[Coral-List] Comment on Atoll formation

Chip Fletcher fletcher at soest.hawaii.edu
Thu Sep 30 14:13:13 EDT 2010

Re: Atolls and rising seas 
Sea level inundation in Micronesia (western equatorial Pacific) is already
threatening the livability of atoll islets. By the time Dickinson's atolls
(a great paper, by the way) become "unpinned" in the second half of the
century, islets will have likely been uninhabited for decades. The process
is underway now. Over 2006-2009 inundation associated with extreme tides
(known locally as "king tides") eroded shorelines and damaged soil,
agro-forestry, and groundwater throughout Micronesia. Without emergency
water and food many islet communities would have had to abandon their lands.
These events were so alarming that the Federated States of Micronesia
declared a national state of emergency on Dec 30, 2008. If inundation events
persist with any regularity in the coming decade, we may see a significant
emigration of atoll communities. Generally high water in the western Pacific
since 1998 (satellite altimetry indicates SLR of 5-10 mm/yr in the region)
may reflect decadal processes, and it may be too early to definitively say
this the signature of global warming. Nonetheless, the regionally rapid SLR
provides a glimpse of processes in a warming world; and it would be prudent
to prepare for more of the same...Chip Fletcher, Hawaii

-----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: Thursday, September 30, 2010 3:26 AM
To: Coral-List at coral.aoml.noaa.gov
Subject: Re: [Coral-List] Comment on Atoll formation

I took a look at that paper and note that he has a VERY generic sea  
level curve, referenced to Clark et al (2004) which I don't have  
access to. However, the 2004 article deals with the sudden sea level  
rise at 19000 before present, not a Holocene maximum. Dickinson  
SHOULD have made reference to an article that explicitly investigated  
the Holocene sea level ATA THAT SITE. As it stands, the conclusion  
rests on loose sand. It could equally well be wrong as right.

On 2010-09-29, at 17:40, Lescinsky, Halard L wrote:

> 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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