[Coral-List] Iron ooid fields of Mahengetang

[Risk, Michael]

   Hi Tom.

   That was truly a memorable trip. Personnel were yourself, fresh from
   your PhD at McGill, and those iconic papers on corals and nutrients.
   You were partway through that magnum opus on the coral reefs of
   Indonesia. Anmarie Mah, your wife, with her MSc on hurricanes with
   Colin Stearn. Jodie Smith, my wife, whose Nature paper on rapid climate
   change (1997: v. 386, p. 818) now seems eerily prescient as we watch
   the NAD weaken, and myself, as comedy relief. Would have been a shame
   had we all drowned.

   The overnight  trip  from Manado up into the blue (next stop,
   Philippines) was very hairy. Wind came up, ship began to roll. I fed
   Jodie enough Gravol to subdue Bigfoot. Ship would roll, put the port
   rail underwater, then roll back, put the starboard rail under. I
   thought, we are about one degree away from turning turtle. I spent the
   night wedged in the doorway of our "stateroom" with my BC on, Jodie's
   over my arm, ready to grab her and go over the side.

   We got there, and the "captain" (a local doctor) said "Fast trip! I
   just bought this boat from another guy. He didn't know anything-put too
   much ballast in! I took it all out. Fast trip!"

   That's nothing: same guy ran us onto a reef on the way back. We spent a
   day trying to get off, dumping all the freshwater, guys swimming around
   trying to pry the boat off with planks...then because we were a day
   late he tried to charge us a day more. I remember Tom and I carefully
   explaining to him that he could either fuggedabudit or feed the fishes.

   But then there was all this marvellous science. Few have had the
   opportunity to dive on an underwater vent, where excess CO2 was driving
   bleaching. The kicker was the oolite field.

   I remember looking at the sediment, thinking "wtf?? That's iron oxide!"
   and explaining to Tom that yes, it was a bfd.

   Oolitic iron ores occur worldwide, and the ones in places like
   Pennsylvania fuelled much of the Industrial Revolution. Their origin
   was always a mystery. The hardrock geologists, some of whom had not had
   a new idea since Hutton, had a scheme whereby calcareous oolites
   (common in places like Grand Bahamas Banks, Persian Gulf) were laid
   down, and then magically all replaced by iron-bearing hydrothermal
   fluids coming from...somewhere. Thirty years ago, Mike Kimberly (then
   at UToronto) suggested that they had formed as original precipitates,
   iron ooids. The differences are huge, in terms of transport-obviously,
   the density of Fe oxides is much higher than that of aragonite.

   Well, the hardrockers would have none of this, and Kimberley's ideas
   languished.

   Turns out he was right all along: Heikoop et al., 1996: Geology v. 24;
   no. 8; p. 759-762.

   There are other connections between volcanism and corals in that
   entrancing country. I sampled corals at  Banda, near the site where Tom
   has documented rapid coral colonization of fresh lava (the key is-no
   people). I used to carry with me a ginormous power hacksaw blade, with
   which I would hand-saw out slabs of sampled corals to take back to the
   lab. (Worked surprisingly well.) Those corals carried within their
   skeletons a black Fe-rich band, exactly coincident with the nearby
   eruption. Those bands oxidised orange (limonite) within hours. The
   Banda Band is described in Heikoop et al PALAIOS, 1996, V. 11, p.
   286-292.

   In a third example, Heikoop et al 1997 ( Lethaia, Vol. 29, pp. 125-139)
   show effects of ash falls on benthic communities, especially reefs,
   with the strongest evidence coming from some spectacular outcrops near
   Manado.

   These papers are all in what would be called "geological" journals.
   Sadly, the coral reef biological community has largely forgotten that
   coral reefs are the conjunction of both disciplines.

   Mike

   "One of the penalties of an ecological education is that one lives
   alone in a world of wounds." Aldo Leopold
     __________________________________________________________________

   From: Coral-List <coral-list-bounces at coral.aoml.noaa.gov> on behalf of
   Tomas via Coral-List <coral-list at coral.aoml.noaa.gov>
   Sent: Sunday, March 21, 2021 6:51 PM
   To: coral-list at coral.aoml.noaa.gov <coral-list at coral.aoml.noaa.gov>
   Subject: [Coral-List] Iron ooid fields of Mahengetang

   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:
   [1]https://www.dropbox.com/s/99z00ft3mnf6tkq/Mahengetang%20Iron%20Ooid%
   20Filed.mp4?dl=0
   [2]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 42C. 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:
   [3]https://www.researchgate.net/publication/249520305_Modern_iron_ooids
   _from_a_shallow-marine_volcanic_setting_Mahentang_Indonesia
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References

   1. https://www.dropbox.com/s/99z00ft3mnf6tkq/Mahengetang%20Iron%20Ooid%20Filed.mp4?dl=0
   2. https://1drv.ms/v/s!Aq1K6CQCBeATgtZvXhx5S2gskIPoMw?e=boesar
   3. https://www.researchgate.net/publication/249520305_Modern_iron_ooids_from_a_shallow-marine_volcanic_setting_Mahentang_Indonesia
   4. https://coral.aoml.noaa.gov/mailman/listinfo/coral-list