cc: jcole@geo.Arizona.EDU, sandy.tudhope@ed.ac.uk, k.briffa@uea.ac.uk, mhughes@ltrr.arizona.edu
date: Fri, 11 May 2001 14:43:54 +0100
from: "Sandy Tudhope" <sandy.tudhope@ed.ac.uk>
subject: Re: comments?
to: Keith Alverson <keith.alverson@pages.unibe.ch>

Hi Keith et al.,

I've taken a quick look at the coral section, and have made some 
changes. I attach (and append below) a reworded version of the 
second coral paragraph (the one which starts "Unfortunately, many 
corals have been destroyed ....." in the first version).

Specific comments include:

1.  Worth pointing out that large corals (>100-200 years old) are 
relatively rare in most areas, and once the corals die, their 
skeletons are ofen rapidly removed by erosion, and the absolute 
chronology is lost.  i.e., we can't simply find go and core 'dead' 
corals and expect to get the same results.

2.  The issue about coral bleaching affecting the ability of corals to 
reproduce is a bit of a red herring in this context.  We are more 
concerned with the potential death of the large living corals, rather 
than the fact that we may have fewer new coral recruits.

3.  I've added a specific reference relating to the potential impact of 
global warming on corals and coral reefs.  

Hope this helps.

Cheers,

Sandy

______________
"Large living corals (>100-200 years old) suitable for climate 
reconstruction purposes are relatively rare in most reef areas of 
the world.  Unfortunately, a significant number of these corals 
have been killed in recent years, and the outlook for many others 
may be bleak.  Local factors related to coastal development 
and population pressure (such as dredging for engineering 
works, dynamite fishing, siltation and pollution from coastal land-
use changes) are taking their toll.   However, perhaps more 
significant is the widespread mortality of corals due to coral 
bleaching consequent on exceptional warm climatic extremes. 
 These extremes are often associated with El Nio events, and 
have been observed in all the worlds tropical oceans (Strong 
1998).  Coral bleaching describes the loss of colour of reef 
building corals due to the expulsion of symbiotic algae (or loss of 
their photosynthetic pigments) from the coral tissue.  The most 
common cause of coral bleaching is elevated sea surface 
temperature.  Specifically, bleaching often occurs when local 
SSTs exceed their usual warm season maximum by >1-2 C for 
periods exceeding a few weeks.  In some cases, other 
environmental factors such as low salinity or increased exposure 
to solar radiation are also implicated.  Once bleached, the corals 
have lost a major source of their nutritional energy (which comes 
from their algal symbionts), have very limited ability to calcify, 
and, if the condition persists, the corals die.  Major bleaching 
events associated with the 1982/83 and 1997/98 El Nio events 
caused mass mortality of corals in large areas of the equatorial 
Pacific, and western Indian Ocean.  Even the corals that recover 
from bleaching may have reduced fecundity and reduced 
tolerance to future stress (Normile, 2000).  The death of corals 
being used to reconstruct paleoclimate is not a theoretical 
problem  it is real.  Once the corals die, the potential for 
climate reconstruction from the skeletons is severely reduced.  
The dead coral skeletons are prone to rapid physical and 
biological erosion, and the absolute chronology (a key factor in 
identifying leads and lags in the climate system) is lost.  As one 
example, the Urvina Bay coral site in the Galapagos, the subject 
of several published investigations, was wiped out by the 
1982/83 El Nio (T. Guilderson, personal communication).  
Some scientists predict a global demise of coral reefs within the 
next few decades due to global warming (e.g., Hoegh-Guldberg, 
1999; Dawson et al, NOAA).  An overview of areas thought to 
be susceptible to bleaching can be found at: 
psbsgil.nesdis.noaa.gov:8080/PSB/EPS/SST/clim&hot.html



Hoegh-Guldberg, O.  (1999). Climate change, coral bleaching 
and the future of the world's coral reefs. MARINE AND 
FRESHWATER RESEARCH, 50 (8): 839-866 1999). "


__________________________________
Dr Sandy Tudhope
Department of Geology & Geophysics,
Edinburgh University,
West Mains Road,
Edinburgh EH9 3JW,
Scotland, U.K.

Tel:  +44 131 650 8508 (direct)
      +44 131 650 4842 (Secretary)
Fax:  +44 131 668 3184
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