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How do ice cores preserve temperature records? Cores drilled through the icecaps in Greenland and Antarctica are our best records of the climate over the last 800,000 years. The best cores literally have 1 band of ice per year, so the ice in each core can be precisely dated. The chemistry of the ice can then show whether there were glaciers present or not….but how do geochemists do that?
Let it snow, let it snow, let it snow!
There are few things more beautiful than the intricacy of a snowflake, but how exactly are they formed? Why are they symmetrical? Why are no two the same?
Let’s find out!
The birth of a snowflake:
Snowflakes form in cold weather when water droplets in the atmosphere freeze onto a particulate; perhaps pollen or some dust. As the particle has now gained a bit of weight (don’t we all over the holidays?), it begins to fall towards the ground. As the ice crystal is falling, water vapour freezes onto it, building new crystals and laying the foundation for a snow flake to form. The temperature at which a crystal forms and the humidity of the air determines the basic shape of the ice crystal. For example, we tend to see long needle-like crystals at -2 degrees C and very flat plate-like crystals at -15 degrees C.
Symmetry!
Many snowflakes are symmetrical; this is due to the crystallisation of water molecules. When water molecules are in a solid state, such as in ice and snow, they form weak bonds (called hydrogen bonds) with one another. This process means that they arrange themselves in predetermined spaces which results in the symmetrical, hexagonal shape of the snowflake.
No two the same?
If you take into account the number of water molecules and isotopes of oxygen and hydrogen, then it is safe to say that no two snowflakes are identical. However, it is possible to find two that look pretty similar, but even this is a huge improbability- I definitely wouldn't recommend spending your life trying to find snowflake twins!
When you think about it, each snowflake will follow a slightly different path through the atmosphere and will encounter different conditions along its journey; so they all tend to look unique- more diversity to awe at!
-Jean
Images courtesy of Alexey Kljatov
natgeotravel Video @ladzinski / A freshly rolled iceberg is a pretty special thing to see. It looks like a flawless patch of sparkling crystals. We spotted this iceberg from about a mile out, floating in a fjord like a big chunk of sapphire.
Beautiful Sun Pillars Sun Pillars occur typically during sunrise or sunset, when sunlight is reflected off the surface of falling ice crystals associated with thin high-level clouds, like Cirrostratus clouds. The crystals are hexagonal, plate-like crystals and as they fall they are forced into a horizontal orientation due to resistance from air. These crystals must be similarly oriented and slightly tipped with respect to the viewer in order for a pillar to be observed. The result is the reflection of this beautiful pillar of light. Sun pillars are initially the same colour and width as the sun, but they will gradually change colour from orange-white to red-orange (at sunset) as the shorter wavelength colours like blue and green are being preferentially scattered from our view. -Jean Image Credits: Top image: Rick Stankiewicz taken in Keene, Ontario, Canada Bottom left Image: Jim Foster taken north of Baltimore, Maryland Bottom right image: Kevin Ponez taken near Jenison, Michigan
Thick snow covering a Swiss Forest and Mountain Valley
Interesting patterns of ice on a cold December morning.
Steam venting from a fumarole in the distance, snow covered landscape, Iceland.
Polar Bears Hangin’ Out
This family of polar bears was photographed resting on the Arctic Sea Ice. I found this photo particularly interesting as it shows some of the details of the sea ice in the Arctic, particularly the blue color.
When ice forms, it typically has air bubbles in it (seriously, go check any ice cubes in your freezer right now if you’d like). These bubbles interact with light moving through the ice and give it the classic pale white color seen in most ice. On the other hand, when you have a slab of ice that appears blue, it’s a sign that most of the air bubbles have been removed. Once the scattering bubbles are removed, the ice looks blue for the same reason water does - that is the color of light that transmits most easily through the ice.
For there to be blue sea ice, it probably means these bears are sitting on wedges of multi-year ice. Every year, some portion of sea ice in the arctic melts and refreezes, but other portions break up and are piled up by the wind into thicker slabs. These thicker slabs can endure several years of warming and cooling without totally melting, and a repeated cycle of warming and cooling ice can remove the bubbles that make it appear white.
Multi-year ice is more stable as it tends to be thicker. As there is less surviving multi-year ice, the whole ice cap in the arctic becomes less stable. When there’s a major ice melting event, as is ongoing right now (see here: https://tmblr.co/Zyv2Js27uordb) it doesn’t just reduce the ice extent that year, it also leaves the whole ice cap more exposed to breaking up in future years.
And yes, the cubs are kinda cute.
-JBB
Image credit: USGS https://flic.kr/p/HKhFJh
Reference: http://www.webexhibits.org/causesofcolor/5C.html
Spectacular work with the snowflake photos in this set. (CC licensed).
Delightful time-lapsed video of ice crystals growing and shrinking taken under a binocular microscope with crossed polars (a polarizer above the sample and below the sample so that light is only visible if it moves through a crystal that changes the direction the light is moving).
Snowflake
H2O is a fascinating substance. It is literally the only species found on Earth in liquid, solid, and vapor states under common conditions. H2O ice meets all the definitions of a mineral – solid, crystalline structure, etc.; but it’s a pretty neat mineral since it occasionally falls from the sky! (Seriously, during this week’s snow storm, can I get anyone to run outside screaming that minerals are falling on them?)
The shape of many minerals gives information about how they formed – did they grow slowly and develop strong crystal faces or did they grow rapidly and develop irregular edges? Snowflakes behave the same way – the shape, size, and texture of the ice crystals are related to how they form.
Simple hexagonal prisms like these are some of the most basic snowflake shapes – other types can grow around cores in this shape. These snowflakes also look fuzzy due to rime, formed by fog freezing to the edge of the already-growing ice. Continued rime growth could take this snowflake from having a crystal shape to being a much more irregular pellet.
This single snowflake has been magnified using the US Department of Agriculture’s electron microscope facilities.
-JBB
Image credit: USDA Electron and Confocal Microscopy Laboratory http://discovermagazine.com/galleries/2015/jan-feb/snowflakes
