Wednesday, May 23, 2007

Motion through the Ocean

Things move through the ocean in funny ways. Chemicals, nutrients, fish poop, whathaveyou. This stuff doesn’t just sink, but it moves along laterally with the currents too. Advection and Diffusion are two ways that things move through water and will be our topic for discussion today.

Advection is considered “Directed Velocity”. Just movin’ along in a straight line. How we describe advection is by flux. Advective flux is velocity (in meters/time) multiplied by Concentration (in moles/volume). The units of flux are moles/area-time.

Let me refresh your memory on what a “mole” is. A mole, in the chemistry realm, is a shitload of atoms (6.022 x 10^23 atoms to be exact). We can convert from moles to mass if we know an element’s atomic weight.
Look at our periodic table of the elements. See that number with a bunch of decimal places behind it? That’s the atomic mass. One mole of that element weights that many grams. For example, the atomic weight of Germanium is 72.59 so a mole of Germanium weights 72.59 grams. That’s 20.74 eightballs of Germanium to a mole. Don’t do drugs, kids.

Advection is a great way to describe stuff that is sinking. Diffusion on the other hand tells you about how things are spreading out. Diffusion is “Random Motion”. Remember that whenever you have a big glob of something that is really concentrated, like pee-pee in a swimming pool, it wants to move from an area of high concentration to low. We describe diffusion using Fick’s First Law.D stands for “diffusivity” and is in units of area per time. This law is also really great if you want to describe eddy transport. Eddies are big, swirly, chaotic regions of fluid movement. You can see them when you put cream in your coffee. The fluid mechanics within those eddies are hard to describe because the movement is so random, but the transport of particles via those eddies can be figured out using Fick’s first law.

Want to know more about this mysterious Fick? Adolf Eugen Fick was a 19th century
German physiologist who defined laws that we use for diffusion. He also invented the contact lens.

Kind of an intense lookin’ dude. It’s interesting that the man who invented the contact lens came up with laws that we use for Geochemistry. Laws that I will be grilled on during my Qualifying Exams. Thanks buddy.

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