On Oct 29, 8:46 am, James Annan <[EMAIL PROTECTED]> wrote: > Michael Tobis wrote: > > I'm not sure why this should be directed at me in particular, though I > > don't know if we have any bona fide oceanographers here. I'll give it > > a try. > > > There are fundamentally very different mechanisms moving water > > horizontally and moving it vertically in the ocean. (Actually, the > > same can be said for any stratified fluid.) > > [...] > > > > > > > > > Now this wind-driven pattern, it turns out, does not penetrate to the > > depths of the ocean (poetically known as the "abyss"). So what happens > > to the abyssal waters? Do they just sit there entirely stagnant, > > mixing with the upper ocean very slowly through diffusion? No, there > > is a process which is much slower than the wind-driven circulation and > > much faster than diffusion which forms the connection between the > > surface waters and the abyss. This is the thermohaline circulation, or > > THC to its friends. > > > It is driven by ice phase changes. When ice forms, of course the > > temperature is near freezing. Because pure water freezes better than > > salt water does, removing heat from seawater at the freezing point > > makes water saltier. The ice does not incorporate most of the salt. > > This cold, salty water becomes dense enough to sink to the abyss. This > > happens, naturally, at the fringes of the Arctic and the Antarctic, > > during their respective winters. Under present conditions, all the > > northern hemisphere action in this business happens in the Atlantic. > > This drives the famous conveyor belt cartoon that you have probably > > seen a few times by now; it's important to note that it is a very > > crude representation and the truth is vastly more complicated than > > that (and more complicated than the wind-driven circulation, though I > > have also simplified that a bit.) > > Hmmm. > > It's commonly portrayed that way, but AIUI the input of work (done > against gravity) that really "drives" the circulation is actually the > mixing that takes place over the wider ocean basin, not the convection > at the northern end. This mixing is driven by tidal dissipation and > wind-driven currents over the ocean topography (preferentially over > ridges and around the edges of basins). Geothermal input may also play a > significant part, expecially in localised areas (heating from below is > very efficient at mixing fluids). > > > There is no evidence of the Gulf Stream "shutting down" at any time > > since there has been an Atlantic Ocean, and there is very little > > chance of such a thing happening. It would be interesting to trace the > > ortigins of this widespread misunderstanding. > > I think it's only to be expected - the Gulf Stream / North Atlantic > Drift / THC are basically the same thing in the public consciousness, > probably in many non-specialist scientists' minds too. > > James (not a bona-fide oceanographer by any means, but I have played one...)- > Hide quoted text - > > - Show quoted text -
What do you make of this quote?: "TIM FLANNERY: Well, look, those scenarios really deal with those big positive feedback loops, you know. The first is the shutdown of the Gulf Stream, which, if that occurred -- and, you know, the Gulf Stream runs along the US East Coast and up into the North Atlantic and brings a tremendous amount of warmth to Europe. We know it has shut down in the past. If it shuts down again, Europe will face very severe conditions, cold conditions. And that heat, of course, has to go somewhere, that was normally going north and being dissipated. My guess is it's going to go into the Gulf of Mexico and the southern Atlantic and cause more severe hurricanes and so forth. But, you know, we have to do more science on that to really justify that view." made on Oct 25 unless it was taped. http://www.democracynow.org/article.pl?sid=07/10/25/1454240 Flannery obviously thinks its OK to say this. Is this: 1. Correct 2. Acceptable informal lay communication 3. A gaffe ? --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. Global Change is a public, moderated venue for discussion of science, technology, economics and policy dimensions of global environmental change. Posts will be admitted to the list if and only if any moderator finds the submission to be constructive and/or interesting, on topic, and not gratuitously rude. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/globalchange -~----------~----~----~----~------~----~------~--~---
