400 ft down, great vis & light

[skeet]

Appreciate all the links m d 45. It was an interesting story on tv but it looks like we can get a lot more from these sites.

 

[DA Aquamaster]

I read that the theoretical visibility limit in distilled water was something like 242ft. If that's true, how do you get any natural light 50% beyond that?

I think 660 ft/200m is generally regarded as the normal limit of any significant natural light and is considered to be the lower limit of the epipelagic zone.

 

[teksimple]

I read that the theoretical visibility limit in distilled water was something like 242ft. If that's true, how do you get any natural light 50% beyond that?

-Rob

To answer your specific question, Rob...

Visibility of a water column is quantitatively measured by scientists using a Secchi disk. This measures the ability to discern an object, not the amount of light that actually can get through the column of water. Two different (but related) things.

A water column that is cloudy or "long" enough will diffuse light so that objects can not be discerned from the background light field, but light still penetrates much further than that.

 

[rab]

Visibility of a water column is quantitatively measured by scientists using a Secchi disk. This measures the ability to discern an object, not the amount of light that actually can get through the column of water. Two different (but related) things.

I'd found the references to Secchi disks while searching for the original source of the "fact" rather than a reference. What I'm wondering is whether the 242ft would be the depth of the Secchi disk? One site gave the formula of D x 2.7 for the limit of the euphotic zone where D is the depth measured with the Secchi disk method. In other words, does this imply light at a depth of 242x2.7=653ft?

-Rob

 

[DeepSeaDan]

...I was working offshore - 200 miles off Newfoundland in the Hibernia oilfield. When not in sat., we would often launch the bell to practice unconcious diver recoveries. One day we received permission to train at 200 fsw. I think that day I witnessed some of the best visibility imagineable. While hanging off a guide wire @ 200', I could clearly see every detail of the bottom of the semi-submersible driling rig above. Looking down was just as amazing, though natural bottom was 730 fsw, and I couldn't see that!

Other times, we'd hop in the bell for an observation dive, usually to assist the driller with a down-hole procedure; we would be his "eyes." It was not uncommon that we'd approach depths of 300 fsw before switching on the bell exterior lighting. I don't know why the water was so clear in that area, but it was certainly a thing to behold...

Regards,
D.S.D.

 

[jonnythan]

http://website.lineone.net/~britannic98/photogal/rr_bow4.jpg

Those guys must have some impressive breathing skills to be at 350 feet on single 80s.
What did I miss?

 

[jonnythan]

http://website.lineone.net/~britannic98/photogal/gm_lb_plaque.jpg

Look at that tank!! Anyone know how big that puppy is?

 

[Soggy]

http://website.lineone.net/~britannic98/photogal/gm_lb_plaque.jpg

Look at that tank!! Anyone know how big that puppy is?

It looks like a t-bottle. I think the 98 expedition was the one Chatterton was on, so you can fill in the blanks.

 

[novadiver]

aqua zepp, as in zeppelin

 

[eponym]

What I'm wondering is whether the 242ft would be the depth of the Secchi disk? One site gave the formula of D x 2.7 for the limit of the euphotic zone where D is the depth measured with the Secchi disk method. In other words, does this imply light at a depth of 242x2.7=653ft?-Rob

I think it might be the other way around. At Crater Lake, which has good clarity, they measure viz w/Secchi disks and their record is just over forty meters. This comes from a recent talk with Mark Buktenica, the park's biologist.

-Bryan