Wednesday, May 23, 2012

4614.txt

cc: jcole@geo.Arizona.EDU, sandy.tudhope@ed.ac.uk, k.briffa@uea.ac.uk, mhughesatXYZxyzr.arizona.edu
date: Fri, 11 May 2001 14:43:54 +0100
from: "Sandy Tudhope" <sandy.tudhopeatXYZxyzac.uk>
subject: Re: comments?
to: Keith Alverson <keith.alversonatXYZxyzes.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 Ni�o events, and
have been observed in all the world�s 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 Ni�o 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 Ni�o (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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