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[Scott C. Mitchell]

The January 2015 article of Scientific American has an article titled "In Search of Sunken Treasure".  It features (paraphrasing from the Summary) new technologies for underwater archaeological searches and excavations, including *rebreathers* that allow divers to stay at 165 foot depth for up to 90 minutes, instead of only 8 minutes with regular scuba gear; a *metallic Exosuit* that let divers work underwater at surface air pressure; and the Sirius dive-robot which was designed to survey unusual structures, with high-resolution cameras.  The *rebreather* sounds interesting; those standard scuba dive tables are unforgiving for bottom time.

Scott
#3292

[John B. Shattuck]

Rebreathers offer many advantages for diving beyond recreational depth; the most significant of which is probably a constant partial pressure for Oxygen (O2 percentage in normal breathing air starts to get toxic beyond certain depths);  but the requirements to decompress remain.  And in that regard, so do the dangers of decompression sickness.  Given the remoteness of Niku, you would either have to avoid decompression obligations, or bring a recompression chamber (and doctor) along for safety. 

The 600 foot depth of the Richie Anomaly, combined with the remoteness of the dive site and apparently rugged terrain, make for an extremely hazardous undertaking  for divers--much better and safer options with manned/unmanned submersibles.  Where I think divers could be helpful is the first 140-200 feet of depth along the "Bevington object-wire rope video-Richie Anomaly line" to look for debris.  Again, depth and time conspire to incur decompression obligations even at relatively shallow depths.  165 feet for 20 minutes incurs 30 minutes of decompression for open circuit (normal SCUBA) or 21 minutes for a closed circuit (rebreather).  Up to 130 feet of depth can be explored without decompression obligations but bottom time is very limited (as Scott pointed out).  Of course, who knows what lies waiting for discovery in the first 100 feet, where bottom time is greater and risks far less numerous.

[Greg Daspit]

That area at the top of the first
cliff just above the Debris Field seems to be a promising area to search. Not sure of the depth or if scuba search is feasible there?
Edit:
Attachment shows 70' but I believe the cliff height varies.

[John B. Shattuck]

70 feet is not technically challenging at all and is actually within recreational diving limits.  A technical diver properly equipped could spend significantly longer time.  I've spent up to two hours on dives at that depth.  The 250 foot level is reachable for those properly trained/equipped for it but we are deeply (pun intended) into the technical diving realm here.

I'm not advocating any dives at all without some seriously significant safety overhead; namely a recompression chamber and a Doctor trained in diving emergencies.  Too much can happen, and given the remoteness, a problem elsewhere could be a crisis here.

The logistics of supporting a team of technical divers may be a reach too far as well.  Air compressors and O2 bottles to refill tanks; even rebreathers require O2 and bail-out tanks, as well as back-up and contingency gear.  The complexity curve is probably asymptotic... pretty easy for the first 130 feet or so, but starts getting more and more dificult to support for every 33 feet beyond that (33 feet being another atmosphere worth of depth).  All said, I imagine a search in the first 125 feet; or restricted to the top of the first cliff (somewhere around 70 feet) could be supportable and potentially worth doing.  Ric and company will have to decide if the overhead is worth the potential gain.

JB