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Warming and Acidifying Ocean and Coral growth

Jung Ok Kang and Malcolm T. McCulloch

Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia

Figure 1. Geographic locations of coral collection sites.


Coral reefs generally are developed within relatively narrow area when environmental controls on the growth of corals including seawater temperature, light, and aragonite saturation states, water motion, and water quality are satisfied. Increasing atmospheric carbon dioxide concentration has been affected on coral reefs mainly through two kinds of mechanisms. Firstly, global warming or climate change has caused rising seawater temperature and extraordinally warm temperature cause corals to bleach. This process has already had a serious impact on the world's coral reefs, with almost 30% of corals having disappeared since the beginning of the 1980s by bleaching events (Hoegh-Guldberg, 2005). Besides, the rise in the concentration of carbon dioxide in the atmosphere has an influence on coral reefs since a decrease of ocean acidity by increasing atmospheric carbon dioxide lower the aragonite saturation states of seawater, declining available carbonate ions of seawater to calcification.

Several experimental and modelling studies were performed under conditions expected in the 21st century and the results show that acidifying ocean will compromise coral calcification. Thermodynamic calculation shows that a doubling of carbon dioxide in seawater will be a decline in carbonate ion concentration of 25-35% to the preindustrial concentration (Landon et al., 2000). Moreover, the worst cast of modelling study argues that total preindustrial to 2100 calcification decrease could be as high as 17% to 35% depending on the regions (Kleypas et al., 1999). The shapes of the calcification versus aragonite saturation curve which are from laboratory studies and crucial in predicting future changes in coral reef, however, still have many uncertainties because the data is scare and is constrained with a first approximation of the general response of coral reefs. In addition, time of exposure to manipulating conditions is too short to apply to the real world and the synergistic interaction of elevated temperature and lowering aragonite saturation state is unknown. Therefore, my project aims to understand how anthropogenic climate change and increasing ocean acidity affect coral reefs in real and various paleo-evironmental proxies will be used to provide the evidences of the changes in coral-reef pH representing ocean acidity and sea surface temperature indicating global warming and the responses on coral calcification rate. For the first place, the massive corals of genus Porites were collected from Southern Great Barrier Reef in October of this yesr (Figure 1). Since they are long lived, distributed widely throughout the Indo-Pacific Ocean, from inshore to offshore waters, their skeletal records are useful as a tool for detecting long-term changes in environmental conditions in ocean surface waters. At the same time, the determination of calcification rate for Porites corals collected in 2006 from Pompey complex is in progress.     

 


Hoegh-Guldberg O (2005) Low coral cover in a high-CO2 world. Journal of Geophysical Research 110: C09S06
Kleypas JA, Buddemeier RW, Archer D, Gattuso J-P, Opdyke BN (1999) Geochemical consequence of increased atmospheric carbon dioxide on coral reefs. Science 284: 118-120
Langdon C, Takahasi T, Sweene C, Chipma D, Goddard J, Marubini F, Arceve H, Barnett H, Atkinson MJ (2000) Effect of calcium carbonate saturation state on calcification rate of an experimental coral reef. Global Biogeochemical Cycles 14: 639-654