[Coral-List] coral bleaching

Dennis Hubbard dennis.hubbard at oberlin.edu
Wed Apr 20 14:26:30 UTC 2022

Hi Gene:

While the specifics have faded in my memory, "natural" sea level is the
result of many factors including the obliquity of Earth's orbit, Earth's
tilt and its proximity to the sun (probably others that I've omitted due to
failing memory since I taught these things). However, as I remember, both
the magnitude and slope of temperature changes were much smaller than what
we have seen since the "industrial revolution". So, we are, at the very
least" "among" the leading causes. Absolute temperatures have been higher
in the past than what is proposed, but I believe that these intervals
represent significant declines or absence of reefs as wew define them.


On Wed, Apr 20, 2022 at 8:08 AM Eugene Shinn via Coral-List <
coral-list at coral.aoml.noaa.gov> wrote:

> Regarding our recent discussions concerning coral bleaching and
> temperature here is something I thought would be relevant for readers of
> the list. It is well known that the Florida Keys were once a coral reef
> as were many elevated Pleistocene age coral reefs around the planet.
> They had to be formed when sea level was several meters above present.
> They did not grow in air. They grew during what is known as isotope
> stage 5e. The newest information suggests that was 129-116 thousand
> years ago. Most scientists agree the higher sea level at that time was
> due to melting polar ice and therefore Earth was likely warmer that
> today's temperature. If bleaching today is due to warm temperatures,
> then coral growth that produced those elevated stage 5e coral reefs
> should have bleached. We have no way of knowing for sure, but it is
> evident that those 5e reefs did produce what is now land in many places
> including the Florida Keys. If there was bleaching back then it is clear
> those corals did not go extinct until sea level dropped and left them
> high and dry. As readers know, sea level dropped as much as 120 meters
> when those reefs were left high and dry. Sea level then began rising as
> it is doing now. Was the higher sea level during stage 5e caused by
> higher CO2 levels? If so, what caused the high CO2 levels? There were no
> automobiles or fossil fuel power plants back then. The CO2 could have
> been expelled by a warming sea but what caused the sea to warm? Could
> whatever cause the sea to warm be what is causing today's warming? I
> thought these questions would be relevant subjects for discussion by
> members of the coral-list. Gene
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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"*
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