a window to the ocean

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I was sitting on the back of the ferry the other day, gazing through a fairlead, and I started thinking about what if that were all I could see of the Ocean. If I could travel anywhere on the ocean, but I could only look through that small window...

Fairlead: a fairlead is a ring through which you pass a rope that changes the ropes direction with minimal friction. You can see it in the picture from the ferry: it's the small window through the side of the ship, right next to the cleat (the big yellow thing). PS. Don't feel bad for not knowing what a fairlead was. I just spent the last 20 minutes figuring out what the name was for little window that inspired this post.

Thinking about my small window to the ocean, I realized it would take forever to see anything. It would take months (years?) to cover just Casco Bay, forget studying the whole ocean with my little window. This got me thinking: as an oceanographer, how much of the ocean we can see at any given time? 

Well, put it this way, it's not a whole lot different than looking at all of Casco Bay through the fairlead on the ferry.

First, I looked at the average volume that's measured in a typical BATS (Bermuda Atlantic Time Series) plankton tow and found an average filtered volume of about 500 m^3 (n=479, thanks Jonathan for that data).

An approximate value for the volume of the ocean (from Nnybakken and Bertness's Marine Biology) is 1,370 * 10^6 cubic kilometers. That's 1,370,000,000 km^3, over one billion cubic  kilometers of ocean water!
On a percentage basis, a typical BATS plankton tow, which generally sample the top 200 meters or so of the water column (personal comm.) covers less than even a percent of a percent of a percent of the ocean (~3.8*10^-14%). This means that a common tool we use for looking at the ocean barely covers anything!

Well, what about satellites? They can get a much bigger picture of the oceans in a short amount of time. MODIS circles the earth 20 times a day and can cover the entire planet with it's beams about every day or two. One piece of data oceanographers get from MODIS is sea surface temperature. Let's say that for the sake of this calculation the sea surface temperature is representative enough to give us a picture of ocean temperatures in the top 100 meters (about a football field in length) of the water column. 
The surface area of the ocean is ~335*10^6 km^2, or 335,000,000 square kilometers. That's about 70% of Earth's surface area. If you multiply the surface area of the oceans by 100 m that will give an approximate value (likely an overestimate) of what MODIS can see, which is about 335*10^5 km^3 (and yes, not all the ocean is 100m deep, but more than enough is to make this calculation interesting). 
If you divide that value by the total volume of the ocean, you get: 0.024, which means MODIS can see only about 2% of the oceans as far as the total volume of water.
 If you went to a baseball game at Fenway park and you could only see 2% of the field, that's like seeing only the portion covered by the red square in the infield in the picture below (calculated as 2% of the fair territory, which is 2% of 99,000 sq ft or ~2000 sq ft).

The point is, the ocean is HUGE and even our best tools can't see much at any given time. So, as scientists we need to come up with effective and innovative ways of looking at it. It also means that there's a lot of ocean to explore. That's the cool part.

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Nice analogy. Interestingly, if you ever watch baseball on TV, we spend almost the entire time focused on that little red square. If you know how the system works, you can sample a small percentage and still have a good idea of what's going on.

Very cool post!

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This page contains a single entry by Peter Stetson published on April 8, 2010 4:16 PM.

Five to one... sometimes odds are not favourable. was the previous entry in this blog.

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