buddrw at kgs.ukans.edu
Sat Sep 15 17:10:42 EDT 2001
<riskmj at mcmail.cis.mcmaster.ca>, Jim Hendee <hendee at aoml.noaa.gov>
Subject: RE: coral reefs doomed?
Sender: owner-coral-list at coral.aoml.noaa.gov
It's interesting, if mildly depressing, to see so many reasons for pessimism.
I generally agree with most of Mike's points, but there are two that he
raises that I think merit comment -- both related to the CO2 and
saturation state issue, and both addressing issues of temporal scale and
First, Mike raises the question of 'long-term' silicate buffering. True
enough -- in the very long term, none of this is an issue, and even on the
thousands of years time scale we are dealing with ocean DIC content that
overwhelms the size of the atmospheric reservoir(and essentially all
others but the mineral). The critical issue is that we are not dealing
with scales of this magnitude -- the anthropogenic CO2 input has been on
the scale of a century (more if you count the beginning of the industrial
revolution, less if you start from the rapid rise post-WWII). The mixed
layer of the ocean, however, contains DIC in an amount comparable to the
atmospheric reservoir with a probably turnover time of a few centuries
(cf. many radiocarbon studies of marine apparent ages). For the purpose
of considering presewnt problems, it is a reasonable first approximation
to treat the mixed layer (which is where all of the reef-building corals
live) as an isolated compartment, and on that scale the CO2 effect is
Second, the high-mag calcite issue -- I too am out of my office, but in
1986 June Oberdorfer and I published a chapter in Carbonate Diagensis book
edited by Purser and Schroeder that pointed out that reef interstitial
water is controlled at the saturation state of high-mag calcite. What is
most definitely not true is that this has much effect on the saturation
state of the overlying seawater. Here again, the issue is time scales --
in this case of advective open water exchange compared to the flushing of
interstitial porewaters (see also the paper by same authors in the ICRS 6
proceedings). There are many orders of magnitude difference -- and in
fact the possibility of equilibrating the sedimentary carbonate with the
ocean water is on time scales equivalent to the silicate buffer controls,
and basically insignificant on the 100 year scales dominated by gas and
open water exchange reactions.
A question, Mike -- I didn't understand your point about vertical mixing
replacing high pH bottom water with low pH suface water -- did that refer
to some particular locale? Certainly for most of the ocean saturation
state, pH etc are lower at depth than at the surface.
>===== Original Message From "Mike Risk" <riskmj at mcmail.cis.mcmaster.ca> =====
>Although I share your concerns in general, the bad news is: the conclusion
>is probably correct. I don't read that as a funding ploy-Rupert clearly says
>there's stuff-all we can do about it, leading funding agencies to say why
>Notwithstanding the recent stimulating work by Jackson et al on overfishing,
>the hard evidence from the 20th century (and this one, too) is that
>land-based sources of pollution have ineradicably slain more coral reefs
>than all other causes put together. The references on this are close to
>countless. This trend continues unabated, and science seems slow to respond.
>(I invite other readers, perhaps offended by this comment, to submit
>examples of coral reef monitoring programs that are linked to legislation
>and enforcement by a proper detection/identification/amelioration process.)
>Will reefs colonise new shelf areas? Sure. In fact, the rate at which this
>will occur may be estimated from the drilling work done long ago by Walter
>Adey, in the Virgin Islands. It takes the ocean about 1,000 years to clean
>up the shoreline and make it ready for new corals. Presumably, this same
>process in the future will take even longer, given the necessity for
>reworking condos and Hondas: plus, that ocean will not be nearly as clean as
>the advancing Holocene seas were. So: but don't hold your breath. For sure,
>it will happen after the next election.
>Concern about ocean warming is well-placed. One of the best references to
>this is by Francis Rougerie, in...1988?. This is in French, and hence not as
>widely read and cited as it should be. Quelle honte.
>Concern about oceanic pH is probably overblown:
> 1. we seem to have forgotten the seminal work of Sillen, in the 60's,
>showing that silicates, not carbonates, are the long-term oceanic buffers.
>Lord knows we have done lots to "protect" tropical coastlines from pH change
>by loading them with chemically-reactive silicates (feldspars, illite,
>montmorillonite, etc). Large quantities of these minerals are in fact bound
>up in coral skeletons, hence corals carry with them their own personal
>buffers (Cortes and Risk, 1985, BMS).
> 2. the pH of tropical coastlines will no doubt shift-after all the
>high-mag calcite has dissolved. As HMC makes up a large proportion of reef
>sediments, this may take some time.
> 3. as the climate changes and we shift to the other metastable condition
>of global climate, this will be accompanied by a fundamental reorganisation
>of the oceans. This will involve (far as we know) vertical mixing, which
>will put low-pH surface waters into contact with bottom sediments and bottom
>waters of higher pH. This process was outlined in Smith et al, 1997, April
>Nature. This process can occur within five years. None of the present ocean
>models allows for mixing on this vertical and temporal scale, hence all need
>recalibration. (Some of this work is under way now, using data from
> 4. McConnaughey and colleagues, and Barnes and colleagues, in separate
>publications within the last 12 months, have shown that corals calcify
>faster at elevated temps, and in the presence of fleshy algae.
>My prediction (Risk, 1999) was that coral reefs, as some of us knew them
>(and you were one, Jim), will be eradicated by land-based sources from most
>of the world's shelves long before pH shifts appreciably-in fact, my
>prediction was even more dismal than Rupert's. I think I said 2020.
>I am hesitant about statements, usually made (I'm afraid) by geologists,
>along the lines of "Corals have been around for a long time, they will
>survive." It's true, but misleading. Yes, coral relatives-burrowing sea
>anemones-are the oldest metazoan fossils yet found: Proterozoic, McKenzie
>Mountains, NWT. Such statements need to have appended to them the comment
>that large proportions of the geologic record are virtually barren of reefs,
>of any type. I consider these statements similar to: "The globe's been hot
>before, we survived", which we have also heard lately. The globe has been
>quite hot before, involving a fundamental rethinking of real estate values.
>Every North American Grade Six kid should do the exercise of drawing the
>+15-m sealevel contour onto the globe, and estimating the human population
>involved. Or perhaps we should start with those politicians whose
>development seems to have been arrested at Grade 6...
>It may very well be that some of those we refer to as "deep-water" corals
>may be a recolonisation/biodiversity resource-let us hope so. This has
>recently become an extremely productive area of research, and interested
>persons should log on to the coolcoral site, or contact me for preprints.
>This email is devoid of specific page #'s, etc, for refs: my office is being
>moved, I am fileless, and am celebrating by being a carpenter for a while.
>Another guy who tried it came back, so what have I got to lose?
>Yours in gloom: Mike
>For directions on subscribing and unsubscribing to coral-list or the
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Dr. Robert W. Buddemeier
Senior Scientist, Geohydrology
Kansas Geological Survey
University of Kansas
1930 Constant Avenue
Lawrence, KS 66047
ph (785) 864-2112; fax (785) 864-5317
email: buddrw at kgs.ukans.edu
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