[Coral-List] Comment on Atoll formation

[Lescinsky, Halard L]

I'd suggest that Ulf, and others who think that most inhabited coral cays are simply the result of incremental build-up of storm debris, should take a look at the recent paper by William Dickinson (2009, GSA Today 4-10; http://www.geosociety.org/gsatoday/archive/19/3/pdf/i1052-5173-19-3-4.pdf ).  A take home message of Dickinson's work is that inhabited cays are generally stabilized or "pinned" by reef deposits that formed during the Mid-Holocene Highstand 4,000 years ago when sea level was a couple meters higher than it is today.  The islands, therefore, owe their existence to exposure and cementation of carbonate during sea-level fall, NOT keep-up style carbonate accretion.  When rising sea-level floods the islands in the near future they will again become uninhabitable, as in fact they were until about 1500 years ago when falling sea-level first exposed them and allowed for their colonization.  ---  Hal Lescinsky



-----Original Message-----
From: coral-list-bounces at coral.aoml.noaa.gov [mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of Ulf Erlingsson
Sent: Wednesday, September 29, 2010 10:13 AM
To: coral-list at coral.aoml.noaa.gov
Subject: Re: [Coral-List] Fw: Chagos MPA - Continuing international dispute overboundaries

Let me point out that the argument that atolls will sink due to sea  
level rise due to global warming fails to take into account the  
geomorphological mechanisms by which atolls are created and grow.  
They grow, slowly, through coral reef growth (as should be no news to  
anyone on this list), through littoral processes, and through  
chemical precipitation, i.e., when the water gets supersaturated with  
respect to CaCO2 the calcium is precipitated in layers on ooid sand  
grains, eventually building up large land masses such as the Bahamas.

The problem is only when the sea level rises quicker than these  
processes can keep up with. However, the predicted rise in sea level  
is much smaller than the quickest and largest sea level rise in the  
recent past. See http://erlingsson.com/authorship/CIS2GOM.html

Of course, that event did drown large areas that are now sea floor,  
but others managed to remain above water. A question of interest is,  
naturally, what lessons we can learn from that event.

Ulf

On 2010-09-28, at 22:41, Douglas Fenner wrote:

> But those same atolls may not be
>  inhabited much longer, due to sea level rise.

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