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Why is warm water clear & cold water ugly?
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el chupacabra
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Mar 26, 2006, 06:10 PM
 
So in the tropics, ocean water is often a beautiful shade of clear, with a hint of blue. But nowhere in the world where oceans are cold and tundra like, or even as warm as 60 degrees F are the oceans clear enough to see more than 6 inches deep. Why oh why is this the case? I tried asking google but he didnt know the answer.

The only thing I can think of at the moment is that cold waters can contain more dissolved O2 and CO2 allowing more algae to grow.
     
Binarymix
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Mar 26, 2006, 06:23 PM
 
nevermind, didn't read the post fully.
     
Albert Pujols
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Mar 26, 2006, 06:47 PM
 
I'm just making a guess but, the rough water in the colder areas causes increased turbidity. But in the warmer areas, especially in the atolls, the water is calmer so there isn't much sand or other particulates mixing with the water so the water is clearer.

I'm just making stuff up though.
     
Railroader
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Mar 26, 2006, 07:13 PM
 
I am going to guess that colder water supports more micro life than warmer water due to the increased O2 like you stated.
     
iLikebeer
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Mar 26, 2006, 07:58 PM
 
Originally Posted by Railroader
I am going to guess that colder water supports more micro life than warmer water due to the increased O2 like you stated.
I'd go the other way and say the warm water usually has all the aquatic life like coral reefs, seaweed, and bacteria that cleans the water. Where it's cold, not much filtering going on with life processes and it just gets dirtier and dirtier.
( Last edited by iLikebeer; Mar 26, 2006 at 08:10 PM. )
     
ShortcutToMoncton
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Mar 26, 2006, 08:29 PM
 
If you're talking about the clear, blue water as found in the American tropics – it's because the water is extremely unproductive.

greg
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drmbb2
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Mar 26, 2006, 08:33 PM
 
In terms of plankton, some of the most productive waters in the world are the cold waters of the North Atlantic (eg. the grand banks), the Bering Sea, and the Northeast Pacific. That's why so many whale species migrate to those waters to fatten up.

Check out some of the ocean plankton production charts at NOAA and NASA - the northern and southern oceans are far more productive then the tropics.
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Mar 26, 2006, 08:42 PM
 
Very informative and interesting. Makes perfect sense.

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Railroader
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Mar 26, 2006, 08:51 PM
 
Originally Posted by iLikebeer
I'd go the other way and say the warm water usually has all the aquatic life like coral reefs, seaweed, and bacteria that cleans the water. Where it's cold, not much filtering going on with life processes and it just gets dirtier and dirtier.
I think there's more life in colder water. When I think of warmer waters I think of barren sandy beaches. Colder waters usually have life throughout it.

Hmmm... actually, when I thought about it more, I am COMPLETELY wrong about the O2 thing. It's CO2

Does cold water hold more CO2 though than warmer water? Maybe more micro-plant life is supported in the colder water with more CO2 in suspension..
     
ShortcutToMoncton
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Mar 26, 2006, 09:19 PM
 
Just copied this from my Introductory Oceanography textbook I got last year. Darker blue is lower productivity (as defined by chlorophyll concentration). I know this is too big for the guidelines, but I'm gonna post this picture here because if it's much smaller you can't make out the text too well.

[removed oversize image: please crop/resize before reposting -- tooki]
Sigh...full-sized scan right here

As you'll notice, there are definite patterns, such as the five large gyres (most blue spots...they act sorta like giant whirlpools) and that coastal areas have most productivity. This is because marine animals need nutrients, which are relatively scarce in ocean water but are most abundant along coasts, because of runoff. (Hence, why no one goes out in the middle of the ocean to fish for the most part – it's a coastal industry, although there are exceptions). There are also some aspects such as upwelling, which occurs along Western coasts – that's why Western South America and Africa is so productive, since oceans "suck" water down on Eastern coasts (giving high-O2, low-nutrient water to lower regions) and "pulls" it back up on Western shores, delivering high-nutrient water that results in high productivity.

Anyways, I took an entire course on some of this stuff, so there's a lot more to it than that. But we'll see how that works.

greg
( Last edited by ShortcutToMoncton; Mar 27, 2006 at 07:27 PM. )
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drmbb2
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Mar 26, 2006, 09:30 PM
 
Trust NASA kids to have some of the best web stuff on this topic:

http://kids.earth.nasa.gov/seawifs/i...secolor_lg.gif

(phytoplankton, or primary, production, as measured by chlorophyll content - purple and blue are low phytoplankton productivity, red is highest).

also, from this site - http://www.gma.org/herring/biology/d...ing_oceans.asp

"A recreational SCUBA-diver may consider North Atlantic waters to be murky, but the murkiness goes hand-in-hand with the high productivity that sustains fish populations as well as the birds, marine mammals and humans dependent upon them. Nutrient rich water is the source of the soup of phytoplankton and zooplankton that, in some cases (e.g. herring), can directly sustain an entire fishery."

and

"The biological productivity found in a temperate coastal body of water like the Gulf of Maine could not be matched by a coral reef of equivalent size. Tropical waters are characterized by high light levels and nutrient-poor (crystal-clear) waters."

I did a lot more then one course in this stuff - all my MSc and PhD work was on hydrothermal vent tubeworms genetics, so I also had to do a lot of physical and biological oceanography (and spent a lot of time at sea).
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ShortcutToMoncton
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Mar 26, 2006, 09:32 PM
 
Originally Posted by Railroader
Does cold water hold more CO2 though than warmer water?
Cold water holds more dissolved gas than warm water, yeah.

greg

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Brass
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Mar 26, 2006, 09:40 PM
 
It's because you're wrong. (maybe)

The water where I live is very cold in Winter, but can be very clear. I was sitting in the boat while my friends were scuba diving a few years ago. The air temperature was only a bit above freezing (0°C), but I could see them very clearly on the bottom, 20 metres below.

Also, tropical water can sometimes be very unclear, especially when all the corals, animal, etc are breeding.

As someone else suggested, it is usually turbulence and/or lots of life that make the water unclear.
     
ShortcutToMoncton
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Mar 26, 2006, 10:29 PM
 
Ocean colour is influenced by 1) amount of turbidity (suspended material) from runoff, and 2) amount of photosynthetic pigment (ie. microorganisms, which increase with biological production), both of which increase the degree of light absorption and therefore decrease the distance to which visible light can penetrate the ocean.

So, coastal areas and upwellings are productive and green-yellow because they contain large amounts of yellow-gree algae and suspended particles. These materials disperse solar radiation so that the wavelength for green and yellow are dispersed most.

Water in open ocean lacks productivity and turbidity, so it's usually a clear indigo-blue. Water molecules disperse most solar radiation at the wavelength for blue light.

For example, at 10m under water, only ~16% of solar energy falling on the surface remains, mostly concentrated on the indigo-blue-green and some yellow spectrum. Thus, I don't think you can have the colour "red" below 10-11 meters into the ocean – all that wavelength has been absorbed already.

greg

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( Last edited by ShortcutToMoncton; Mar 27, 2006 at 07:29 PM. )
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ghporter
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Mar 27, 2006, 10:29 AM
 
Cold water can also dissolve more air than warm water, so it looks less clear.

I've seen extrememly clear and VERY COLD water in the Great Lakes, particularly Lake Superior. The reason is a combination of less microbial content and depth, which reduces turbulence throughout the water column. It's DARK blue and almost eerie.

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SirCastor
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Mar 27, 2006, 11:35 AM
 
Up in Oregon, there's a national park called Opal Creek. The water there is the clearest I can recall, and it's typically 40 F

Just an argument for the other side...
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villalobos
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Mar 27, 2006, 08:16 PM
 
Originally Posted by SirCastor
Up in Oregon, there's a national park called Opal Creek. The water there is the clearest I can recall, and it's typically 40 F

Just an argument for the other side...
I was going to mention Lake Superior as GHPorter did, or most moutain 'lakes' or pounds which have very clear water (lakes in Rocky Mountain NP). The water is there too cold to allow life.

Here is the chart to calculate the oxygen concentration in water as a function of the temperature.




Coming from this very well done site.
     
awaspaas
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Mar 27, 2006, 09:18 PM
 
Originally Posted by Railroader
Does cold water hold more CO2 though than warmer water? Maybe more micro-plant life is supported in the colder water with more CO2 in suspension..
Tada:

     
iLikebeer
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Mar 27, 2006, 10:40 PM
 
Originally Posted by iLikebeer
I'd go the other way and say the warm water usually has all the aquatic life like coral reefs, seaweed, and bacteria that cleans the water. Where it's cold, not much filtering going on with life processes and it just gets dirtier and dirtier.
lol, so i was completely wrong. At least I learned something new today.
     
ShortcutToMoncton
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Mar 27, 2006, 11:08 PM
 
Originally Posted by villalobos
I was going to mention Lake Superior as GHPorter did, or most moutain 'lakes' or pounds which have very clear water (lakes in Rocky Mountain NP). The water is there too cold to allow life.
No no no no no! People seemed to be getting the wrong idea about this.

Temperature does NOT have a function on the "clearness" of water. The two factors that I mentioned above determine how water looks.

There is no "water that is too cold to allow life" – life exists at all water temperatures, since (if you think about it) water only exists down to 0 degrees Celsius, or slightly below that depending on solute concentration. 0 C is certainly not too cold for a countless number or organisms. The reason some high-mountain lakes may be very "blue" or clear is because they have extremely low productivity, much like the open ocean. These lakes have few nutrients because of a variety of factors, such as lack of runoff from surrounding rocky areas (eg. little organic material flowing in). Conversely, you may notice that some Rocky Mountain lakes (such as Lake Louise here in Alberta) are bright blue-green, and not very clear at all! This isn't because of how cold they are – it's often because of high ion concentration runoff from surrounding rocky areas, which in turn reflect light at certain wavelengths. These lakes may also have low nutrient (and thus organism) content, but they may not be clear because of this other suspended material.

Originally Posted by ghporter
Cold water can also dissolve more air than warm water, so it looks less clear.

I've seen extrememly clear and VERY COLD water in the Great Lakes, particularly Lake Superior. The reason is a combination of less microbial content and depth, which reduces turbulence throughout the water column. It's DARK blue and almost eerie.
Again, less microbial content means light is reflected only (or mostly) at the wavelength of the water molecule, which is that of the colour blue. Higher turbidity and photosynthetic pigment reflect more of the visible spectrum, and thus the water can be murky or look like a different colour.

I'll quote my own post again, just for posterity:

Originally Posted by ShortcutToMoncton
Ocean colour is influenced by 1) amount of turbidity (suspended material) from runoff, and 2) amount of photosynthetic pigment (ie. microorganisms, which increase with biological production), both of which increase the degree of light absorption and therefore decrease the distance to which visible light can penetrate the ocean.

So, coastal areas and upwellings are productive and green-yellow because they contain large amounts of yellow-gree algae and suspended particles. These materials disperse solar radiation so that the wavelength for green and yellow are dispersed most.

Water in open ocean lacks productivity and turbidity, so it's usually a clear indigo-blue. Water molecules disperse most solar radiation at the wavelength for blue light.

For example, at 10m under water, only ~16% of solar energy falling on the surface remains, mostly concentrated on the indigo-blue-green and some yellow spectrum. Thus, I don't think you can have the colour "red" below 10-11 meters into the ocean – all that wavelength has been absorbed already.
To sum up: the original question is flawed (not to mention, inaccurate – since when can you not see more than 6 inches into cold water?!?!). While temperature does have a rather small effect on the solubility of gases, it's relatively low over the temperature range of the ocean. Rather, turbidity and photosynthetic pigment cause changes in water clarity. The reason his "tropical water" is such a beautiful shade of clear blue is a function of the low productivity in water of that region because of oceanic (and terrestrial) processes.

greg
( Last edited by ShortcutToMoncton; Mar 28, 2006 at 04:40 AM. )
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