[Coral-List] Ocean acidification and calcification

Thomas Goreau goreau at bestweb.net
Sat Feb 14 08:50:33 EST 2009

I thoroughly agree with all the thoughtful comments made below by  
Gledhill, Feely, Manzello, Yates, Wanninkof and Langdon below  
regarding ocean acidification as a serious, long-term global threat.  
There is no doubt that coral calcification will be impaired long  
before actual dissolution takes place. But corals have the  
physiological mechanisms to maintain a very different internal  
chemistry than that of the ocean, and keep calcifying even when the  
skeleton dissolves. My point is only that the far bigger and  
IMMMEDIATE threat to reefs now is that corals are bleaching and dying  
on a huge scale due to high temperatures, stopping all their  
calcification immediately, while the few survivors will only be  
slightly impaired in the future. Both temperature and acidification  
are directly linked to CO2 increases, but their urgency with regards  
to reefs depends on their time constants, one is short, one is much  
longer. Once again, if we take care of CO2 in time to stop bleaching,  
acidification will automatically be taken care of, but not the  
converse. That is why we should all agree that urgent decreases in  
atmospheric CO2 concentration are essential to save reefs on the time  
scale of the most immediate threats against them.

> Date: Fri, 13 Feb 2009 15:35:55 -0500
> From: Dwight Gledhill <Dwight.Gledhill at noaa.gov>
> Subject: [Coral-List] Coral bleaching and ocean acidification
> To: coral-list at coral.aoml.noaa.gov
> Message-ID: <4995D9AB.1010009 at noaa.gov>
> Content-Type: text/plain; charset=windows-1252; format=flowed
> Both climate-scale threats of thermal stress and ocean acidification
> pose a daunting challenge to tropical coral reefs. Attempting to  
> decide
> on the gravest threat between the two may represent a futile effort.
> Both processes are intrinsically linked perhaps not only by means of
> their dependence on atmospheric CO_2 concentration, but more recent
> evidence suggest that thermal stress and high-CO_2 may act
> synergistically to lower bleaching thresholds [Anthony et al., 2008].
> Consequently, we enthusiastically endorse Dr Goreau?s sentiment that
> CO_2 stabilization should be proactively sought after should we desire
> not to experience the first coral reef hiatus in modern human history
> (see Ridgwell & Zeebe, 2005 for some context). Considering the
> sustenance, coastal protection, and geochemical services currently
> afforded to human civilization by these ecosystems, this would be a  
> most
> unwelcome occurrence.
> That said, there are some common misconceptions about the concerns of
> ocean acidification to coral reefs and inaccuracies regarding the sea
> surface carbonate chemistry as presented by Dr Goreau that we seek to
> clarify in this response. A common misconception is that the primary
> threat ocean acidification poses to coral reef ecosystems is
> dissolution. As Dr Goreau correctly points out, it will be several
> centuries before our current CO_2 trajectories would induce  
> dissolution
> in most oceanic tropical surface waters (not accounting for upwelling
> regions that are already impacted by high-CO_2 levels e.g., Manzello  
> et
> al., 2008). It is for this reason that while effects of rising CO_2 on
> ocean chemistry have been discussed for at least three decades [e.g.,
> Broecker /et al./,1971; Bacastow and Keeling, 1972] it has only  
> recently
> been identified as a critical concern. The recent concern is rooted in
> experimental observations beginning in the 1990?s that reveal that the
> degree of carbonate mineral supersaturation (saturation state)  
> imparts a
> direct control on calcification rate [e.g., Gattuso et al., 1998;
> Marubini et al., 2001, 2002; Reynaud et al., 2003; Marshall and Clode,
> 2002; Ohde and Hossain, 2004; Borowitzka, 1981; Gao et al., 1993;
> Langdon et al., 2000, 2003; Langdon and Atkinson, 2005; Leclercq et
> al.,2000, 2002; Anthony et al., 2008]. Additional experiments have  
> since
> identified responses beyond calcification effects that could
> significantly impact community structure in other ways [e.g. Kuffner  
> et
> al., 2008]. Therefore, while most oceanic tropical surface waters will
> remain supersaturated with respect to aragonite for many years so as  
> to
> preclude actual dissolution, most experimental evidence suggest that  
> the
> rate of reef accretion will decline proportionally to declining
> aragonite saturation state perhaps compromising reef resiliency in the
> face of other acute threats (e.g bleaching, diseases, potentially
> increasing storm intensity, rising sea level). Any decline in
> calcification and, thus reef-building, is of grave concern for the
> persistence of reef systems because rates of accretion on healthy,
> undisturbed reefs are known to only slightly outpace rates of reef  
> loss
> (i.e., physical and biological erosion: see Glynn, 1997 for review)
> There are further complications to even this nuanced consideration
> however. Most reefs are not solely composed of aragonite but are  
> instead
> much comprised of more soluble high-Mg calcites [Morse et al., 2006].
> Furthermore, the diurnal amplitude in pCO_2 levels within the reef  
> zone
> can be 10 times that of the oceanic waters and often exhibit a step- 
> down
> in overall saturation state due to calcification and respiration
> processes. As a result, there may be periods at night when many reefs
> currently exhibit net dissolution [Yates and Halley, 2006]. Yates and
> Halley (2006) found that significant amounts of sediment (not coral)
> dissolution are already occurring (up to 71% of day time calcification
> rates), and suggest that by the year 2100, atmospheric pCO2 will  
> exceed
> the average pCO2 dissolution threshold of 585 microatm. This suggests
> that net sediment dissolution could exceed net calcification by 2100.
> So, while coral skeletons will likely not dissolve within the next
> couple of centuries, the sediments are already dissolving and this
> dissolution rate will likely exceed the calcification rate most of the
> time in the next century exacerbating the decline in rate of reef
> accretion. So while the primary threat from ocean acidification is
> commonly accepted to be the decrease in the rate of coral  
> calcification,
> the significance of the dissolution problem may be greatly understated
> despite the fact that oceanic tropical sea surface waters will remain
> supersaturated.
> With regards to Dr Goreau?s assessment of tropical surface water not
> being in equilibrium with atmospheric CO_2 we would encourage him to
> consult the recent literature reporting the results from the Bermuda
> Atlantic Time Series Study (BATS) [ Bates, 2007] where it is reported
> that ?surface seawater dissolved inorganic carbon (DIC) and pCO?_2
> increased annually at rates similar to that expected from oceanic
> equilibration with increasing CO_2 in the atmosphere.? Furthermore,  
> this
> is consistent with the global synthesis of Takahashi et al., (in  
> press)
> as well as the recent findings for the Greater Caribbean Region  
> based on
> underway pCO_2 data collected aboard the Explorer of the Sea?s since
> 2002 [Gledhill et al, 2008, http://coralreefwatch.noaa.gov/satellite/oa 
> ]
> where we find aragonite saturation states declining at about 3% per
> decade. We find similar correspondences between atmospheric CO_2 and  
> sea
> surface carbonate chemistry at the Hawaiian Ocean Time-series over the
> past 20 years [Doney et al., 2009]. One should also consult the
> pioneering work of Sabine et al (2004) which specifically quantifies  
> the
> uptake of anthropogenic CO_2 in the global surface oceans and
> demonstrates that even in the surface waters of the equatorial Pacific
> there has been an uptake of more than 40 micromoles/kg of  
> anthropogenic
> CO_2 . The impacts of which are detailed by Feely et al (2004) which
> describe these changes as being perhaps the most significant in  
> surface
> carbonate chemistry in more than 20 million years.
> Finally, it may be worth considering that ocean acidification  
> represents
> a chronic, long-term threat, whereas, to-date, thermal stress has been
> short-term, albeit highly acute. Connell?s (1997) pioneering long-term
> studies of coral reef response to both acute and chronic disturbances
> have shown that reef systems are more vulnerable to chronic  
> disturbance
> and can recover from short-term, acute disturbances. Implicit in this
> statement is that the frequency of recurrence for the short-term,  
> acute
> disturbances is not too rapid. If so, then acute disturbances then
> behave more like a chronic disturbance and allow little if any  
> recovery
> of the reef community. Time will tell what the actual frequency of
> bleaching events will be and how corals respond, but one thing that
> isn't questionable is that the effects of ocean acidification will be
> cumulative, chronic and long-term; affording no recovery periods or
> respite from the globally-imposed declines in calcification.
> Anthony, K. R. N., D. I. Kline, et al. (2008). "Ocean acidification
> causes bleaching and productivity loss in coral reef builders."
> _Proceedings of the National Academy of Sciences of the United  
> States of
> America_ *105*(45): 17442-17446.
> Ridgwell, A. and R. E. Zeebe (2005). "The role of the global carbonate
> cycle in the regulation and evolution of the Earth system." _Earth and
> Planetary Science Letters_ *234*(3-4): 299-315.
> Manzello, D. P., J. A. Kleypas, et al. (2008). "Poorly cemented coral
> reefs of the eastern tropical Pacific: Possible insights into reef
> development in a high-CO2 world." _Proceedings of the National Academy
> of Sciences of the United States of America_ *105*(30): 10450-10455.
> Broecker, W. S., Y.-H. Li, and T.-H. Peng (1971), Carbon dioxide:  
> Man?s
> unseen artifact, in Impingement of Man on the Oceans, edited by D. W.
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> Bacastow, R., and C. D. Keeling (1972), Atmospheric carbon dioxide and
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> Technical Information Center, U.S. Atomic Energy Commission,  
> Washington,
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> Buddemeier (1998), Effect of calcium carbonate saturation of  
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> coral calcification, Global Planet. Change, 18, 37?46. Marubini, F.,  
> H.
> Barnett, C. Langdon, and M. J. Atkinson (2001), Dependence of
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> hermatypic coral Porites compressa, Mar. Ecol. Prog. Ser., 220, 153? 
> 162.
> Marubini, F., C. Ferrier-Pages, and J.-P. Cuif (2002), Suppression of
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> 270, 179?184.
> Reynaud, S., N. Leclercq, S. Romaine-Lioud, C. Ferrier-Pages, J.
> Jaubert, and J.-P. Gattuso (2003), Interacting effects of CO2 partial
> pressure and temperature on photosynthesis and calcification in a
> scleractinian coral, Global Change Biol., 9, 1660? 1668.
> Marshall, A. T., and P. Clode (2002), Effect of increased calcium
> concentration in sea water on calcification and photosynthesis in the
> scleractinian coral Galaxea fascicularis, J. Exp. Biol., 205, 2107?  
> 2113.
> Ohde, S., and M. M. Hossain (2004), Effect of CaCO3 (aragonite)
> saturation state of seawater on calcification of Porites coral,  
> Geochem.
> J., 38, 613?621.
> Borowitzka, M. A. (1981), Photosynthesis and calcification in the
> articulated coralline alga Amphiroa anceps and A. foliaceae, Mar.  
> Biol.,
> 62, 17? 23.
> Gao, K., Y. Aruga, K. Asada, T. Ishihara, T. Akano, and M. Kiyohara
> (1993), Calcification in the articulated coralline alga Corallina
> pilulifera, with special reference to the effect of elevated CO2
> concentration, Mar. Biol., 117, 129?132.
> Langdon, C., T. Takahashi, C. Sweeney, D. Chipman, and J. Goddard
> (2000), Effect of calcium carbonate saturation state on the
> calcification rate of an experimental coral reef, Global Biogeochem.
> Cycles, 14, 639?654.
> Langdon, C., W. S. Broecker, D. E. Hammond, E. Glenn, K.  
> Fitzsimmons, S.
> G. Nelson, T.-H. Peng, I. Hajdas, and G. Bonani (2003), Effect of
> elevated CO2 on the community metabolism of an experimental coral  
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> Global Biogeochem. Cycles, 17(1), 1011, doi:10.1029/ 2002GB001941.
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> photosynthesis and calcification of corals and interactions with
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> Geophys. Res., 110, C09S07, doi:10.1029/2004JC002576.
> Leclercq, N., J.-P. Gattuso, and J. Jaubert (2000), CO2 partial  
> pressure
> controls the calcification rate of a coral community, Global Change
> Biol., 6, 329?334.
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> production,
> respiration, and calcification of a coral reef mesocosm under  
> increased
> CO2 partial pressure, Limnol. Oceanogr., 47, 558?564.
> Kuffner, I. B., et al. (2008), Decreased abundance of crustose  
> coralline
> algae due to ocean acidification, Nature Geosci., 1(2), 114? 117.
> Morse, J. W., et al. (2006), Initial responses of carbonate-rich shelf
> sediments to rising atmospheric pCO(2) and ??ocean acidification??:  
> Role
> of high Mg-calcites, Geochim. Cosmochim. Acta, 70(23), 5814?5830.
> Yates, K. K., and R. B. Halley (2006), CO3 2 _ concentration and pCO2
> thresholds for calcification and dissolution on the Molokai reef flat,
> Hawaii, Biogeosciences, 3, 1? 13.
> Bates, N. R. (2007), Interannual variability of the oceanic CO2 sink  
> in
> the subtropical gyre of the North Atlantic Ocean over the last 2
> decades, J. Geophys. Res., 112, C09013, doi:10.1029/2006JC003759.
> Gledhill, D. K., R. Wanninkhof, et al. (2008). "Ocean acidification of
> the Greater Caribbean Region 1996-2006." _Journal of Geophysical
> Research-Oceans_ *113*(C10): -.
> Feely, R. A., C. L. Sabine, et al. (2004). "Impact of Anthropogenic  
> CO2
> on the CaCO3 System in the Oceans." _Science_ *305*(5682): 362-366.
> Sabine, C. L., R. A. Feely, et al. (2004). "The Oceanic Sink for
> Anthropogenic CO2." _Science_ *305*(5682): 367-371.
> Connell JH (1997) Disturbances and recovery of coral assemblages.
> /Proc.^ Eighth Int. Coral Reef Symp/ *1*:9- 21
> Doney, S.C., V.J. Fabry, R.A. Feely, and J.A. Kleypas (2009):
> <http://www.pmel.noaa.gov/publications/search_abstract.php?fmContributionNum=3230 
> >Ocean
> acidification: The other CO2 problem./ Annu. Rev. Mar. Sci./, /1/,  
> doi:
> 10.1146/annurev.marine.010908.163834, 169?192.
> Glynn PW (1997) Bioerosion and coral reef growth: a dynamic balance,  
> in
> /Life and Death on Coral Reefs/, ed Birkeland C (Chapman and Hall, New
> York), pp 68-95
> Takahashi, T., S.C. Sutherland, R. Wanninkhof, C. Sweeney, R.A. Feely,
> D.W. Chipman, B. Hales, G. Friederich, F. Chavez, A. Watson, D.C.E.
> Bakker, U. Schuster, N. Metzl, H. Yoshikawa-Inoue, M. Ishii, T.
> Midorikawa, C. Sabine, M. Hopemma, J. Olafsson, T.S. Arnarson, B.
> Tilbrook, T. Johannessen, A. Olsen, R. Bellerby, H.J.W. de Baar, Y.
> Nojiri, C.S. Wong, and B. Delille (2007): Climatological mean and
> decadal change in surface ocean pCO_2 , and net sea-air CO_2 flux over
> the global oceans. /Deep-Sea Res. {in press] {This paper is posted on
> the Deep-Sea Research Website}
> /
> /Note: this was a joint response authored by the following:
> /
> /Dwight K. Gledhill, NOAA Coral Reef Watch, (dwight.gledhill at noaa.gov)
> Richard Feely, NOAA PMEL, (Richard.A.Feely at noaa.gov)
> Derek Manzello, NOAA AOML (Derek.Manzello at noaa.gov)
> Kim Yates, USGS ,(kyates at usgs.gov)
> Rik Wanninkhof, NOAA AOML ,(Rik.Wanninkhof at noaa.gov)
> /
> /
> ///
> -- 
> Dwight K. Gledhill, Ph.D.
> I.M. Systems Group at National Oceanic and Atmospheric  
> Administration (NOAA)
> National Environmental Satellite, Data and Information Service  
> Coral Reef Watch
> Physical Scientist/Oceanographer
> E/RA31 SSMC 1 rm 5306
> Silver Spring, MD 20910-3226
> Email: dwight.gledhill at noaa.gov
> Ph: (301) 713-2857 x137; Fax: 713-3136
> http://coralreefwatch.noaa.gov/
> Date: Fri, 13 Feb 2009 21:30:44 -0500 (EST)
> From: "Chris Langdon" <clangdon at rsmas.miami.edu>
> Subject: [Coral-List] Co2 in tropical oceans
> To: coral-list at coral.aoml.noaa.gov
> Cc: clangdon at rsmas.miami.edu
> Message-ID:
> 	<2182. at webmail.rsmas.miami.edu>
> Content-Type: text/plain;charset=iso-8859-1
> The data speak for themselves. Take a look at the figures in Feely  
> et al.
> 2005 in Science.  By direct chemical measurement the dissolved  
> inorganic
> carbon concentration of the surface ocean has increased by approx. 40
> umol/kg between 1800 and 1994.  This is true throughout the tropics in
> Atlantic, Indian and Pacific Oceans.  Take a look at Fig. 3 in that  
> paper.
> The red zone representing an increase in CO2 of 40 umol/kg due to the
> uptake of fossil fuel CO2 in the surface ocean extends from pole to  
> pole
> in each ocean basin. If that isn't convincing take a look at the long
> term, high precision measurements at HOTS (23N 158W), BATS (32N 64W)  
> and
> ESTOC (29N 15W) all show a steady increasing trend in dissolved  
> inorganic
> carbon (DIC) of 1.2 umol/kg/y (Dore et al, 2003), 1.3 umol/kg/year  
> (Bates
> et al, 2002) and 0.4 umol/kg/y (Gonzalez-Davila 2003), respectively,  
> over
> the period 1988 to  2003.  These increases are very close to what  
> would be
> expected for a surface ocean staying in equilibrium with the  
> increasing
> inventory of CO2 in the atmosphere.  There is no controversy.  The
> increases are well documented by thousand of measurements and the
> mechanism understood.
> It would be nice to have some of these long term measurements at a few
> coral reef sites. There is no reason to expect that the basic  
> increasing
> trend would be different but the daily, seasonal and interannual
> variability would be of interest.
> Chris Langdon
> Assoc. Professor
> Uni. of Miami
> 4600 Rickenbacker Cswy
> Miami,FL 33149
> Ph: 305-421-4614
> Fax: 305-421-4239
> ------------------------------
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> End of Coral-List Digest, Vol 6, Issue 14
> *****************************************

Thomas J. Goreau, PhD
President, Global Coral Reef Alliance
Coordinator, United Nations Commission on Sustainable Development  
Partnership in New Technologies for Small Island Developing States
37 Pleasant Street, Cambridge MA 02139
goreau at bestweb.net

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