Before and After
Mound Corals at Shark’s Cove, Oahu, Hawaii. The corals appear to be oxidizing and dissolving from accelerated corrosion. Photos courtesy Terry Lilley & Pamela Whitman.
———- Forwarded message ———-
From: ChemE Stewart<cheme911@gmail.com>
Date: Tue, Apr 12, 2016 at 2:00 PM
Subject: Mound corals before and after at Sharks Cove
To: “underwater2web .” <underwater2web@gmail.com>
Cc: a producer, a >, an environmental activist, an environmental activist, a radio talk show host, a navy biologist, a government scientist
Terry,
That reef (what remains) looks awfully reddish/orange/brown…
Corrosion Damage:
“This type of damage typically produces oxide(s) or salt(s) of the original metal, and results in a distinctive orange colouration. “
Accelerated corrosion could cause the calcium to lose electrons, which then leaves the Ca2+ to be attacked by Cl- and OH- ions in the seawater, producing CaCl2 and/or Ca(OH)2
CaCl2 that precipitates out and later dissolves in seawater can be orange, especially when it is oxidizing:
 |
orange |
calcium salts calcium chloride, CaCl2 |
628 |
Iron oxides are also orange/red -they could leach into the area from ships, steel structures, underwater metal gear, volcanic rock, etc.
Colors of Corrosion
The first testing I would do is check the reef for corrosion by-products, ie. metal salts and metal oxides (most of which eventually dissolve in seawater)
If it is corrosion, then it is accelerated by the following, roughly in this order of sensitivity:
- EMF (electromotive force) due to
- stray electrical current corrosion (antennas, increased voltage in atmosphere over reef, improper grounding, electrical currents in seawater) near reef
- galvanic corrosion (steel/aluminum from boats/structures or underwater gear in seawater near reef)
- Drop in pH
- Increase in temperature
- Drop in Salinity
- Increase in Dissolved Oxygen
- Drop in Dissolved Solids
My experience in industry tells me that it takes quite an increase in temperature or drop in pH to accelerate steel corrosion significantly, not sure about calcium/magnesium in a reef structure
Here is an article that sounds/looks like accelerated/galvanic corrosion of a reef to me from iron/steel in a shipwreck’s structure coupling with the minerals in the reef.
This looks like galvanic corrosion between the steel and calcium/magnesium in the coral reef. The reef died around the shipwreck.
Terry, if it is corrosion, it might even be accelerated by your steel SCUBA tank and zodiac steel propeller(galvanic corrosion) while hovering near the reef…stop diving so much…
OMG that’s not funny!
Aloha,
Stewart
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