BLEACHING : NOT UV
micho at ccrv.obs-vlfr.fr
Fri Mar 29 06:55:06 EST 1996
FROM PECHEUX : pecheux at eureka.meta.fr
The following article was refused by Marine Ecology Progress Series (see at
end). Please, is there native English-speaking scientist who can check the
english before an other submission ? Thanks a lot ! Tables and figures send
Also any critics, comments, new informations are wellcome and may be taken
in account. It can be also be quoted as unpublished with now archive
coral-list server reference.
ANALYSIS OF OZONE SATELLITE DATA : NO RELATION BETWEEN UV AND REEF MASS
Martin Pecheux, Scientific Consultant, 8, rue Dante, F-06000 NICE, FRANCE.
Email : pecheux at eureka.meta.fr
Abstract : One of the major threats on Earth ecosystems is the recent and
worldwide mass bleaching of reef symbioses, yet unexplained. Global warming
or weather pattern change are probably not the causal factors. Many
researchers have conducted bleaching experiments with UV, supposed to
trigger bleaching events.
Here I analyze Nimbus 7 TOMS ozone data above reef areas from 1979 to 1991.
There is no trend in ozone amount in tropics at month, season nor year time
scale, nor more frequent or more pronounced low ozone values. Examination
of twenty bleaching events did not reveal any correlation with ozone
The UV hypothesis must be discarded, and this lets CO2 rise as the last
serious explanation of reef mass bleaching.
Key-words : ozone, TOMS, Nimbus 7, ultra-violet, reef, bleaching, CO2.
recent mass bleaching affects all reef photosynthetic symbioses, not only
hard corals but also other cnidarians, large foraminifers, sponges and
Tridacna mollusks, in association with either dinoflagellates, diatoms or
cyanobacteria, some with no mortality. It corresponds to the ruture of the
symbiosis with loss of the colored symbionts and/or the photosynthetic
pigments, hence the name. This phenomenon is worldwide and observed in all
reef biotopes, without coherent spatial pattern. It began in 1979, and
seems to increase in magnitude and frequency, becoming chronic (see reviews
of Williams and Bunkley-Williams, 1990, Smith and Buddmeier, 1992, Glynn,
1993, Pecheux, soon on Internet).
The most worrysome is that the cause is not identified. As bleaching
generally occurs during hot time, calm sea and clear sky, global warming
has been often invoked. But global warming is evenly distributed on Earth
(Jones et al., 1986, Gray, 1990 and ref. herein), in particular not found
over Caribbean (Atwood et al., 1992, IPCC, 1992). Temperatures are often
reported to be "above normal" during bleaching but long term data are
insufficient to label them as abnormally high, apart for the exceptional El
Nino 1983 in East Pacific (Glynn, 1989) but not elsewhere (Croffroth et
al., 1989). Morever, good counter-examples exist, as for the well studied
Great Barrier Reef 1982 event with normal temperature (Coffroth et al.,
1989) or bleaching of large foraminifers at less than 27oC in Florida
1991-1993 (Hallock and Talge, 1993, Hallock et al., 1995).
Convincing evidences of a climatic shift in the late 70's are accumulating,
primarly with an increase of evaporation in marine tropical areas (Flohn
and Kappala, 1989, Kumar et al., 1994, Graham, 1995), but with a pattern
similar to El Nino, i.e. not worldwide. Mass bleaching have been suspected
to be a consequence of formation of dense hot hypersaline waters (Jaap,
1988, Odgen and Wicklund, 1988, Lang et al., 1989), favourized by
evaporation, but such formation is excluded when slack winds (Pecheux,
1996, Annex 2). On the other hand, probable increase of mean wind speeds by
enhanced convection (Flohn and Kappala, 1989, but see Graham, 1995) seems
to rule out more frequent doldrum times in warm tropical areas.
With the coincidence of the advents of mass bleaching and the Antartic
ozone hole around 1979, many researchers have considered ultra-violet (UV)
as the primary cause. Many biological experiments have been carried out
(Scelfo, 1986, Siebeck, 1988, Lesser and Schick, 1989, Lesser et al., 1990,
Schick et al., 1991, Hallock and Talge, 1993, Reaka-Kudla et al., 1993,
Gleason and Wellington, 1993) and measures done in situ (Gleason and
Wellington, 1993, Drollet et al., 1994), although it was already known that
mean stratospheric ozone had not yet decreased in tropics (Bowman and
Krueger, 1985, Frederick and Serafino, 1985, Herman et al., 1991, Stolarski
et al., 1991, see last synthesis in Stolarski et al., 1992, Herman and
It was necessary to verify if this holds also at seasonal time scale, or if
variation had not increased with concomitent more frequent low ozone
values. A third posibility might have been that mass bleaching events would
be triggered by "mini-ozone holes". Ozone drawdowns are known to occur at
time scale of few days in latitude as low as Texas (Michaels et al., 1994).
Moreover these drawdowns are associated with anticyclonic features,
suggesting their advent during doldrum time, although this correlation is
the weakest in tropics (Barsby and Diab, 1995). In order to examine those
possibilities, I analyzed available data on ozone level in tropics, as
measured by the Nimbus 7 satellite.
Whole column ozone quantities have been mesured by the Solar Backscatter
Ultraviolet/Total Ozone Map Spectrophotometer (SBUV/TOMS) aboard the NOAA
Nimbus 7 satellite since November 1978. Its principle is based on the ratio
of sun backscatter radiations at 312 nm and 331 nm lengthwave, one strongly
absorbed by ozone while the other not. Data are freely available from the
Goddard Space Flight Center (DAAC User Service, Global Change Data Center,
Code 902.2, Greenbelt, MD 20771) in specific format of ASCII files on three
CD-ROMs covering the period from November 1978 to January 1991. Daily 200
000 measures over the globe are averaged in a grid 1o latitude x 1.25o
longitude, corresponding to 111 x 139 km squared at equator. Ozone
quantities are expressed in Dobson units, corresponding to hundreth of
millimeter of an equivalent pure ozone layer at sea level pressure and
temperature. Missing values represent 2.4% to 5.7% of the data, evenly
distributed in first approximation (not shown).
I selected 36 reef locations, using ozone values of the nearest TOMS grid
point (Tab. 1). Spatial ozone gradient is weak, with absolute difference
between adjacent squares of a mean and standard deviation of about 3
Dobsons, and maximum difference roughly ten time greater, as checked in the
GBR and Florida areas. I restricted the data from the 1st January 1979 to
the 31th December 1991 (4745 days) to eliminate winter biais in trend
analysis. Programs of data extraction from CD-ROMs, with patch reads by
trap calls to Operating System primitives for reasonnable speed of lecture,
and those of data analysis were written in Think PascalR on Macintosh, and
displayed with StatViewR.
As it was already known, there is no decrease of ozone level in tropics
between 21.5oS to 20.5oN for studied locations, with p always > 0.05 for
1979 to 1991. Even positive trends are observed in Chiriqui and San Blas,
Panama, and Venezuela (with p=0.009, 0.017, 0.056 respectively). North of
20.5oN, decrease of ozone becomes sensible (p<0.0005), with trend downto
1.2% per year in Aqaba (with no mass bleaching) and Bermuda. A similar
pattern is seen with selection of the lowest values of each month, with
p<0.05 only north of 29.5oN (one value selected) or north of 26.5oN (four
values selected), exception Oahu, 21.5oN, with a weak trend=-0.475
Dobson/year, p=0.029, r2=0.764.
Trends for each month are similar, with no significant trend between at
least 15oS and 15oN. They group into the four seasons (Fig. 1). In the
Southern hemisphere, a weak negative trend is observed in summer,
increasing with latitude (-0.63 Dobson/year in New Caledonia, with no mass
bleaching reported), but none in the Northern hemisphere summer, even to
the northernmost tropical latitudes (and temperate ones, not shown).
In addition, ozone values are at their highest level in summer in both
hemispheres, May-August in the North and August-December in the South, with
a cross of seasonality pattern around 5oS. The lowest ozone values for the
1979-1991 period always occured in June-August south of 5oS and
November-February north of it. The 20th lowest values are mostly
encountered in northern locations in winters 1983, 1985 and 1988, and in
southern locations in winters 1985, 1990, 1980, and also in summers 1984
and 1987 (when no mass bleaching is reported).
Correlation with bleaching events
I restricted my study to twenty bleaching events for which time of advent
is known within a month (Tab. 2). A first visual inspection quickly
revealed very few low values of ozone for the time of year at time of
bleaching, or within the two months before the event, nor drawdown of
I compared the mininimum and the mean ozone values during either one or two
months before bleaching (using as date the last day indicated or the end of
the month if days were unprecised in references) with the same values for
equivalent periods in 1979-1991. There is no difference with the 1979-1991
mean (range -6.77 to 7.14 Dobson, mean 0.79 plus/minus 4.09 for two months
period). It could always be found another year with lower mean and minimum.
Exceptions are Bahamas, September 1987, and Bermuda, August 1988, where
values are often near the lower range, with about ten days of lowest values
upon the two months period. Only San Blas, Panama, with bleaching in June
1983, shows clearly lowest values during the 1-15 May (257-269 Dobson, mean
263.5 plus/minus 3.4, versus decade 256-293, mean 273.9 plus/minus 7.0),
however within only 1.5 standard deviation for this two weeks.
Transient ozone drawdowns of a few days were quantified by the difference
between the daily data and the centered rectangular moving average on
(best) three weeks, and more precisely, by the square of only negative
value of this difference, emphasizing remarkable low events, also both for
one or two months period before bleaching events. No differences for the
drawdown indexes are noticeable with the 1979-1991 mean (-0.108 to 0.360,
mean -0.078 plus/minus 0.0.363 for the squared index over two months) and
lower minima and means could always be found in other years. Particularly
low values of drawdown indexes associated with bleaching in Jamaica 1987,
Pari 1983 and Looe Key 1983, but are due to jigsaw records from quite high
levels ; and in Lizard island, GBR (event between the 15 December 1981 and
7 January 1982), with a pretty fall of ozone from the 16 to 22 December,
downto 254 Dobsons, i.e. 5 to 15 Dobsons below moving average, but there
are usual falls downto 240-250 Dobsons in December and January. Moreover,
the GBR 1982 event appeared synchronously over 500 km, and ozone values
over the Magnetic and Myrmydon islands areas, though with some
parrallellism, show no drawdown.
Also relevant, bleaching was observed in 1987 in Florida in mid-July at
Looe Key and end-August at Key Largo (Jaap, 1988), whereas the ozone
records are very similar with difference of -1.10 plus/minus 0.85 Dobson,
range -19 to 12, mainly because of a time lag of one day between this two
sites (Fig. 2A).
These results confirm previous analysis of an abscence of trend of ozone in
tropics and extended them for month and seasonal time scales, as well as
for variance and particularly low values.
Ozone level is at its highest in summer when mass bleaching usually occurs.
Its record appears highly variable at annual and interannual scale (ex.
fig. 2A). In fact, the volcano impacts (El Chichon, March 1992, Nevado del
Ruiz, November 1985, Pinatubo, June 1991) are not discernable in the raw
data unless removal of seasonal, ENSO, QBO and 11 years sun cycles (Zerefos
et al., 1992, Herman and McPeters 1993), contrary to a suggestion that
preferential bleaching in 1983, 1986-88 and 1991 might have been due to
those volcanic eruptions (Hallock and Talge, 1993).
The abscence of any trend nor correlation between ozone low and mass
bleaching implicates that UV are not the primary cause of the phenomenon.
An indirect UV effect, due to higher water transparency in reason of a
would-be global increase of doldrum time in tropics was suggested by
Gleason and Wellington (1993). But periods with very calm sea certainly
occur already in the past decades. Moreover, mass bleaching is often
observed in very shallow waters and long term change of irradiation in one
meter depth water or less can be only negligable.
Of course, this does not preclude that UV play is one of the stress,
perhaps important, as shown in situ by UV shielding of large foraminifers
during an event (Hallock and Talge, 1993) or of upward transplanted corals
(Gleason and Wellington, 1993), but just like visible light, probably
involved at the photoinhibition site, the PS II D1 protein Qb site (Friso
et al., 1995, Day and Vogelmann, 1995, and ref. herein).
Large foraminifers, which at contrast to corals continue to calcify during
bleaching, show, even in the stable conditions of front reef facies bathed
by pristine open ocean waters, spectacular shell abnormalities (Pecheux in
Muller et al., 1991, unpublished, Hallock and Talge, 1993, Hallock et al.,
1995), almost unknown in sub-present or geological times (in prep.). This
clearly emphasizes the recent appearance of mass bleaching and its real
signifiance at long term planetary level.
Given bleaching occurance, its explanation must hold for all latitudes and
longitudes in tropics, for all reef biotopes (from 0 to 100 m depth, lagoon
to fore-reef, isolated islands to barriers). It must involved a fundamental
biochemical process, as implicated by the biodiversity of reef
photosynthetic symbioses, exclusively and all affected, symbioses which
constitute the founder of this ecosystem. This excludes complex
regional-differentiated climatic or hydrologic changes origin and lets
ozone depletion and CO2 rise as the only alternatives. Now the UV
hypothesis can be also rejected with good confidence.
As supported by theoritical arguments and preliminary CO2-induced bleaching
experiments (Pecheux, 1993, 1994), the CO2 rise and the acidification of
surface ocean, with H+ actual change of 21%, appears as the responsable
global changing factor. It probably weakens pH-controlled HCO3- uptake by
the host for photosynthesis of symbionts, now critical during maximum
summer stress conditions, with synergy of temperature, irradiance included
UV, and water stagnation. The CO2 rise is now the only last serious
explanation of reef mass bleaching.
Acknowledgement : Thank to M. Lhomme of the Computer Center of the Nice
University for access to CD-ROM units and valuable help. The members of the
TOMS NIMBUS Experiment and Ozone Processing Teams and the National Space
Science Data Center, P.T. Guimaraes, R.D. McPeters, R.D. Krueger, D.E.
Larko have my sincere acknowledgement. This work was supported by French
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Table 1 : Examined reef areas with latitude (negative values South) and
longitude (negative values West) of nearest TOMS grid point, 1979-1991
mean, minimum and maximum ozone values in Dobson, trends in Dobson/year,
correlation coefficient r2 and probability p of linear regressions.
Table 2 : Examined bleaching events : sites, year (Y), month (M) and day
(D) (last day indicated in references or last day of month if unprecised),
mean (Mean), minimum (Min), and maximum (Max) ozone values of two months
period before bleaching, their differences for the same period of year with
the 1979-1991 mean (dM), with the year of lowest mean (dLM) and the minimum
value (dMin), and same differences (dD, dLD, dMin) for a drawdown index
(minus squared of only negative values of difference with three weeks
movering average on one month period before bleaching).
Bleaching events were described in : Great Barrier Reef : Oliver, 1985,
Harriott, 1985, Fisk and Done, 1985, Coffroth et al., 1898 ; Mayotte :
Faure et al., 1984 ; Indonesia : Hoeksema, 1991 ; Galapagos : Robinson,
1985, Glynn, 1989 ; Panama : Lasker et al., 1984, Knowlton, 1988 ;
Venezuela : Losada, 1988 ; Philipine : Yap et al., 1992 ; Puerto Rico :
Goennega and Canals, 1990 ; Jamaica : Woodley, 1988, Sandeman, 1988, Goreau
and MacFarlane, 1990, Goreau, 1990, 1991 ; Japan : Kamezaki and Ui, 1984 ;
Bahamas : Lang et al., 1989 ; Florida : Jaap, 1985, 1988, Te Strake et al.,
1988, Hudson, 1988, Porter et al., 1989 ; Bermuda : Cook et al., 1990.
Fig.1 : Ozone trends in Dobson/year during 1979-1991 versus latitude for
the four seasons, without significance between 15oS and 15oN. Note that no
ozone decrease is observed in summer Northern hemisphere up to 35oN,
whereas it exists in summer Southern hemisphere south of 15oS, of which I
does not have explanation.
Fig. 2: a) Example of an ozone record : Key Largo, Florida, USA. 2A : Note
the great variance at annual and interannual scales. Highest values of
ozone occur during summer. Note lowest values in winter 1985, 1988, 1991.
There were bleaching events in September 1983, August 1987, in autumn 1991,
and more recently in summer 1992 (only large foraminifers) and summer 1993
(Hallock and al., 1995). b) Ozone record around the 1987 bleaching event in
Looe Key in July (continuous line) and Key Largo in August (discontinuous
line), together with minimum and maximum values for same days during
1979-1991. Note coherent values of ozone level over the region, and their
normal level for this year.
>From Editor of the Marine Ecology Progress Series, mainly :
"(...). Your paper may well be publishable in another journal; but, the
work is largely outside the scope of MEPS. (...)".
First reviewer :
"Publication not recommanded. This ms does not pass our usual MEPS
standard. It presents a confusing picture. Global warming does occur and
many bleachings are related to increase seawater temperatures although more
than one causal factor may be involved.
The results, General trends as well as the Correlation with bleaching
events, are confusing without appropriate statistical analysis of data. The
ms is badly written and the contents are not very interesting."
/My commentary : critics not interesting/
Second reviewer (my commentary under //):
"This paper adresses an interesting and important topic but suffers from
careless presentation, and language problems as well as misinterpretation
of the existing literature (see comments on the text).
Contrary to what what is stated in the paper there is good evidence of a
coincidence between extreme El Nino events and bleaching at sites across
the Pacific in 1983 (Glynn 1993) /what I agree in the text for El Nino
1993/. Elevated seawater temperatures are known to result in coral
bleaching both in simulated laboratory experiments (Glynn and D'Croz 1990)
/yes, and many other papers, but as with almost any kind of stress/ and in
the field (Glynn 1994). In the submitted paper the effects of elevated
seawater temperatures are practically ignored /not the subject/.
While the analysis of the satellite derived ozone data is of some interest
it is important to consider other factors which are likely to influence the
bleaching response in shallow waters as a result of increased UVR
penetration. One such is the transparency of seawater at any particular
location and this should be acknwoledged in the text /I can not agree :
long term global change of transparency in very shallow water, for which no
indication is in support, can be only negligeable/. Similarly no
consideration is given to synergistic effects of interacting factors eg.
high seawater and high irradiance /at contrary I conclude that bleaching
appears to be due to CO2 in synergy with temperature, light include UV,
The current analysis has produce negative resuslts which, nonetheless are
important to publish given the body of scientific opinion seeking to
involve UVR as a major factor responsible for coral bleaching. I would
suggest that the author attemps to summarise his finding as a short note
/bof/, eliminates all jargon (eg ozone drawdowns /but it used in
geophysical papers/, jigsaws records etc) and quite simply presents a case
which is based on two figures and a single table. Most importantly it would
be essential to have the draft text checked by an English-speaking
scientist before submission."
Laboratoire de Geodynamique sous marine
Universite Pierre et Marie Curie
La Darse, B-P 48,
Villefranche sur Mer, France
Tel : (33) 93 76 37 40 ou 37 49
Fax : (33) 93 76 37 66
E-mail : micho at ccrv.obs-vlfr.fr
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