What determines the color of tropical oceans?

I have often wondered why the water in tropical and sub-tropical areas is so radically different from the color of the ocean in other areas, (like the california coast, for example). Even the mediteranean sea has that incredible, light blue or light green color. I want to say it's the coral, but you see this color in places that don't even have coral. Can anyone answer this?

Good question. I'd like to know the answer, too.

It gets it's color from what is beneath it.

I think this link will answer your question.

http://science.hq.nasa.gov/oceans/living/color.html

Greg
http://www.flatearthtrading.com

I actually read that page before, but I can't seem to understand it. Basically, they are saying it is the phytoplankton that determines it. Why would there be a dramatic difference in phytoplankton in a tropical ocean versus oceans the rest of the world over? Take california, for instance. The ocean color goes from grey to dark green-blue. It always looks exactly the same as any ocean you would find in England, for example.

Now look at this:
http://community.middlebury.edu/~scs/corbis_big/10917280.jpg

Is it the phytoplankton only, or the color of that sand underneath? I have seen rivers in Hawaii, or lagoons that should not have any plankton, that also have that color. Particularly, last time I was on the west shore of Oahu, we passed over a bridge where a river was coming out, with this exact color.

I looked for a picture I once saw of Chinese Junks floating in the China sea. The entire harbor looked like green anti-freeze. Is that all plankton?

I wish I knew for sure.

Look at this one: This is the Maldives, indian ocean. Look at the incredible color inside the reef, in the small harbor at the bottom of the picture.
http://en.wikipedia.org/wiki/Image:Male-total.jpg

In this case I can definately say it's the coral, but you can also see this color when there is no coral whatsoever.

This is a beach in Greece, not even close to being tropical, but look at the delicious color of the water!

http://en.wikipedia.org/wiki/Image:Porto_katsiki_beach.jpg

The answer to the question about why California has more plankton, etc. than a tropical place like Hawaii relates to the ocean currents in those areas. Tropical regions, such as Hawaii, generally have very nutrient poor water. The corals are experts at nutrient recycling which is why they can live in relatively clear, clean water, and probably also part of the reason why they grow so slowly. The coral polyp produces waste just like any animal, and the symbiotic algae use that waste for photosynthesis. Because there's not a lot of nutrients floating around, you don't get dense areas of seaweed/kelp/algae/phytoplankton, at least not like the kelp forests of California.
The reason California is so special is because our main current is the California current, which comes from the north and heads south. A current moving from north to south produces Ekman transport to the west. I'm sure there's tons of info on Ekman transport online if you want to read more about it, but the gist is that as surface water moves, it can "drag" some of the water under it, but it doesn't drag in a perfectly straight line. The lower layers tend to almost spiral, until you get some water moving perpendicular to the original direction of water flow. In other words, a current moving to the south can cause lower layers of water to move to the west. Generally, as water moves by Ekman transport, the surrounding ocean fills it in. In California, however, there's just a lot of land to the east, so deep water fills in the gap left by Ekman transport. This process, called upwelling, brings nutrient rich water from very deep in the ocean which can feed phytoplankton blooms and kelp forests.
And that's why the ocean is greenish in California and nice azure blue in Hawaii.

On several occasions, at several different oceans, various people have told me the color is from the suns reflection relevant to hemisphere, location, refraction, and depth.

In Tangier Morocco, if you stand on the top level of the Kasbah (no, I'm not making this up), you'll see three different large bodies of water directly next to each other (Atlantic, Mediterranean, and The Strait of Gibraltar). They're each different colors. I was told that the color differentiation was due to depth differences.

It is really a plot by Crayola to sell more crayons. The more colors in oceans the more boxes they can sell. I remember a few years back they were selling small boxes of colors specific to a theme. One box had 16 colors of blue for water. 16 different colors.

Water color is like the color of the sky and there are as many reasons for the differences in each. The biggest three reasons for any difference in water color in large bodies are Temperature, Depth, and Content (mineral or other).

On 2006-10-03 13:13, Coco Loco wrote:
On several occasions, at several different oceans, various people have told me the color is from the suns reflection relevant to hemisphere, location, refraction, and depth.

In Tangier Morocco, if you stand on the top level of the Kasbah (no, I'm not making this up), you'll see three different large bodies of water directly next to each other (Atlantic, Mediterranean, and The Strait of Gibraltar). They're each different colors. I was told that the color differentiation was due to depth differences.

Yes. The changes in blue color from one place to another have a lot to do with the way the sunlight hits the water and is refracted and reflected, in relation to depth. Since water molecules absorb light from the red end of the visible spectrum first, most of the light that gets reflected is blue. In shallower water, it's possible to have some light penetrate to the bottom, and get reflected back out, so it's bright, light blue, almost like a swimming pool. Deeper areas won't reflect hardly any red light, so they tend to look very dark blue, almost black. Depth will definitely have an impact on what you see.
Regarding your Kasbah story, the color differences you observe is related to what's called a "mixing zone" or a "boundary zone". What you are observing are three chemically and biologically distinct bodies of water. Each has it's own unique concentration of phytoplankton, trace minerals, etc. While depth can have an effect (see above), it's not likely the only reason for the observation you're reporting.

On 2006-10-03 14:00, Chip and Andy wrote:

Water color is like the color of the sky and there are as many reasons for the differences in each. The biggest three reasons for any difference in water color in large bodies are Temperature, Depth, and Content (mineral or other).

And yes, absolutely right.
So, what about the beaches that are brown? That's just from the sand, right? :wink:

[ Edited by: TikiJosh 2006-10-04 14:57 ]

A lot of good ideas here, but still I am a bit confused.

Take Newport Harbor (in Socal). There are places where the water is obviously shallow, and you can more or less see the bottom, but it does not have that obvious light green anti-freeze color that a tropical lagoon does. It makes me think that depth has nothing to do with it.

Then there is the color of the sand. In the example I posted above on a meditaranean beach in Greece, the sand is not radically different from the sand on any other beach (White sand beaches excluded) yet, the water is a bright, pale blue color.

I tend to believe the poster who talked about currents might be more

All these years I thought it was the earths position relative to the sun causing the different colors in the water. Silly me! Here are some photos from my collection of water colors. I often use the ocean colors for inspiration in my beaded work.

Here is water off the coast of Guam, the very deep Marianas Trench:
With the kids out of the way:

Guam beach:

Hawaii, Bellows Beach:

Judy at Emerald Bay, Lake Tahoe:

"The Beach" Pi Pi Islands, Thailand:

Some where else in the Pi Pi Islands, we went snorkeling and were bitten all over by something microscopic. Maybe that is why the water is so pretty: carnivorous plankton! The guides tried to convince us it was our sunscreen reacting to the salt water. RIGHT...

Great Barrier Reef, Australia:

Kuta Beach, Bali:

Hickam Harbor, Oahu, Hawaii:

And the view outside my house a few minutes ago:

you really don't want to know why the water in So. Cal. is brown. espicially the Newport/ Huntington area.
after hearing why, and going to Hawaii, I never go in the water here any more.

Jeff(bigtikidude)

On 2006-10-03 15:52, lucas vigor wrote:
A lot of good ideas here, but still I am a bit confused.

Take Newport Harbor (in Socal). There are places where the water is obviously shallow, and you can more or less see the bottom, but it does not have that obvious light green anti-freeze color that a tropical lagoon does. It makes me think that depth has nothing to do with it.

I guess my first post was a bit short. Let me see if I can help with some extra info.
Part of the problem is that one single factor does not determine the color of the water, just like one single factor does not determine the color of the sky. Allow me to digress by way of an example. In So Cal, we have so much smog, that on most days, if you look towards the inland mountains, you either a. can't see them through the haze, or b. the sky looks brown. Now during a sunset, the sky can be pink and purple off to the west. It goes from brown to pink simply by changing the angle at which the sunlight hits the smog. If I remember correctly, not too many other places in the world have the same kind of smog cover that we have, but they also don't have pink sunsets. If you board an airplane, and fly in any direction, the sky will be blue when you get above most of the lingering smog. Changing your location, the angle of incidence of sunlight, etc, can affect the way the sky looks.

The same kind of causative agents can affect the way the water looks.

You have to consider not only the water currents, but the direction in which they move and any additonal impact that may have (i.e. the upwelling that occurs in our oceans off California). One of the by-products of the upwelling created by the action of our offshore currents is the movement of a lot of nutrients from deep water up into the shallower water where those nutrients can be used for photosynthesis. This results in a high level of primary productivity in open water, which is not typical in tropical areas. This is the biggest reason why the ocean off California is green, and blue in the tropics. It's not that there's no primary productivity (i.e. phytoplankton), it's just that it's not in as high abundance.
Here's a link to a picture from the Nasa website. You can see the plume of greenish water that comes from bays, and rivers as they empty into the ocean. There's one that's almost right in the center of the picture. That's not because the water is polluted, it's because all the stuff coming into the ocean-- sediments, dead leaves, dead bugs, etc will eventually be converted to nutrients and food for something. What you see is basically a plankton bloom in those areas. It's a pretty big picture, so be patient:
http://veimages.gsfc.nasa.gov/6469/California.A2004304.1825.250m.jpg

In addition to phytoplankton concentrations, the concentration of other dissolved compounds can also affect water color (as Chip and Andy said). If you ever go snorkeling locally, you'll notice that there are tons more suspended particles in the water as a result of upwelling, which I mentioned above. If you ever go Scuba Diving and try to take underwater pictures with a flash, the effect called backscatter is a result of illuminating all those suspended particles with the camera's flash.
These suspended particles can either a. absorb light directly, or b. act like fertilizer and cause more plankton to grow. The more plankton there is, the more green the water will look.

Additonally, depth will definitely affect the way the water looks. There's just not a single explanation for all the nuances of the color of the ocean. Here's an example of the effect depth can have on water color:
Have a look again at this pic that WenikiTiki posted:

You can see how the water is greenish over the reef flat. If you remember your visible light spectrum, violet and blue at one end and red at the other, green is almost right in the middle. If you add a little more red light to something blue, it's gonna look greenish. That's what happens where it's shallow. All the red light doesn't get absorbed, and what you see is a combo of the blue plus the remaining reds. When you go out past the reef crest, you can see where it drops off, and the water turns dark blue. So depth definitely has something to do with it.

Rocks and other stuff near the surface will also affect water color:
Look again at WenikiTiki's picture of the GBR:

You can see part of the reef structure coming up from the bottom, which is creating the dark mottling effect in what would otherwise be very clear blue water. Sometimes, if the rocks are not very near the surface, it can just make the water appear a little on the green side, rather than dark like in the photo.

To sum up, there are several reasons that the water in California, like in Newport Bay isn't going to look blue like a reef flat.
The increased primary productivity as a result of upwelling is your big reason. In even shallow water, there's enough floating around to affect the water color.
Numerous other factors will also affect the water color in any given place. The local cloud cover might even have an effect. What you're ultimately talking about are several things that all intersect in a very unique way at one particular beach or region of the ocean. Primary productivity, suspended sediments, physical structures like rocks, depth of water-- all these things are going to affect what you see, and because these processes are all connected it's very hard to say how much effect each thing has on the color of the water.

[ Edited by: TikiJosh 2006-10-04 13:34 ]

[ Edited by: TikiJosh 2006-10-04 13:40 ]

[ Edited by: TikiJosh 2006-10-04 15:35 ]

That was an excellent analysis, and I think it explains things very well! Thank you for taking the time to solve this mystery for me!

No problem. I must be going through teaching withdrawals. :wink:

"They say the smog is the reason we have such beautiful sunsets."

/Get Shorty