution 
In measurements of organism calcification, the alkalinity anomaly technique has been widely used, but it has probably not been properly calibrated against other methods over similar timescales, such as buoyant weight or coral band increments.

The alkalinity anomaly technique has also been used in the field, and usually one has to make estimates about the amount of mixing that is occurring.

The most time-integrated measurements, of course, are sedimentological.  The best way to do this is to estimate the total volume of material that has been deposited on an entire reef, over a discrete period.  
Almost always, these estimates come from coral cores, which is probably the best we can do, but it can lead to spurious results:

As biologists, we like to start with the calcification rates of an individual organisms, estimate the density of the organism and from there, gets some kind of estimate averaged over a square meter or so.

## Alkalinity

**Dissolution**

**Photo/Resp.**

**Inorganic**
**Cementation**

***Net organism ***
***calcification***

**Dissolution**

**Organic **
**Matter**
**Resp.**

**Inorganic**
**Cementation**

**Bioerosion**

**Dissolution**

***Net reef ***
***accumulation***

****

**Calcification**

***Inputs from land***

***export***

***Exchange with the ocean***

**Net**
**organism**
**calcification**

**Alkalinity**
**Anomaly**

**Sediment**
**Volume**

**Notes:**
Measurements vary widely depending on what’s being measured.  Some measurements capture only a few processes, others are the “end result” such as the accumulation of the reef itself.

## 0.8-1.5 g cm2 y-1

**Dissolution**

**Photo/Resp.**

**Inorganic**
**Cementation**

***Net organism ***
***calcification***

***Bioerosion***

***Dissolution***

**Calcification**

***export***

**0.8-1.5 g cm****2**** y****-1**

**0.1-1.3 g cm****2**** y****-1**

**0.75-0.90 g cm****2**** y****-1**

**0.004-0.07 g cm****2**** y****-1**

**0.1-0.5 g cm****2**** y****-1**

***Net community***
***calcification***

***Net reef***
***accumulation***

**Notes:**
Measurements vary widely depending on what’s being measured.  Some measurements capture only a few processes, others are the “end result” such as the accumulation of the reef itself.

## A High Preservation Rate?

**Reef accumulation rates indicate **
**very little carbonate loss**
**    ****... OR ...**
**today’s 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.**

**Notes:**
Measurement			g cm-2 y-1
Measured coral calcification rate	0.5-2.8 g	(1.2)   
  (surf area of organism)*
Alkalinity anomaly est.		0.05-1.26
Integrated net reef accum from cores	0.1-1.8 	(0.75)
Present-day bioerosion rates	0.1-0.5

## Changes in Reef CaCO3 Accumulation Over Time(Wistari Reef, Australia)

**       ****2         4         6          8       10**

**    ****10     9      8      7      6       5      4       3      2     1     0**

**Accum. Rate g cm****-2**** y****-1**

**10****3**** Years Before Present**

***Ryan et al. 2001***

**Average Holocene Accumulation**

**Accumulation History**

**Notes:**
Figure 4 from Ryan, Opdyke and Jell, 2001. Holocene Sediments of Wistari Reef:  Towards a global quantification of coral reef related neritic sedimentation in the Holocene.

“Calculated cange in accumulation rates needed to obtain the mass of carbonate observed at Wistari Reef.  The platform is assumed to have flooded between 8500 and 9000 years bp.

## Post-glacial Reef Deposition

**9000 ybp**

**8000 ybp**

**7000 ybp**

**5000 ybp**

**5000 ybp**

**3000 ybp**

**T****R****↑**

**Reef growth progressively limits**
**hydrographic exchange and**
**residence time increases **

## Saturation State Changes with Residence TimeBroecker & Takahashi 1966

**Saturation State Changes with Residence Time*****Broecker & Takahashi 1966***

**Bahamas Bank**

**Notes:**
The more highly supersaturated the waters, the more CaCO3 precipitates.  Precipitation of calcium carbonate over the banks is a second-order kinetic reaction, depending on the degree of supersaturation of the bank water.

## Calcification Rates

**G = ****ƒ****(z,Tr)**
**Carbonate production is favored at edges of the platform and slows down dramatically beyond 20 m of edge.**

***Demicco & Hardie, J. Sed Res. 2002***

**G (kg m****-2**** y****-1****)**

**Tr (days)**

**0.0**

**5.5**

**200**

**0**

**Calcification Rates**
**versus**
**Residence Time**
***Demicco & Hardie 2002***

**Notes:**
Demicco and Hardie 2002:
Modeled effect of residence time on calcification rate:
FIG. 5.—Model of carbonate production on the Great Bahama Bank with exponential fit of Figure 4. 
A–C) Values are in kg/m2/y. 
Production as a function of residence time and water depth for maximum production model
Minimum production model
Broecker and Takahashi’s approach but with correct depths
D)  Residence time on the Great Bahama Bank interpolated as described in the text.

## Growth forms can affect production and accumulation rates per m2

- Did the emergence of *Acropora* accelerate carbonate production?

- 18,300 g m-2 y-1

- 7,000 g m-2 y-1

**NOAA**

## Model of Reef Growth versus Sea Level Rise

**Model of Reef Growth versus ****Sea Level Rise**

- drowned/
- sediment

- massive

- branching 1

- branching 2

- seafloor

**120 m**

**Notes:**
CaCO3 accumulation has been extremely important in the ability of coral reefs to keep up with sea level rise.  
This movie starts during the Last Glacial Maximum (18,000 years ago), and shows reef growth in response to sea level rise during that time.  
The four posts provide the perspective of depth, and each represents 120 m.  
As the movie progresses, reefs begin to grow upward – some reefs accumulate calcium carbonate fast enough to keep up with sea level, and some don’t (those that don’t will turn white).  
There are two coral types that do well in this simulation: the massive corals, colored green, and the fast-growing branching corals, shown in light blue. 
 Watch what happens as sea level rises... (run movie). 
What we see are that the branching corals are the big contributors to the reef growth and that they dominate the building of the reef.  If this type of coral had been killed off, or if their growth rates would have been 30% less, then many more of these reefs would have “drowned” during sea level rise. Our barrier reef systems that we have today would look very different.  

## Coral Reefsand the Carbon Cycle

**Coral Reefs****and the Carbon Cycle**

***NOAA***

**Background on Reefs and Carbon**
**More than Reefs?**
**Reef CaCO****3**** Production & Accumulation**
**Controls on Reef Calcification**

**Notes:**
Two Main points

How well can we quantify shelf calcification?
What controls shallow benthic calcification?

Justification:  shallow benthic calcification affects the carbon cycle

## Physical Variables that Affect Calcification

- Temperature		**Latitude**
- Saturation State		**Latitude**
- Irradiance			**Depth, Latitude**

**Ω**

**T**

**Notes:**
We know a little more about the effects of increased CO2 on calcification.

Three main PHYSICAL variables affect calcification in photosynthetic organisms:
Temperature – affects both the biology of the organism and the chemistry of the water
Chemistry – the availability of calcium and carbonate ions for calcification
Light – affects photosynthesis: carbon uptake rate

But of course, not all organisms are created alike, and their biological differences make a difference in determining just how a decrease in saturation state will affect a particular organism.
These variables include such things as evolutionary history, their mineralogy, and just how they lay down their shells

## “Darwin Point”

**Between Equator and 30****o**** 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**

## The basic calculation:

**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.**

## G = Gmax tanh Iz/Ik

**G = G****max**** tanh I****z****/I****k**

**Z****max**** = log(I****min****/I****surf****)**
**                      ****K****490**

**I****z**** typically 2000 ****μ****Eins m****-2**** s****-1**
**I****k**** 250-300 ****μ****Eins m****-2**** s****-1**
**... ****light is not limiting at surface**

## LightOnly

**Light****Only**

***clear***

***murky***