Tuesday, June 17, 2008

CCSM Paleoclimate Ordovician

This is presented by Christine Shields of NCAR. She is speaking on her simulations of he Late Ordovician. This is also done with Dr Scotese of the paleomap project and Dr Kiehl of NCAR. She is exploring why the Ordovician Extinction is interesting. This is the only extinction to take place during glaciation. This causes a very mixed ocean and this apparently brought up toxins from the sea bed as well as provide lots nutrients. Algae go nuts making more toxins. Causes extinction.

Ice extent is close to the subtropical during the time period and reaches up to 30 deg s. There are no continents in the northern hemisphere. They literature seems to indicate a high CO2 content, 15x pre industrial. This is a big dilemma. How do you get glaciation with uber carbon dioxide? They ran with T31 resolution for 100 years. They chose a cold orbit with low eccentricity. They found that solar forcing seems to be 15.5 watts/m^2 total. Model seems to be a proof of concept: first time for a fully coupled model on the Ordovician.

Poles are warmer than now in the simulation. This is a warm world. They actually get a very strong circumpolar current: something like a roaring 40s there. The ocean mixing is extremely strong. Northern hemisphere overturns down to the very bottom of the ocean. Polar regions seem to show that it takes 10 years for overturn (ideal age). Modern Atlantic is 31 years +/-.

They're changing the model. Adding ocean topography and adjusting the CO2 estimates: they need to get the ice to grow, don't get it yet. They think they will get it. Shields is very optimistic. because of the weathering outbalancing the dominating the solar forcing. They need to change the ground cover model.

I'll save commentary until later.

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