[Coral-List] Newly discovered reef

Fri Nov 6 23:01:23 UTC 2020

Gene,
    What you write about how the modern coral reefs are thin accumulations
on top of older formations, fits with what I've read a number of other
places.  You say that in Florida they are on top of older coral.  I think
of Enewetok Atoll in the Marshall Is. where the first drill hole was
drilled all the way down nearly a mile to the underlying volcanic rock
which I assume was basalt.  So nearly a mile thick of carbonate.  Surely on
Einewetok, the recent coral reef is a thin layer just like in Florida and
the Great Barrier Reef.  But it is on a very thick layer of carbonates,
which I presume are predominantly coral reef material, I believe there is
evidence deep in the core of exposure to air (some terrestrial items, maybe
seeds?).  So some portion, maybe a lot, of that mile thick carbonate is
coral reef which was alive in shallow water at an earlier time.  I presume
a similar situation in Florida and the Great Barrier Reef, though I don't
know how far down carbonates extend and whether it is all coral reef
material.  But when people say "the reef is very thin" it seems to me that
what they are saying is that the most recent layer of reef is very thin,
with reef below it deposited much earlier at a previous sea level high
stand likely.  A very thick accumulation like that at Enewetok which has 60
million year old carbonate at the bottom, is likely a very long sequence of
reef growth layers piled on top of each other.  Saying that the reef is
very thin could lead people to think the whole reef accumulation is thin,
which obviously is not the case.  Instead it is the case that periods of
active reef growth are interspersed with periods without reef growth, but
that it is a stack of many reef growth periods.  If a person wanted to say
the whole thing was "a reef" that wouldn't be far from the truth would it?
Though it could mislead people into thinking reef growth was continuous,
which it was not.  On the other hand, the thin most recent coral reef
construction is on top of a whole deep pile of previous coral reef
constructions and the whole thing could be considered a "coral reef".  Or
could it?
     Does this make any sense?  Have I gone astray?   Thanks!  Cheers,  Doug

On Fri, Nov 6, 2020 at 10:38 AM Eugene Shinn via Coral-List <
coral-list at coral.aoml.noaa.gov> wrote:

> Thank you Alina for setting the record straight as you often do. There
> are few of us old timers left as new profs and students begin
> rediscovering coral reefs. I wonder who still maintains a reprint
> collection of the older papers? My collection was extensive but just
> before COVID struck I changed offices and was encouraged to discard my
> older reprints. They would not fit in my new smaller office. I dumped 25
> file drawers (nearly a ton of precious reprints.)
>
> Yes, that article about the “newly discovered coral reef” made the
> papershere as well as elsewhere. Yes Alina, it has to be a guyot. If not
> a guyot then a piece of the Great Barrier reef. How many young reef
> worker know that even the Great Barrier Reef consists of a thin skin of
> Holocene buildup over a Tertiary substrate. The thickest coral buildups
> (up to around 300 ft thick) are patch reefs growing in the deep lagoon
> behind the Great Barrier Reef.The barrier it self, like our Florida Keys
> reefs are composed of thin coral build ups.
>
> I began spearfishing on the Florida reefs as a teenager in the early
> 1950s. Everything looked like a coral reef to me. However, in recent
> years after doing extensive coring and seismic surveys with the USGS we
> discovered vast stretches of the so-called Florida Keys reefs are
> actually exposed Pleistocene coral buildups that formed 125,000 years
> ago. They were then exposed by a huge drop in sea level until between
> 6,000 and 7,000 when Holocene sea level world-wide began rising over the
> dead reefs. Only in those places (mainly named reefs with lighthouses)
> growing over previous topographic highs(created by Pleistocene coral)
> did Holocene reefs grow thicker (up to 30 -40 ft. thick) And even in
> those reefs, for example Molasses Reef which is one of the most famous
> coral reefs in the Keys, the thin layer of sand in the groves between
> the Holocene coral spurs directly overlies Pleistocene coral. Similar to
> the Australian coral reef, the thickest reefs in the Keys consist of
> patches in the lagoon area behind the linear outer reefs that have spurs
> and grooves on their seaward sides. Of course our lagoon areas behind
> the outer reef chain are no where near the depths found behind the
> Australian Barrier Reef.
>
> Some years ago I did a mission in the Aquarius underwater habitat which
> is situated seaward of the main outer reef line and lies in 50-55 ft of
> water. With support from divers lowering equipment from the surface,
> Jack Kindinger and I core drilled down through 49 feet of coral. What
> did we find? Roughly 6 inches of Holocene (mainly a crust of laminated
> red brown caliche. (Caliche forms on dry land) The remainder of the 49
> ft core consisted of Pleistocene head corals. We had expected to find
> /Acropora palmata/ but found none. This remains a mystery to be solved.
> In all cases our cores showed the outer Florida reef tract is underlain
> by Pleistocene head corals like that supporting the underwater habitat.
>
> In more recent years Toth, et al. (2018) at the USGS St Petersburg
> office carbon dated our USGS collection of coral cores and determined
> that the outer Florida coral reefshutdown 3,000 years ago.
>
> I am reminded of this every time I read a new article about efforts to
> transplant corals to our now mostly dead coral reefs. That the main
> builders are no longer building coral reefs does not mean they are no
> long prime dive sites. There are still sponges, sea whips, fans,
> coraline algae, etc., and beautiful schools of fish and many
> invertebrates. Go diving with tourists and listen to what they talk
> about. It’s the Fish! The key element is clear Gulfstream water that
> allows tourist divers to observe these colorful wonders. Although
> transplanting may be futile, especially in our life-time, the research
> involved is causing coral scientists to learn more about the secretes of
> what corals require to remain alive. Hopefully we will learn why corals
> began dying 3,000 years ago. Gene
>
> --
> No Rocks, No Water, No Ecosystem (EAS)
> ------------------------------------ -----------------------------------
> E. A. Shinn, Courtesy Professor
> University of South Florida
> College of Marine Science Room 221A
> 140 Seventh Avenue South
> St. Petersburg, FL 33701
> <eugeneshinn at mail.usf.edu>
> Tel 727 553-1158
> ---------------------------------- -----------------------------------
>
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