Ocean salinity

[maddog]

I was watching TV the other day, and saw part of a program on PBS which I suspect was about global warming and oceans. The part I saw had something to do with the ocean currents, and particularly the importance of the Atlantic circulation pattern, that brings warm tropical water up the west coast of Britain and Ireland. Now, they were saying that they were measuring something in the northern sea, near Greenland. Salt water dives down there, and then is forced up and out into the current pattern. It sort of "drives the engine" of worldwide ocean circulation and currents. But over the last 30-40 years, the water in the "diving down" northern sea trough is getting increasingly more fresh, and less salt-sea water. Because fresh water is "lighter" and salt water is "heavier," the fresh water just rides on the top. No salt water is being "forced down" in the northern sea area, so the danger is that the whole ocean circulation "engine" will stop. The question they were going on to (before I conked out) was, "where is all the fresh water coming from." If I were a betting person, I would have bet that the answer was "from melting arctic ice." Does anybody know more about this problem? Is melting polar ice the correct answer? What would be the results if the ocean currents stopped? Do you think that's a likely consequence of whatever's going on?

I know there's already a kind of global warming thread going, but (1) this program (which I admittedly missed most of ) was focused on the oceans and the fresh water/salt water/current flow problem, and (2) I promised liv I'd start a new thread in honor of the new hippo smilie I'd asked for! Can anybody fill in the blanks on this ocean current thing? It sounds scary and important!
#311

[ceptimus]

I know a bit about it.

The Gulf Stream is responsible for transporting heat from the tropics to Northern Europe. Britain is at roughly the same latitude as Newfoundland, but we have much milder winters here in Britain. The Gulf stream is what keeps us relatively warm.

On the surface of the Atlantic, the Gulf Stream flows from the Caribbean towards Britain. The water then cools, and contracts slightly as it does so. The cooler denser water sinks down, and lower in the Atlantic it is flowing in the opposite direction.

So there is a circulation, driven by heat, and it carries heat from warm equatorial regions to cooler northern ones.

So far so good, but the temperature of water is not the only thing that affects its density. Salt water is denser than fresh water. The concern is that warmer weather is causing a huge amount of fresh water, trapped in the form of snow and ice to melt. The ice sheet covering Greenland is significantly thinner than it was a few years ago, and this means that billions of tons of fresh water are being dumped into the northern Atlantic each year, as the ice melts.

The concern is that the reduced salinity at northern latitudes will counteract the increasing density due to the water cooling, and this could cause the Gulf stream to switch off. There is evidence in the geological record that this has happened many times previously, and that when the Gulf stream does switch off, it happens in a geological 'instant' maybe just five years or so.

If and when the Gulf stream does switch off, it will plunge Britain and other parts of Northern Europe into a mini Ice Age, so paradoxically, global warming may make us colder.

[beatsme]

Last year I read several articles on this subject. Though I can't vouch for the sources, they are the following:

"Climate Collapse" by David Stipp in the January 26, 2004 issue of Fortune, (I have no link);

"How Global Warming May Cause the Next Ice Age..." by Thom Hartmann published on Friday, January 30, 2004 by Common Dreams.org: http://www.commondreams.org/views04/0130-11.htm,
and

"The Pentagon Sounds the Alarm on Global Warming; Why Isn't President Bush Listening?" by Arianna Huffington published on Wednesday, February 25, 2004, also by Common Dreams.org:http://www.commondreams.org/views04/0225-13.htm