[Coral-List] relatively new article

Douglas Fenner douglasfennertassi at gmail.com
Sun Feb 27 22:32:33 UTC 2022


      The article I posted about actually says that there is minimal
overlap in the coral species in American Samoa between the coral reef above
30 m deep and the mesophotic reef.  That means there is a limited
opportunity for an effective deep refuge for corals here, even if all the
other things were in place to make it possible, such as larvae from deep
arriving in shallow to replace dead shallow colonies, deep coral genetics
that allows those their larvae to survive and grow in shallow water, and
maybe a few other things.
      Yes, I was reading that the US east coast had much more rapidly
rising sea levels than elsewhere.  Notice that all the sea level graphs the
article Mike points us to are from the US east coast and Gulf coast.  I
believe that rise has to be because at some depth in that area, water has
warmed, which I presume would have to be due to the sinking of water that
was warmer than has been sinking in the past (the sun only heats the
surface of the water).  Most of the water that sinks to the deep sea is in
Antarctica and in the north Atlantic, I believe.  Water expands very
slightly when it warms.  So strange as it may seem, locally slightly warmer
deep water can cause faster local rises than the global average (a local
sea surface bulge).  Or maybe currents are pushing the water higher.  Last
I knew, the average global sea level rise rate was up from 3 mm/yr to about
4.5 mm/yr.  Well within the range of growth rates for coral reefs.  Most of
the world's coral reefs are not on the US east coast, in fact the only ones
on the US east coast are at the far southern end at the southern tip of
Florida.  And the US Gulf Coast has precious few reefs.  Most of the
world's reefs are far from that, in places like the Coral Triangle and the
Pacific Ocean.
       Clearly, the rate of sea-level rise is increasing, and it is certain
to accelerate in the future.  Exactly how fast it will go is a difficult
thing to predict, much of the ice in a place like the West Antarctic may,
or may not, start sliding off faster if the Thwaites glacier becomes
ungrounded where it floats as an ice sheet, or simply having the ice sheet
break off will let it start sliding off much faster.  It won't slide off in
a flash, but the rate of sliding off could go up significantly, and surely
will at some point in the future, but maybe not very soon, hard to predict
they say.  But the science is surely getting better all the time.
       So over the longer period of time, you're surely right.  Over
shorter time spans it is much more open.  Over a couple decades, I doubt
sea level rise is going to outpace the growth of many coral reefs.  And
when it does, it will simply provide more accommodation space, that is,
water above it, that coral can grow into.  Even at 4.5 mm a year, with
staghorns and tables able to grow 100 mm a year and massive corals able to
grow around 10 mm a year, most corals can grow as fast or faster than
sea-level rise.  Because corals don't cover the entire surface of the reef,
the reef can't grow as fast as the corals.  But if the sea level rise would
just hurry up, corals could grow much more on reef flats and have higher
coral cover and thus reef flats could grow upward faster than they do now
(but only where there isn't heavy terrestrial sediment).  Reef flats
typically have low coral cover, boosting it to high coral cover would speed
reef growth rate.  If global warming and bleaching didn't kill corals, it
would benefit most of the world's reefs, reef flats would have higher coral
cover since the lowest tides of the year wouldn't be killing the coral, and
with higher coral cover, the reef itself could grow upward faster (and more
live coral on the reef flat would reduce shoreline erosion).  Sadly, we
won't see that because global warming-produced bleaching is going to kill
most of the corals before the water gets deep enough to make much of any
difference.
      Sea level rise relative to land in American Samoa is currently going
faster than the world average as well.  This is because the 2009 earthquake
south of us near the Tonga Trench released stresses that were helping to
hold American Samoa about 40 cm higher than it would otherwise be.
Immediately after the earthquake the islands began to subside, and so far
they've gone down about 20 cm if I remember, and this should slow down and
stop at about 40 cm drop, it is predicted.  But if I go out on the reef
flats, I can't tell the difference.  It sure doesn't look to me like there
is 20 cm more water on the reef flats here currently.  Sea level rise has
to go faster than that to get ahead of the corals.
     Of course, when (it is not "if" it is "when") mass coral bleaching
kills most of the corals, as it is predicted to start doing in 2-3 decades,
then the reefs will not be able to grow much faster than crustose coralline
algae, maybe around 1 mm a year and game over, sea level rise wins and
corals and humanity loses.  But note, corals lose because of mass coral
bleaching, and the reef geological structures will still be there.  Even
coralline algae will lose, global warming is much less likely to kill it
than corals, but it is more sensitive to acidification than corals.  Seems
inevitable, sooner or later.
      And of course, the geological reef structures will still be there and
barely any deeper than they were before.  Corals can grow well down to
around 30 m deep, some much deeper.  Sea level rise would have to be 30 m
before all reefs would be drowned below the level at which if there are
living corals, they can continue to grow the reef structure.  At 10 mm/yr
sea level rise, that would take 3000 yrs to reach a total of 30 m sea-level
rise.  My understanding is that even if we stop emitting all greenhouse
gases tomorrow. sea-level rise will not only continue, it will continue to
accelerate for some time to come, and sea-level rise will continue for
millennia.  Because the world is warmer.  To stop that from happening would
require removing CO2 from the atmosphere.  Trees and other plants are very
good at doing that, but humans are very good at causing deforestation and
not leaving the carbon sequestered in the wood.  Surfaces of rocks exposed
to air for the first time, typically where erosion is happening rapidly,
WILL eventually stabilize CO2, I've been led to believe.  But that
will/would take more than millennia, maybe millions of years (?)
     So, if humanity were to get its act together and stop emitting CO2 and
allow forests and other plant life to sequester carbon, global warming
could stop and temperatures could even start to come down and sea-level
rise slow.  IF (IF!!) coral species haven't been driven to extinction, then
they could start to repopulate those geological reef structures and rebuild
coral reef ecosystems.  It's a dream, not impossible, but given what a
lousy job humanity is doing so far, sure seems like a pipe dream to me.  As
one line in the musical/movie "South Pacific" put it, "if you no got a
dream, how you gonna have a dream come true?"
     But for the foreseeable future, I agree with you.   Cheers, Doug



On Sat, Feb 26, 2022 at 8:45 AM Risk, Michael <riskmj at mcmaster.ca> wrote:

> Not going to happen, Doug. Sea level rise, now 11mm/yr, is already above
> the ability of reefs to keep up. Bandaids won't suffice.
> https://tamino.wordpress.com/2022/02/23/sea-level-denial/
> <https://tamino.wordpress.com/2022/02/23/sea-level-denial/>
> Sea Level Denial | Open Mind
> <https://tamino.wordpress.com/2022/02/23/sea-level-denial/>
> Back in 2010, the North Carolina's Coastal Resource Commission published
> the North Carolina Sea Level Rise Assessment Report. Dave Burton of "NC-20"
> (a trade group for business interests in the coastal counties of NC)
> ridiculed their results, claiming that the only sensible way to forecast
> future sea level rise was to fit a straight line…
> tamino.wordpress.com
>
> ------------------------------
> *From:* Coral-List <coral-list-bounces at coral.aoml.noaa.gov> on behalf of
> Douglas Fenner via Coral-List <coral-list at coral.aoml.noaa.gov>
> *Sent:* Saturday, February 26, 2022 2:37 AM
> *To:* coral list <coral-list at coral.aoml.noaa.gov>
> *Subject:* [Coral-List] relatively new article
>
> deep reef refuge hypothesis
>
> https://www.nature.com/articles/s41598-021-03128-8
>
> Open-access
>
> Cheers, Doug
>
> --
> Douglas Fenner
> Lynker Technologies, LLC, Contractor
> NOAA Fisheries Service
> Pacific Islands Regional Office
> Honolulu
> and:
> Coral Reef Consulting
> PO Box 997390
> Pago Pago, American Samoa 96799-6298  USA
>
> Over 1 million sq km more land cleared for crops
>
> https://www.science.org/content/article/cropland-has-gobbled-over-1-million-square-kilometers-earth-s-surface
>
> Peat bogs hold TWICE as much carbon as the world's forests!!!
>
> https://www.yahoo.com/news/environmentalists-fight-protect-peat-bogs-233902101.html
>
> Slashing emissions by 2050 isn't enough.  We can bring temperatures down
> now.
>
> https://www.washingtonpost.com/outlook/climate-deadlines-super-pollutants-hfcs-methane/2021/04/15/acb8c612-9d7d-11eb-b7a8-014b14aeb9e4_story.html
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