It seems that the scientists calculating sea level rise have a number of conflicting opinions. The original comment in the post was meant as support to the statement that an immediate 20 m sea level rise is highly unlikely, because of the corals, but also because an unrealistic amount of energy would be required, and that such a flood would cause massive onshore erosion that hasn't been observed. 5 m per decennium, century or millennium is still much less than 20 m in an instant. Thanks for sharing your insights.
Hi Betz12345, thanks for your interest. There are numerous articles describing coral reef growth rates during the last deglaciation. For example, https://www.nature.com/articles/s41467-017-00966-x, describe a growth rate of 5-6 m per millennium, and the sea-level rise curve commonly used https://dlab.epfl.ch/wikispeedia/wpcd/images/119/11900.png.htm is based on coral reef growth rates . All these coral reefs survived. To my knowledge no serious study proposed a sudden 20+ m sea level rise. Such a sudden, 20 m sea-level rise is therefore a hypothetical. If it had happened globally then most coral reef systems would have perished.
Thanks, I followed some citations of your first paper (Khanna et al, 2017) and found others interpreted their results as consistent with 5 m/decade sea level rise:
> "Coralgal reef terraces offshore central Texas record punctuated sea-level events of around 5 m to 6 m magnitude over decadal to century timescales between ca. 15.5 ka and ca. 11.5 ka (Khanna et al., 2017)"
Then I looked into some of the assumptions being made and found (amongst other issues) coral reefs have been observed to survive from a few meters up to 160 m depth:
> "One of the main causes for recognition of the greater depth-vari ability of coral taxa has been the routine inclusion of deep-diving and ROV surveys in coral ecological studies over the past few decades, which has broken through the “shallow-water” bias of early surveys by adding frequent observations on deeper occurrences (although more are needed).
[...]
The amount of light received by corals varies spatially and tempora lly, and is influenced by cloud cover, turbidity, tidal changes, reef topography, and depth. The depth of light penetration varies with latitude and distance from the shore (Kleypas et al., 1999), with many coastal reefs receiving reduced light levels due to high turbidity. For example, in the most turbid regions of the Great Barrier Reef, corals are found only within the upper 3 to 4 m of the water column, while on the outer shelf, corals are found to depths up to 100 m (van Woesik and Done 1997, Hopley, 1994, Cooper et al., 2007). At some mid-ocean Pacific atolls, irradiance levels can be compatible with coral growth even at ~160 m depth (Montaggioni, 2005)."
> Corals live in symbiosis with Zooxanthellae, photosynthetic organisms that need sunlight to survive, so a sudden deepening of more than 20 m would have killed off large amounts of Zooxanthellae and their coral hosts, leading to a coral mega-extinction, which is not in evidence.
Interesting idea, can you describe what evidence you looked for?
It seems that the scientists calculating sea level rise have a number of conflicting opinions. The original comment in the post was meant as support to the statement that an immediate 20 m sea level rise is highly unlikely, because of the corals, but also because an unrealistic amount of energy would be required, and that such a flood would cause massive onshore erosion that hasn't been observed. 5 m per decennium, century or millennium is still much less than 20 m in an instant. Thanks for sharing your insights.
Hi Betz12345, thanks for your interest. There are numerous articles describing coral reef growth rates during the last deglaciation. For example, https://www.nature.com/articles/s41467-017-00966-x, describe a growth rate of 5-6 m per millennium, and the sea-level rise curve commonly used https://dlab.epfl.ch/wikispeedia/wpcd/images/119/11900.png.htm is based on coral reef growth rates . All these coral reefs survived. To my knowledge no serious study proposed a sudden 20+ m sea level rise. Such a sudden, 20 m sea-level rise is therefore a hypothetical. If it had happened globally then most coral reef systems would have perished.
Thanks, I followed some citations of your first paper (Khanna et al, 2017) and found others interpreted their results as consistent with 5 m/decade sea level rise:
> "Coralgal reef terraces offshore central Texas record punctuated sea-level events of around 5 m to 6 m magnitude over decadal to century timescales between ca. 15.5 ka and ca. 11.5 ka (Khanna et al., 2017)"
https://pubs.geoscienceworld.org/gsa/books/monograph/2361/chapter/1
33567225/Holocene-Evolution-of-the-Western-Louisiana-Texas
Then I looked into some of the assumptions being made and found (amongst other issues) coral reefs have been observed to survive from a few meters up to 160 m depth:
> "One of the main causes for recognition of the greater depth-vari ability of coral taxa has been the routine inclusion of deep-diving and ROV surveys in coral ecological studies over the past few decades, which has broken through the “shallow-water” bias of early surveys by adding frequent observations on deeper occurrences (although more are needed).
[...]
The amount of light received by corals varies spatially and tempora lly, and is influenced by cloud cover, turbidity, tidal changes, reef topography, and depth. The depth of light penetration varies with latitude and distance from the shore (Kleypas et al., 1999), with many coastal reefs receiving reduced light levels due to high turbidity. For example, in the most turbid regions of the Great Barrier Reef, corals are found only within the upper 3 to 4 m of the water column, while on the outer shelf, corals are found to depths up to 100 m (van Woesik and Done 1997, Hopley, 1994, Cooper et al., 2007). At some mid-ocean Pacific atolls, irradiance levels can be compatible with coral growth even at ~160 m depth (Montaggioni, 2005)."
https://www.sciencedirect.com/science/article/abs/pii/S027737911630
Sorry, those links got messed up:
https://pubs.geoscienceworld.org/gsa/books/monograph/2361/chapter/133567225/Holocene-Evolution-of-the-Western-Louisiana-Texas
https://www.sciencedirect.com/science/article/abs/pii/S0277379116301305
> Corals live in symbiosis with Zooxanthellae, photosynthetic organisms that need sunlight to survive, so a sudden deepening of more than 20 m would have killed off large amounts of Zooxanthellae and their coral hosts, leading to a coral mega-extinction, which is not in evidence.
Interesting idea, can you describe what evidence you looked for?