How come you can see so well in the ocean? I understand that sand sinks to the bottom due to weight, but silt and other sediment that clouds lakes and rivers apparently has no effect in the ocean. Salt makes water denser which makes it more likely that things float and stay suspended in the water so that makes my failure to understand more discouraging.
I think I know why it stays on the bottom once it’s there…because the water pressure keeps it down.
Any visit to the ocean on either coast or the Gulf has given me spectacular views of clear blue or blue green water which I could see several feet into, but any lake was murky and cloudy. Lakes and rivers empty into the ocean…why is the ocean so clear?
In fresh water, silt remains suspended because of electrostatic repulsion between the bits of clay. The salt ions in the ocean bind to and neutralize the charges on the surface of silt particles which allows the suspended material to clump together (flocculate) and sink.
I suspect that ponds, etc. also have a higher loading of organic matter (humic & fulvic acids from rotting leaves, etc.) per unit volume as compared to the ocean which can pretty much dilute out anything you throw into it given enough time.
Also, not all ocean water is clear. Up here in good ole’ New England, the ocean water along the coastline is murky…presumably due to the high nutrient wash off from the land and the cold water temps. The waters of the Caribbean are crystal clear because very little organic matter is washing down from the islands.
The biggest reason the ocean is more clear than your local pond is that there’s a lot more water per volume crap dumped into it. A small pond can quite conceivably fill in during your lifetime; the ocean, well, …won’t. It also depends on the time of year - the late winter and spring near the mouth of the Fraser river will show a huge area around the Georgia strait totally brown from the river. The ocean also has tides that flush new water in and out. Differing salinities and temperatures, especially where there are a lot of rivers emptying or currents, can cause several layers of water that tend not to mix well. Lakes, ponds, and little streams are surrounded on all sides by land and have huge catchment areas many times there own size over which rain water flows, rinsing everything down into them. The open coast has much less run-off in comparison. It also depends on nutrients and plankton production. The sea doesn’t really go through turn-overs, so once stuff is down on the bottom, it usually stays there, unlike most lakes. When the ocean is clear, it’s usually safe to say that part of it is due to dilution.
Nope–pressure acts in all directions. In fact, since pressure increases with depth, it produces a larger force on the lower side of objects compare to the upper side, resulting in a net upward force. This is called buoyancy.
Another factor contributing to ocean clarity in the tropics is lack of mixing. The surface layer of the water is heated by the intense tropical sun and become significantly warmer than lower layers. (I believe the boundary is called the thermoclime.) Being warmer, it is also lighter and thus floats atop the colder water. The two layers don’t mix much, except during violent weather.(In northern latitudes, the temperature difference is much less, allowing the bottom waters to upwell, or the top layer, exposed to sub-zero air, gets colder and sinks.)
Organic material that would otherwise cloud the water sinks into this lower cold layer and becomes trapped. At least, thats what the marine biologists at the Shedd Aquarium told me when I worked there.
