Post #258952 by TikiJosh on Wed, Oct 4, 2006 1:28 PM

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 ]