Archive for the ‘Theory’ Category

A good week for defense

January 19, 2015

I successfully defended my dissertation last Thursday! Defense title: “Measured and modeled albedos of sea-ice surfaces on the oceans of Snowball Earth.”

Here’s how I summed up my talk:

A planet orbits round a yellow sun
Light years away or megayears ago
Its seas are dark, its continent is dun
But brilliant sea ice sets its pole aglow

Its CO2 drops dangerously low
Tendrils of ice reach from the polar caps
That sparks a feedback: oceans turn to snow,
Glaciers push in to close off any gaps

The oceans roiled with countless living cells
Who learned to take their energy from light
Now locked beneath the cold of Dante’s hells
They starve; how long must they endure this night?

Why has this happened, and by what device?
To know, we must investigate the ice.

As sea ice freezes, tiny drops of brine
Are trapped between the quickly forming plates
When cold enough, their molecules align
Into sodium chloride dihydrates

The solid crystals catch and scatter light
Reflect it back, refuse its energy
And I myself have quantified how bright
The surface of the sub-eutectic sea

And in our lab we’ve watched salt ice sublime
With instruments ingeniously designed
The secrets of another space and time
Unfold beneath my models and my mind

This is my work; I hope you will agree
That it is worthy of a Ph.D.

Repost: Cracks and Bubbles

February 8, 2011

Original post, called in on January 13, 2011. Thanks once again to Jonathan Beall for the transcription!

“Hi. Today was a quiet day. Well, in terms of activity. It was a quiet day in terms of activity because it was a noisy day in terms of wind. We had a good day of spirited scientific discussions in the tent instead. We were mostly discussing bubbles and their contribution to the amount of light reflected from ice, or its albedo.

Bubbles are awesome.

Ice is very transparent. Light can travel a long way before it gets absorbed. If there are no bubbles in the ice, most light will just travel straight through, and the albedo will be low. If there are bubbles, though, light can hit the bubbles and bounce away in a different direction. A lot of the light that goes into the ice will end up bouncing right back out, which is why bubbly ice has a higher albedo than clear ice. Ice in glaciers and on ice sheets, like where we are, has lots of bubbles because it’s formed from compressed snow. The spaces between snowflakes at the surface will turn into bubbles as the snow is squeezed into ice and a small amount of the air remains behind as bubbles form.

Complex bubble shapes are partly a result of the complex shapes in the snow crystals that formed them.

We also talked about cracks in the ice, which can increase the albedo just like bubbles do. The blue ice here has lots of cracks in it, mostly quite thin. We think they form partly because the ice is cracking as it moves, and partly because, as the top of the ice erodes away from the constant wind, the ice lower down is no longer under as much pressure, and it expands creating more cracks.

Cracks in the ice (picture taken using the Crack Box, an invention I'll explain in a later post)

We actually put on our parkas and went out to look at the ice near camp to see how the cracks behaved and to figure how we might account for them in our measurements. We probably looked a little silly lying face down on the ice and wriggling along the ice like seals, but then science is frequently a little silly; that’s one of the reasons I like it.

Another incident of science being silly.