Water Clarity

[Bill Gwynn]

I was wondering why the water is so much clearer now than it is in the summer. I'm sure it's a combination of things. I'm sure that with the water so cold there isn't that much food (plankton etc.) in the water, also there is very little boat traffic, therefore no stirring up of things and less pollution. I was curious if any one could tell me what the biggest factor is regarding water clarity. Is it the lack of marine life in this cold water, pollution from boats, or something else I didn't think of?

Bill

P&H Capella...All White

[Guest guest]

I'm So not an expert here, and hope someone will chime in, but I've always thought the main issue was the water temperature -- that since the ocean is so big the temperature is relatively stable but in the summer the rivers and all are warmer than the sea and this warmer water flowing into the bottom of a column of ocean then rises up toward the cold carrying plankton and other miniature stuff that refracts the light. Is this right?

Besides lack of boaters, the storm activity before you were paddling is also key I imagine for turbidity and a lack of rain would have less eroded stuff, too.

--b

[Don]

As a diver, I usually have much better visibility in the spring than later in the summer. This is primarily a matter of reduced plankton growth.

Storms can change visibility rather quickly, though.

The interesting thing that I haven't ever really had explained well to me, though is the difference in visibility between the water up here, vs. the water in the Caribbean or Pacific. Warm water divers often have 100-200' visibility, while we consider ourselves lucky up here to get 50', and that's only in the winter or spring- more likely we'll have 10-20' during the summer.

The difference does seem to do with the oxygen levels in cold vs. warm water, upwellings, etc. - but it does seem counterintuitive that our waters are much more productive biomass-wise. In the Caribbean it's not unusual to be surrounded by fish, whereas up here you're much more likely to just see an occasional fish.

I guess it's like Dark Matter - most of the stuff is so small you just don't notice it.

Don

[Shane]

I seem to recall that cold water is more dense than that of warm water and as a result holds more "stuff" such as nutrients, algaes, etc... If so, that would likely be a culprit of the visibility effect.

_Shane

"Would a knife help protect you against a ‘curious’ shark? I don’t know but I would like the option." - Trevor Gardner

[Guest guest]

The following is a good description of the differences in water clarity cold vs warmer tropic seas. Basically nutrients settle in tropic waters at the colder deeper levels. Light travels a lot further (more clarity) before reflecting off these particles. (read below for more).

Deb

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This is because in tropical areas the nutrients settle beneath thermoclines and the temperature related density differences within the thermocline prevent the nutrients from returning to surface waters. This means that there are little or no plankton growing in these regions due to the lack of nutrients in the water. It is plankton that cause cloudiness in ocean water. Also turbidity (water clarity) is affected by wave action in shallow water. Since most of those pictures are taken of rocky or sandy bayline seashores, there just isn't enough wave action or the sand is too "clean" to produce the cloudy effects. Wave bombardment in temperate regions will often froth the water and nutrients in to a tannish brown surf but the clarity will reappear several hundred yards out from the shore. In colder waters, the oceans provide excellent visibility for most of the year, but in late spring and summer, the algae and plankton "blooms" cause some turbidity.

Light consists of several different wavelengths that we see as color when they are separated. The infrared and red side of the spectrum is very short lived in water as depth increases. Most of this light is absorbed as heat in the oceans as well. As we approach the greener middle portion of the spectrum, the light reaches deep enough to be reflected back from particles in the ocean. In temperate regions the particulate matter is denser in the water and so some reddish light and some greenish light is reflected back to our eyes along with blue/violet. This can give the ocean a greenish brown hue that masks the blue color. IN tropical waters where the nutrient and plankton particulate matter are sparse, light must travel deeper to reach enough particles to be reflected back for us to view it. The only light that has the wavelength necessary to travel deep enough to reach a reflective point and thus be visible to us are the blue/violet/ultraviolet portions of the spectrum. This is why in tropical waters the deep blue sea is just that. I hope this mini dissertation has been as fun for you as it was for me.

[Brian Nystrom]

It may also be the nature of the bottom. The Caribbean is predominantly sand and coral reefs. Despite the abundance of life on the reefs, they are a relatively low nutrient environment. You learn this when you try to raise salt water tropical fish in aquaria. The biggest problem is keeping the levels of nutrients (Nitrates, phosphates, organics) as low as on the reef. Higher nutient levels produce algae blooms, as we see here in the summer.

Those who paddled Walden Pond in the spring are treated to crystal clear water, but once it reaches a certain temperature, the algae explodes and visibility goes from 30'+ to 10' or less in a matter of a week.