[Coral-List] Answer to RE:HadISST: Bleaching is not due to Warming

[Martin P ê cheux]

Dear Coral Listers,

Thanks to all people with interest in the long version of my draft, and of
the critics of my ideas. I still feel confident about them. Here is the
reply to the critics.

ON THE EMAIL

> yours [facts] are unreviewed and unsubstantiated. Why not use the age-old
>method and submit your manuscript to proper peer-review?
Of course I will. But it takes a very long time to be published (last time
three years for me) with often interdiction to put the article on the Web.
Colleagues exchange drafts, so why not on Internet ? Every one know if he is
able to judge. It can improve the quality of the manuscript. And make the
Coral-List more scientifically valuable. So does the physicians community,
as I was told.

THERE WERE HIGHER TEMPERATURE BEFORE 1979 THAN NOW WITH SOME BLEACHING

>The only problem is that one can use, very successfully, satellite
>measurements of SST anomalies and predict mass coral bleaching...  Also - how
>many major bleaching events have occurred without an associated SST anomaly?
>Not many, it seems.
YES, and I quote the method "quite successful". The problem is not if
bleaching is associated with SST anomalies, but if such anomalies are new,
what I contest. If there would have been satellite measurements in
1950-1978, they would have detect "bleaching ghost".

>The problem is basically that HadISST shipping lane temperatures are a very
>poor indicator of temperatures on coral reefs. I've looked at the HADSST data
>for the GBR and compared ... from my in-situ temperature loggers (on reef flats
>and slopes) and there are big differences.
>Another more general problem is that monthly means are not a sensitive
>indicator of bleaching stress in corals. Corals will stress and die when daily,
>weekly or fortnightly temperatures reach unusual extremes, but these
>temperatures may not be reflected in unusually high monthly means.
Sure, that is always a problem and I must discuss it more in details :
- this is not the case for fore reef well bathed by oceanic waters, where
time dynamic is slow and bleaching is also encountered (so hold good
counter-examples). I know it is not the case for slope of GBR inshore reefs.
What about offshore ones ? I am interested by your analysis.
- there is generally good correlation (not equality !) between in situ and
ship measurements (refs in draft, in Pecheux, 1997, and Lough, 1999 in GBR),
even if:
- local spatial or temporal extremes occurs. But is there a reason that it
is a new feature, that extreme are more extreme than in the mid XX century ?
I guess not. On the contrary there is a slight increase in moisture deficit,
and more winds in tropics so less dolldrums, if there is any change.
- and, see above, NOAA measurement are quite successful in predicting
bleaching !!, with only double greater spatial resolution and time ones (but
generally integrated over weeks) than HadISST.
I estimate crudely the effect of local + other triggering factors to be of
the order of 0.4°C ("true" bleaching threshold minus calculated minimum
bleaching threshold) (to be added in the article).

BLEACHING BEFORE 1979

>Why we seem to have a huge discrepancy in bleaching events pre-1978 and
>post-1978 could probably be attributed to the sudden increase in reporting,
>observer abundance. Couldn't it be so that bleaching events occured at rather
>high frequencies pre-1978 but that we had a lack of substantial effort in
>actually reporting these?
NO. See draft for references. And from another reply :
>For everyone who used to dive along his life since more than two or three
>decades ago, it is clear that bleaching was not common before 1978. I have
>been diving since I was 8 years old in Cuban reefs (now I am 56), and never
>observed a coral bleaching event before the 80s. I do not believe it is a
>matter of more frequent reporting.

OTHER CAUSES ?

>The primary factor affecting coral UV exposure,..., is not low latitude ozone
>variation, its changes in the quantity ... of chromophoric dissolved organic
>matter.  For this reason, simply considering that ozone content is fairly
>stable in the tropics is not reason enough to disregard the potential
>importance of variation in UV.
The main argument against that is that bleaching occurs also just below the
surface, so the effect of DOM can be only very small. And what can be
invoked to justify a global change of transparency of such water ? If it
were the case, speak of "water transparency" and not "UV" as the cause of
mass bleaching... And I am sure that clearest as possible waters exist
before 1978 in summer.

>One possible explanation is that today, with so many chronic stresses
>afflicting reefs simultaneously, corals are more susceptible to heat stress and
>are capable of bleaching at lower temperatures than decades ago.
Yes and no. Yes, coral are more susceptible to heat stress, but no, "so many
chronic stresses". If one checks all the stress possibilities responsible of
bleaching, it is not local human impact, not sea level rise, not
nutrients...not UV, not hydrological change. So now come only :

CO2

>To conclude that the cause is CO2, you need to provide data that CO2 in coral
>reef waters is increasing in a way that you feel temperature is not.
I don't understand. CO2 have increasing by 1980 by 30% everywhere, and it
dissolves in every shallow waters, with lowering of pH, it is pure physic
and chemistry. And all pH value are shifted down by about -0.085 pH unit for
mean reef seawater (+21% proton). I do not have to provide more data.
I just found a strange remark. In December 1981, alkalinity was "almost
certainly too low" at Davies reef, GBR (Barnes, 1988) where bleaching was
"not nearly as conspicuous" as elsewhere (Oliver, 1985) (see in Pecheux,
1997)
Temperature is rising but not in Caribbean till 1986. And again, within the
warming trends, there was higher SST 1950-1978 without bleaching than now
with it.


>These results seem a little questionable given that in several lab
>studies... a doubling of atmospheric CO2 was mimicked ...(max 2 months)... and
>no bleaching was reported.
This is a question already discussed in October 2003 on the List, and is not
the purpose of the article. The problem is the SYNERGY with temperature,
light and water agitation. I do not have enough data, and only from
fluorescence measurements in one hour incubations, with INCREASE of Fv/Fm
with T and CO2, decrease with light (Pecheux, 2002, Mar. Life, 12, 63-6;
Coral list 6/10/2003; www.reefbase.org).

When the temperature and light are normal in those lab studies, reef
symbioses can withstand doubling, quadrupling (Biosphere 2) CO2 level. Very
important, in Stylophora pistillata from ?Djibouti for 5 weeks, at 380µE
light, photosynthesis and calcification decrease (by -34% and -50%) with CO2
rise (from 460 to 766ppm) at high temperature (28.2°C) but not at normal one
(25.2°C) (by -17% and +5%) (Reynaud et al., 2003, Global Change Biol., 9,
1-9). If I understand well, at still higher but not exeptional temperature,
collapse and bleaching is expected with CO2 rise.
Under summer temperature (22.5 to 24°C), light (75 to 55àµE/m2.s) and low
water agitation stresses, I saw in S. pistillata from Aquaba fast visible
paling in 2 days at 1000ppm CO2, bleaching at 5000ppm in 1 day, nothing in
normal CO2. I have posted in ReefBase the abstract of this first experiment
(1994, Europ. Meeting Coral Reef, Luxembourg; Pecheux, 1997, appendix I).

I would be very pleased if others do similar tests, as I have no more
laboratory. 


>Could not the SST anomalies indicate higher ability to dissolve CO2 and
>therefore indicate potential bleaching due to this theory?
Reply from another:
>CO2 becomes more soluble in seawater as the water becomes colder,
>not warmer.  As SSTs increase the saturation state of aragonite... will
>likewise increase, although the temperature affects will likely be negligible
>in comparison to the chemical.
Yes. The main effect of warming would be that, in a mass of water and
isolation given slow exchange with air, the CO2 pressure rises (+14ppm/°C),
inducing a lowering of pH, but of about only -0.01 unit/°C, and little
lowering of CaCO3 saturation. Negligible in a first approach.

For most of those topics above see Pecheux (without ê), 1997, at
www.reefbase.org.

I hope that this email was enlightening.
Cheers,


Martin Pêcheux, Scientific Consultant/IPCC
3, allée des Elfes, 94260 Fresnes, FRANCE
+33 1 42 37 41 96
martin-pecheux at wanadoo.fr