[Coral-List] Darwin was WRONG about reef formation

[David Blakeway]

Doug - Their interpretation for the Maldives is that the carbonate sequence
was all produced in shallow water, over the subsiding volcanic plateau.
Deposition rates varied across the plateau, some areas remaining shallow
and other areas drowning. The areas that remained shallow developed into
flat-topped sea-level banks during a long period of relatively stable sea
level just over 3 million years ago. Atoll morphology subsequently
developed over the flat-topped banks, and is therefore independent of the
deeply buried volcanic substrate. I think it is a good model, with some
solid supporting evidence from the Maldives. But the article would be so
much better if it exercised more restraint and balance; e.g. by conceding
that there may be multiple paths to atoll morphology, by acknowledging that
Darwin had already suggested some atolls develop from submerged banks, and
by citing previous work apparently contradictory to their conclusions.

By the way, Darwin's tentative explanation of the Maldives was to slowly
submerge a large elongate island surrounded by a barrier reef, like New
Caledonia. The reef "*...after repeated subsidences, would become during
its upward growth separated into distinct portions; and these portions
would tend to assume an atoll-like structure, from the coral growing with
vigour round their entire circumferences, when freely exposed to an open
sea." *Referring to these sub-atolls, he later says* "...these again,
during long periods of subsidence, would sometimes become dissevered into
smaller atolls.*" I know it is just logic, but sure seems like magic!


On Tue, Oct 27, 2020 at 3:22 AM Dennis Hubbard <dennis.hubbard at oberlin.edu>
wrote:

> Thanks David:
>
> Going back to a thread from a couple years back, this is the reason that
> extensive citing of the literature (and not just the most recent and "hot"
> articles) is so important.
>
> Dennis
>
> On Mon, Oct 26, 2020 at 10:57 AM David Blakeway <
> fathom5marineresearch at gmail.com> wrote:
>
>> The Droxler & Jorry article provides a valuable perspective but, as has
>> been pointed out by others, it sells Darwin short. The article claims that
>> most modern atolls have developed over flat-topped Pliocene banks, and
>> therefore that Darwin’s fringing reef to barrier reef to atoll model is
>> wrong. However, Darwin already knew his model did not apply to all atolls.
>> For example:
>>
>>
>> “*...if, therefore, corals were to grow up from a bank, with a level
>> surface some fathoms submerged, having steep sides and being situated in a
>> deep sea, a reef not to be distinguished from an atoll, might be formed..*.”
>> (Darwin 1842, chapter 5)
>>
>>
>> Furthermore, the article fails to cite a recent paper that describes a
>> fringing reef to barrier reef transition at Tahiti, reconstructed from 35
>> logged and dated cores (Blanchon et al. 2014; open access at
>> https://www.nature.com/articles/srep04997).  Such selective citation is
>> especially disappointing in a review article.
>>
>>
>>
>> An additional problem with the article, from my perspective, is that it
>> invokes the antecedent karst hypothesis to explain the atoll rims. A more
>> parsimonious explanation, developed by the first scientists to survey
>> atolls in the early 17th century, is simply that corals and coralline algae
>> grow better in the turbulent and well-oxygenated water on the outer edges
>> of submerged structures.
>>
>>
>> The karst hypothesis, in my opinion, is impeding coral reef science
>> because it views reefs as passive structures – it denies the reef-building
>> organisms any agency in creating reef form. We really need some young
>> ecologists to take reef geomorphology forward!
>>
>>
>>
>> David Blakeway
>>
>
>
> --
> Dennis Hubbard - Emeritus Professor: Dept of Geology-Oberlin College
> Oberlin OH 44074
> (440) 935-4014
>
> * "When you get on the wrong train.... every stop is the wrong stop"*
>  Benjamin Stein: "*Ludes, A Ballad of the Drug and the Dream*"
>