Why?

[drewdude]

Ok, just came home from a trip (non-diving) from Monterey with the family. As I was checking out the water around the area, the question of water clarity kept popping up. Why is it that Monterey water is so much clearer than say my home waters (Humboldt County). I know the variables are many (run off, local currents, etc), but is there a single factor that makes the difference?

Inquiring minds want to know.

 

[dannobee]

While there are many variables in determining water clarity, the proximity of Monterey to a deep water canyon plays a major role in upwellings bringing clear ocean water. At least that is what I was told.


California Seafloor Mapping Program - USGS WCMG: Progress

 

[Eric Sedletzky]

What Danno said, It has a lot to do with the close proximity of the trench which comes right up to shore at Monastery.

For instance, Mendocino typically has better vis than Sonoma County. Why, I don't know. It might have something to do with out fall from SF bay?

But then you'd think that Monterey being south of SF and the prevailing north west winds would create a bigger low vis situation heading south. Take a look at everything from the gate down to Moss landing and you will see that the vis always sucks just north of Monterey Bay so maybe SF does have an effect and the trench with the upwellings holds it back? Who knows.

I do know one other thing, and that is that soil composition has a lot to do with it. For instance, in Sonoma County there are areas where a lot of clay are present in the cliffsides and the composition on the beaches which perpetually milks out the vis. Up in Mendocino County the structure is mostly volcanic so the water tends to be much cleaner. Maybe up in Humboldt the clay problem is present.

 

[kathydee]

The mountains in Humboldt county receive some of the highest rain fall in the state,thus experience a significant run off. I know the Mad, Klamath and many other rivers in Humboldt contribute sediment to the ocean, however, I am not exactly sure how this affects vis.

 

[fisheater]

Excellent question. Thanks for asking.

 

[drewdude]

Rivers do have an impact on ocean water clarity up here. The best time of year to dive is Sept/Oct, when the rivers are at their lowest output, and prior to the winter rains. I also hear that's when the plankton blooms are also at their lowest. I just find it interesting that Monterey is close to several rivers but does not seem to be affected by them.

 

[fofo]

Howdy!

Bottom composition also affects visibility. Around Monterey it's more sand and rocks, and the rocks are likely to be granite -- but there is some shale, of course. Further north there is more silt and mud (and mudstone).

 

[cmburch]

Upwelling brings rich nutrients for growth. Which can have a major effect on water clarity.

NOAA Ocean Explorer: Sanctuary Quest: Background

Sewage outfalls can also supply rich nutients for growth, but it would be very localized.

 

[Akimbo]

I agree with all of the above. You can see the difference day to day after a rain here in Mendocino. Big River turns brown for days after a heavy rain and you can see the stain out to the buoy off the headlands. Some of that topsoil settles on the shallow bottom and gets stirred up when big swells roll in, even if it doesn't rain. After a rare rain when I lived in San Diego, you could see relatively little impact on vis; even though the continental shelf is more than 100 miles wide.

The volume of rain water runoff concentrated by rivers is lower in Monterey. Carmel River is considered a creek up here. Other than the Columbia and a few rivers that feed the San Francisco Bay Delta, West Coast rivers are creeks to people in the east. Diving within 25 miles of the mouth of the Mississippi is pretty much an exercise in brail diving.