[Coral-List] Iron ooid fields of Mahengetang

[tomascik at novuscom.net]

Hi everyone,

“Geologists have a saying – rocks remember.”
-	Neil Armstrong

Going over some of my old underwater videos I came across a 1993 tape 
from Pulau Mahengetang located in the Sangihe Archipelago, Indonesia. 
During the expedition we thought that diving on the dome of an active 
submarine volcano (Banua Wuhu), about 600 m from Mahengetang, would be 
the highlight of our expedition. Well, we were wrong. During one of our 
exploratory dives we came across an amazing sight, a ‘desert’ in a 
middle of an extensive healthy fringing coral reef. We discovered an 
active iron ooid field that was venting gas and hydrothermal fluids. 
Here are two links to the video taken in 1993:

https://www.dropbox.com/s/99z00ft3mnf6tkq/Mahengetang%20Iron%20Ooid%20Filed.mp4?dl=0

https://1drv.ms/v/s!Aq1K6CQCBeATgtZvXhx5S2gskIPoMw?e=boesar

It was like finding a desert in a middle of a jungle. I still remember 
that before even thinking I proceeded to stick my hand into the sediment 
as deep as I could to see what was under there. Lucky for me the 
temperature below the surface layer was only 42C. We collected some of 
the venting gas in a small plastic water bottle to see what we may be 
dealing with. When brought to the surface the gas did not have any odor 
and it did not ignite when we tried to light it with a match. We assumed 
that it was probably CO2. The large iron ooid field was surrounded by a 
vibrant and healthy coral reef. The dominant corals that were found 
growing along the periphery of the ooid field were massive Porites spp. 
If anyone was wondering why I chose a quote about rocks and geologists 
the presence of massive Porites provides a clue, because those massive 
colonies are still waiting there to tell a story.

The main reason that I am posting this here is to encourage the coral 
reef research/conservation community to look at Pulau Mahengetang and 
its amazing reef as a natural laboratory to study ocean acidification. 
There are only a couple of other spots on the planet where this is 
possible. We all know that just like rocks corals ‘remember’ as well, 
and that we have learned a lot from the stories written in their 
skeletons. Those massive Porites colonies that surround the iron ooid 
field are still waiting there to tell their story. Mahengetang with 840 
inhabitants could be an ideal place for long term projects.

Anyone interested to learn more about the iron ooids fields of 
Mahengetang please visit:

https://www.researchgate.net/publication/249520305_Modern_iron_ooids_from_a_shallow-marine_volcanic_setting_Mahentang_Indonesia