# The ocean and sunlight **URL:** \ **Category:** Factual Questions\ **Created:** [October 6, 2001, 5:05am UTC](https://boards.straightdope.com/t/the-ocean-and-sunlight/85748 "2001-10-06T05:05:39Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![MagicalSilverKey](https://avatars.discourse-cdn.com/v4/letter/m/8797f3/32.png) [@MagicalSilverKey](https://boards.straightdope.com/u/MagicalSilverKey)\ **Post date:** [October 6, 2001, 5:05am UTC](https://boards.straightdope.com/t/the-ocean-and-sunlight/85748/1 "2001-10-06T05:05:39Z")
Imagine, if you will, that the entire oceans of the earth were as crystal clear as pure steam distlled water. If this was true, then how far down would sunlight be able to penentrate to the sea floor? In addition: How far down could a person be submerged in a submarine and still see the sunlight from above? ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [October 6, 2001, 11:55am UTC](https://boards.straightdope.com/t/the-ocean-and-sunlight/85748/2 "2001-10-06T11:55:38Z")
This is nothing but a WAG, but I’d say not terribly far. After all, a really cloudy day can be very dark, and that’s just water _vapor_ between you and the sun. My guess is the refractory capabilities of the water would scatter sunlight pretty effectively down to practically nothing right quick. ---
**Author:** ![Gaspode](https://avatars.discourse-cdn.com/v4/letter/g/aeb1de/32.png) [@Gaspode](https://boards.straightdope.com/u/Gaspode)\ **Post date:** [October 6, 2001, 12:21pm UTC](https://boards.straightdope.com/t/the-ocean-and-sunlight/85748/3 "2001-10-06T12:21:06Z")
Not very far. Visible light is absorbed very rapidly even by pure by salt water. About half of all light is absorbed in the first metre, about 3/4 is absorbed within 10 metres and less than 1% reaches 100 metres. Pure water sans salt will increase the penetration a little, but not greatly. Probably something like 75% being absorbed within 15 metres and still less than 1% reaching 100 metres. ---
**Author:** ![The\_Bad\_Astronomer](https://avatars.discourse-cdn.com/v4/letter/t/f05b48/32.png) [@The\_Bad\_Astronomer](https://boards.straightdope.com/u/The_Bad_Astronomer)\ **Post date:** [October 7, 2001, 4:52pm UTC](https://boards.straightdope.com/t/the-ocean-and-sunlight/85748/4 "2001-10-07T16:52:25Z")
> [@](#): > > \*Originally posted by Gaspode \* > \*\*Not very far. Visible light is absorbed very rapidly even by pure by salt water. \*\* Serious question: do you have a reference for that? One of the most common misconceptions in astronomy is that the sky is blue because oceans reflect blue light. When I answer it I talk about how red light is more strongly absorbed than blue in water, but I don’t have any numbers. If you have a cite that would help a lot! ---
**Author:** ![Gaspode](https://avatars.discourse-cdn.com/v4/letter/g/aeb1de/32.png) [@Gaspode](https://boards.straightdope.com/u/Gaspode)\ **Post date:** [October 7, 2001, 11:01pm UTC](https://boards.straightdope.com/t/the-ocean-and-sunlight/85748/5 "2001-10-07T23:01:48Z")
Well that was mostly from memory of Aquatic Biol classes about a decade ago, but a quick Google search turns up reams of sites dicussing light transmission in salt water, like [Seawater Absorbs radiation (attenuation) Transmits visible part of spectrum only -ca. 60% absorbed in first meter –80% by 10 m depth -only 1% available light left at 150 m -at about 250 m depth, intensity of illumination the same looking up or down Different wavelengths behave differently -long wavelengths (“red” end) preferentially absorbed -shorter wavelengths (“blue-green”) transmitted deeper](http://www.essc.psu.edu/~arthur/HeatSoundLightSeawat.txt) ---
**Author:** ![Bob\_Scene](https://avatars.discourse-cdn.com/v4/letter/b/e19adc/32.png) [@Bob\_Scene](https://boards.straightdope.com/u/Bob_Scene)\ **Post date:** [October 7, 2001, 11:27pm UTC](https://boards.straightdope.com/t/the-ocean-and-sunlight/85748/6 "2001-10-07T23:27:03Z")
> [@](#): > > \*Originally posted by KneadToKnow \* > \*\*This is nothing but a WAG, but I’d say not terribly far. After all, a really cloudy day can be very dark, and that’s just water _vapor_ between you and the sun. My guess is the refractory capabilities of the water would scatter sunlight pretty effectively down to practically nothing right quick. \*\* The scattering of light by clouds is caused by the presence of little droplets of liquid water (not vapor) with air in between them. The repeated refraction of rays of light at all the air/water interfaces is what causes scattering. Liquid that isn’t dispersed like that, and only has one interface with the air, won’t scatter light the same way. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [October 10, 2001, 12:16pm UTC](https://boards.straightdope.com/t/the-ocean-and-sunlight/85748/7 "2001-10-10T12:16:42Z")
I stand corrected.