[Coral-List] relatively new article

Mon Feb 28 16:15:31 UTC 2022

Hi Doiug:

Thanks for your thoughtful post. There are a lot of things to think about
here, and I can't claim to fully understand the linkages that might allow
"deep" corals to replace their shallow counterparts. However, based on my
experiences (mostly in the Caribbean and Western Atlantic), how likely this
might be depends heavily on the large-scale antecedent topography. In the
Caribbean and Gulf of Mexico, there are several broad and flat banks that
sit near 20-30 meters (i.e., there is no emergent landmass nearby). In
these cases, sea-level rise would logically limit recruitment  of anything
on the bank top to deep-water species that can thrive at greater depths
(i.e., there is no "higher ground" to move to as would be the case in a
ramp-like environment). Because the accretion rates of deeper reefs are
already much slower than present SL rise, it seems unlikely that they would
be able to "catch up" as the difference between the rate of SR rise and
reef building (not to be conflated with goral-growth rate) will only
increase.

Dennis

On Mon, Feb 28, 2022 at 9:13 AM Douglas Fenner via Coral-List <
coral-list at coral.aoml.noaa.gov> wrote:

>       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
> > _______________________________________________
> > Coral-List mailing list
> > Coral-List at coral.aoml.noaa.gov
> > https://coral.aoml.noaa.gov/mailman/listinfo/coral-list
> >
> _______________________________________________
> Coral-List mailing list
> Coral-List at coral.aoml.noaa.gov
> https://coral.aoml.noaa.gov/mailman/listinfo/coral-list

-- 
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"*
 Benjamin Stein: "*Ludes, A Ballad of the Drug and the Dream*"