Ice Cores: Part 3 Dust and Ashes

Continued from Part 1 and Part 2

Layered Snow Melting

I was going to move right on to the dusty stuff in the ice, but ran into some very interesting University study pages I have to point out.  Columbia opens its mathematical calculation class with an introduction we’re going to look at:

“These annual layers provide a record of the earth’s climate that reaches back as much as 200,000 years.”

What?  I thought they went back 1.4 million years!  That is one giant discrepancy.

Columbia recommended their students check out this U. of Michigan (go Wolverines!) page.  The coolest thing is a cross-section drawing showing a lake (as in unfrozen water) “the size of Lake Ontario” underneath the 4km [13,000ft+] elevation Vostok Ice Station in Antarctica.  That is awesome.  Anyone for a swim?  Oh, yes, the U. of Mich drawing states the ice goes back 420,000 years.  All right, what’s going on?

Have a look at what they say about the squashed bottom ice:

“The… age of the ice… is obtained by counting layers of ice and, when layers are no longer clearly visible, modeling the flow of merged ice layers.”

Wait a minute.  In really squashed ice, “layers are no longer clearly visible?”  I don’t remember the Natural History Museum tell us that.  What is this “modeling,” and is this going to end up being as full of assumptions as radiometric dating is?

I searched nearly an hour for a page that would explain how you figure out a model to calculate “the flow of merged ice layers.”  If any of you know what they’re talking about please leave a comment!

Snow layers

The other, better known way scientists study really deep, squashed ice from an ice field is by looking at the layers of “dust.”  Today we’re going to find out what this dust is and where it came from before settling onto Antarctica or Greenland.

The best page I found on this is a technical paper abstract.  Those are the high-falooting, jargon filled short versions of what the scientists were studying so other scientists can keep up with what they need to know in a few minutes.

Major features in Antarctica: (1)South Pole, (...

(9) Ice core drill sites (EPICA), (16) Lake Vostok (Photo credit: Wikipedia)

They were studying an ice core from Antarctica using a core called EPICA Dome C.  First, they say they’ve been using X-rays to study the dusty ice.  Cool.  Then they go on to their ideas about the climate at different depths of the ice.  I’m with them for one Ice Age, but that would be near the bottom, not where they put it.

Turns out, the stuff blown onto the ice has changed a lot from time to time. A lot of the dust at certain levels has the same ingredients as dirt at the bottom of South America.

At other levels there is dust from lots of different sources.  The study authors are pretty sure some of that mixed dust came from Australia.  I also found a similar study from Greenland saying the dust up there is either local or blown in from East Asian deserts.

But this isn’t the whole story.  When a large volcano erupts with a lot of ash, the tiny particles are carried by the wind to the ice sheets.  Even in recent times, volcanic ash has been suspended in the air around the globe for many months by eruptions like Krakatoa’s in 1883. Another helpful thing is that every volcano spews out different things.  I don’t usually use PBS:NOVA because it is so biased, but they were the clearest on what’s going on:

Snow-like ashfall caused by heavy rain mixing ...

Snow-like ashfall caused by heavy rain mixing with ash columns

“Ash from a particular volcano has its own unique characteristics, much like a person’s fingerprints. These characteristics include chemical composition, and the size and shape of crystals and glass shards. They can be used to determine not only the particular volcano that produced the ash, but the particular eruption from that volcano as well.”

So a really major eruption will leave traces in the ice on all the ice sheets.  Scientists use these layers to check if they are counting at the same rate as other researchers.

BTW, this doesn’t always work.  A moving ice sheet (glacier) in Alaska didn’t have ash from an 803 AD volcanic eruption as expected, leaving scientists to try and figure out why.

What they don’t tell you is that the other records they are comparing with don’t
have dates on them either.  Once we move beyond written history, it is
all guesswork to calculate how old any of these layers are, whether they are ice sheets, ocean floor layers, or anything else.

The LORD is slow to anger, and great in power, and will not at all acquit the wicked: the LORD hath his way in the whirlwind and in the storm, and the clouds are the dust of his feet. Nahum 1:3