Quote:

There have been significant chunks of ice melting and breaking off of the Artic ice pack at the North Pole and in Antarctica, but this isn't such a big deal, because it is salt water, which doesn't dilute ocean thermalclines like the Gulf Stream (although it will help global sea levels rise).



I was reading through these old posts and I thought I would jump in here. Since a lot of skepticism about GW is based on misinformation I wanted to clear up the logic used above.

All sea ice is, for the most part, made of fresh water. Sea ice forms from the bottom of the ice sheet. As the sea water freezes and crystalizes on the bottom of the ice pack, the salt drops out. Salt crystals aren't compatible with water ice crystals. The water directly under the ice becomes super cold and super saturated with salt.

You are probably saying "So what? Why bring up this technicality?" The reason is that super cold, super salty water sinks to the bottom of the sea. It displaces bottom water, pushing it away and forming bottom currents that circulate all around the globe. It's the main driving mechanism for thermal haline circulation, or the ocean bottom conveyor. It eventually causes upwelling of bottom nutrients in other areas like the Grand Banks and areas off Europe. These bottom currents even make their way as far as the north Pacific. We can tell this is true because we have age dated the water using carbon-14. The further we get from the areas of sinking, the older the bottom water.

This sinking of surface water can't happen in non-arctic waters because of thermal layering. Remember how the Red October hid under the thermoclines? There are only two main areas where bottom water is formed (ie cold, salty, surface water sinks to the bottom) and those are the Weddell Sea off the coast of Antarctica, and in the Arctic Ocean the off the coast of Greenland. Both areas are showing signs of pack ice collapse. What happens if one of the main drivers for ocean circulation goes away? Nothing good, I suspect.

Oh BTW, pack ice contributes very little to sea level rise. The volume shrinks slightly as ice turns to water, and pack ice is 9/10s submerged to start with. As ice melts it adds no volume or level change to the the water that it is floating in. The 6 inches or so of sea level rise that we have seen in the last 50 years is attributed mostly to thermal expansion.

Well, just my 2 cents worth.

I was born a long ways from where I was supposed to be. - Bob Dylan