coral reefs doomed for sure.
riskmj at mcmail.cis.mcmaster.ca
Thu Sep 27 22:02:02 EDT 2001
Bob, List-Some comments re the general discussion of changes in alkalinity,
dooming of reefs, etc.
Some of the following builds on previous postings on this list, and some
amounts to a Discussion of the Kleypas et al 1999 Science paper. I was going
to write a formal Reply to this, never got around to it...
In general, my reservations about some of your positions are based on my
belief that there has been insufficient consideration of two of the big
Bio's in reef science: bioturbation and bioerosion. In addition, I have
reservations about some of the chemical models/assumptions.
1. Bioerosion. The first quantitative work on the importance of bioerosion
was published so long ago only me and Hendee were alive. Since then, there
have been several large, exhaustive and exhausting studies of this signal
process, and they have all come up with the same answer: on "normal" reefs,
bioerosion and calcification are in approximate balance. On most fringing
reefs, subject to increasing terrestrial nutrient input, therefore, the
balance has already been shifted towards destructive processes. I will cite
no references here. Knowledge of bioerosion should be an integral part of
every reef scientist's knowledge base. In short, looking at corals is way
less than half the picture: you should all know this.
Unfortunately, this field seems to have fallen off the radar screen in the
past few years: in the Amer. Zool. 1999 volume, for example, the word does
not appear once. (Stop for a moment, and think of the gaping hole in our
understanding that this reflects...) If it weren't for the French, there
would be virtually no ongoing research on this process. (Salud, mes
amis...et amies.) Any "reef monitoring" program that does not include
assessment of bioerosion is a colossal waste of money-and I know of only one
that does. Not only does this ignore most of the action-it excludes some
Any "reef model" that does not include it...it's hard to be polite, here.
These models would better be termed "Less-than-half-of-the-reef models."
2. Bioturbation. Again, an exhaustive literature-lagoon and shelf sediments
are vertically mixed on a timescale measured in months. Any number of
critters involved here, of which the front-runners (in the Cenozoic) would
be the thalassinid shrimp.
3. Oceanic/Climate Models. Notwithstanding their protestations to the
contrary, I have found modellers to be resistant to data that upset their
models, with that resistance being directly proportional to the amount of
federal money invested to date. "One major problem with the current
generation of GCM's is that the treatment of ocean circulation is still very
crude." (Ruddiman, 2001: Earth's Climate).
The implications of Smith et al, 1997, are that a meltwater pulse can divert
or shut down the Gulf Stream in less than 5 years. To all of you out there:
when the oceanic part of GCM's can model this, then start believing them-not
before. The strong compartmentalisation of the mixed layer to which Bob
refers is metastable, and temporary.
4. The Magnesium Salvation Theory-sort of reads like a cure for
constipation, doesn't it? Stick to science, Mike.
While I concur with some of what Bob says here, re porosity of reefs and
reef sediments, I am not wholly persuaded:
-"...high magnesian calcites are dissolved preferentially in these
sediments, although the sediment contains a mixture of (all types of
carbonates). In deposits composed primarily of red algae, this early
diagenetic reaction has resulted in dissolution of 75% of the carbonate."
(Morse and Mackenzie, 1990: Geochem of sedimentary carbonates).
-"The data indicate that all samples are very close to equilibrium with
Mg-calcite....alkalinity shifts relative to sea water indicate that initial
precipitation may be followed by gradual dissolution in response to CO2
added..." (Buddemeier and Oberdorfer, 1986).
-etc etc. And finally, Bob Halley and his USGS colleagues have done some
very nice experimental work, some of which was reported in Bali, showing
that, indeed, HMC dissolves.
As far as the large inventory of HMC being buried-I think Callianassa and
its cohorts have a great deal to say about that. Ain't going to happen. The
sediments that reefs will produce in future, moreover, will likely be lower
in relative concentration of HMC. The main contributors of HMC are the
calcareous algae-CCA. As we eat the grazing fishes, and the urchins die off,
and fleshy algae bloom in eutrophied coastal waters-reef seds will likely be
higher in organics and lower in HMC.
Some other points, perhaps more peripheral: high pH's have been recorded
inside coral heads-indeed, pH's at which silicates are very unstable (Risk
and Muller, Middle Holocene, Limnol. Oceanogr.-give me a break, I have only
unpacked the first of 20 boxes of books). This will triggger dissolution of
reactive silicates-in fact, the pH inside corals probably shifts 3-4 full
units, making possible all sorts of neat chemistry. Don't forget, the
sediments being delivered to the world's coastlines now are very different
from pre-agricultural times. Now, we see reactive silicates-andesitic ash
from 5-year-old falls, delivered to the coastline by rivers, may be seen
hydrating and dissolving under 10-odd cm of carbonate sediments, at several
locales in Indoensia. This is not a millenial timescale.
So, in short, Kleypas et al:
1. depends on reef models that ignore >50% of the process
2. depends on outmoded oceanic circulation models
3. ignores some fundamental chemical questions.
Other than that-we have to admit that it was an important paper, because it
has stimulated a great deal of discussion. From that standpoint,
congratulations to the authors. (Most of my papers disappear as neatly and
as quickly-and as deeply- as Olympic springboard divers.)
My main concern with that paper is that it may have diverted intellectual
and financial resources from more pressing problems. Sure, changes in
saturation state will eventually affect....what? What will be left, in say
100 years? pH changes in the ocean, in my opinion, don't make the Top Twenty
Reef Threats. The rate of present destruction from land-based sources and
overfishing simply dwarfs everything else.
But we have three predictions running, now: I say (something like) "reefs,
as some of us knew them, will be gone from most coastlines by 2020." Rupert
Ormond says 50 years. Kleypas et al say a century. I hope to God they are
right-but I don't think so. In fact, the reason I felt able to make that
dire duo-decadal forecast is: it's already come true.
I hesitate to enter the discussion about ABH-not because of ignorance (that
has not worked in the past), but because Ove's doing a pretty good job
stirring this pot. It seems to me that there might be some help, again, in
the fossil record. One would assume that corals would adapt to rising
temperatures (perhaps better than falling ones?). I am afraid, however, that
my knowledge of the record isn't good enough, nor are the temperature data.
Sea-surface temperatures are believed to have gone well above 30 in the
Mid-Cretaceous, and mid-Cretaceous "reefs" (piles of rudists, really) are
very low in corals...but this is far from conclusive. Perhaps one could look
more closely at rudists, which had zooxanthellae, same as does
Tridacna...corals, of course, have had zoox since the Paleozoic (Risk et al,
Early Holocene, same excuse).
The other problem with the record is the paleotemperatures. Planktonic
forams give excellent results, for the open ocean. We really need shelf
data-but many reports in the literature of paleotemperatures from benthic
shelf critters are just not dependable. The problem is, the six people in
the world who really understand KIE don't publish enough, and those that
don't, publish too much. So this remains an open, and intriguing, question.
On another note: I have to apologise to the List for exposing some of my
personal affairs. That was forgivable only given my state of mind at the
time. Nonetheless, several people whom I had never met sent condolences and
best wishes! So-thank you, and it will never happen again.
She has gone from
liquid food-IV drip, to
liquid food-juices, to
solid food-mushy stuff, to
liquid food-gin and tonics. So recovery is well under way.
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