Thursday, November 24, 2011

22 November – Shrinking Cups...

Styrofoam cups are decorated before being placed on the MOCNESS which went down to 1500 m. See the effects of the pressure at this depth on our cups at the end of the blog. ET Kris drew the awesome cup on the left, your author (and practicing non-artist) drew the magnificent turkey on the cup on the right.
Yesterday contained one of the most unusual traditions aboard oceanographic research vessels (compared to any other kind of ship) which was the Cup-Cast.  As you go down into the ocean, the pressure around you increases dramatically. At 10 m depth, an additional 1 atmosphere of pressure is pushing in on any object at that depth (the atmospheric pressure at the sea surface = 1 atmosphere – sometimes scientists do keep things simple and straightforward). However since water is much more dense than air, you get very rapid increases in pressure as you go deeper (1 atmosphere for every 10 meters you go down). This is why a lot of oceanographic instruments are placed inside pressure housings (metal cases that are designed to withstand the increased water pressure).

The ship's lounge is full of budding artists, colorfully decorating their souvenirs of the abyss.
If you have scuba dove (or even dived to the bottom of a swimming pool), you've experienced the increased pressure – most notably in your ear (which you can equalize by pinching your nose and trying to blow gently outward).  The increased pressure of the water is trying to squeeze the air inside of you and the pressure difference between the air pockets within your body and the outside are what causes that discomfort.

 Chief scientist  Ann Bucklin decorates her cup – which I believe contained a drawing of a chaetoganth (a zooplankton).
But there's another interesting feature of the pressure of the ocean deep. If you take a normal styrofoam coffee or drink cup (which is composed of cells of foam that are air-filled), and send it down deep, the air gets compressed out of the cells and the entire cup shrinks.

 More artists at work, MT Krista (left), MST Melissa P. (background), and non-MST Melissa M. (foreground) use markers to draw various designs on their cups.
So oftentimes on the deepest CTD cast or net tow of a cruise, all the folks on the boat will decorate cups that are placed in a mesh bag and attached to the instrument going down to the depths. And what comes up is a miniature version of what you designed.  Not to spoil the surprise, but if you know somebody on this cruise, you may be getting a cup as a holiday gift in the next month...

 And here are the post-cast cups. They shrank by about 80%. These were my cups so you can see why I'm a scientist and not an artist, although many of the other folks on the crew drew some really beautiful pictures on their cups.
On the science front, we've finally gotten several consecutive days of not-super-strong winds or rough seas, so we've been able to conduct our stations in a timely manner. This afternoon, I also did my second small boat survey which saw lots of aggregations of krill in the water column (including both patches of large adult krill, and smaller layers of juvenile krill). I wasn't the only one checking out these krill patches, as three humpback whales and a dozen or so Gentoo and Chinstrap penguins were in the area. The penguins were diving down and surfacing in a pattern consistent with feeding on the krill swarms below us!
Hope everyone has a good Thanksgiving Holiday!