Mooring Recovery

Here's a video of the mooring recovery we did today. Drew, our
Restech, is going to tell you what's going on. First, here are some
definitions that will help you understand him:

- a mooring is a scientific instrument that gets attached to an anchor
and left in the ocean to collect data
- a buoy is something that floats in the water - in this case, it's
part of the mooring
- lifelines are cables that act as railings around the ship

Let me know if there's anything else that's unclear. Also, I'd like to thank Drew for doing the voiceover and Suzanne and Pach for doing the video recording.

Density & Seawater

Density can be a really hard idea to understand. To start, try thinking back to a time when you were in a swimming pool, and how hard or easy it was to float. Then think about floating in the ocean. It’s easier to float in the ocean than in a pool because ocean water has a higher density. As water gets more and more dense, it’s easier and easier for you to float in it.

So why is seawater so dense? And what changes the density of seawater?

1) Temperature. This is the big one. Cold water is denser than hot water. Remember drawing the molecules in solids, liquids, and gases? In liquids, the molecules aren’t as tightly packed as in solids, but they’re tighter than in a gas. High temperatures make molecules move faster, so they can’t stay close together. A hot liquid looks a little more like a gas, and cold liquid looks a little more like solid:2) Salinity. Salinity is a measure of how much salt is in the water. Salt makes water denser, but a change in temperature will have a bigger effect on density than a change in salinity will. The salt molecules keep the water molecules closer together by holding on to them through chemical bonds.

3) Pressure. Picture what each of those boxes I drew above would look like if you sat on them. All of the molecules would be pushed together! That’s what happens to the molecules in the seawater that’s down at the bottom of the ocean. The weight of all that water on top of them packs them tightly.

Here are plots of temperature, salinity, and density from our last station:
A few tips to help you understand these graphs:
- The units for pressure are “db” which stands for decibars. The cool thing is that in the ocean, a decibar of pressure is equal to a meter of water. So when you see 100 db, you know it’s 100 m down.
- The units for salinity are “psu.” That stands for practical salinity units, which doesn’t really mean anything at all. So don’t worry about it! Just remember that higher numbers mean saltier water.
- The units for density are kg/m³. That tells you how much one cubic meter of water would weigh. So when you see a density of 1030 kg/m³, that means that one cubic meter of water (about 260 gallons) weighs 1030 kg (about 2,270 pounds). For comparison, tap water at room temperature has a density of about 1000 kg/m³.

So if you were holding a gallon of tap water, it would weigh 8.3 pounds. But if you were holding a gallon of seawater, it would weigh 8.6 pounds.

Station 22

Life on a ship can be lots fun, but we also work very hard. By now you’re probably wondering what we do all day. Most of the time, we do CTD casts. CTD stands for conductivity (a measure of how salty the water is), temperature, and depth. We put the instrument package, which contains the CTD, LADCPs, and few other things, into the water on a very strong wire. Here’s a picture of the CTD on the package:


It’s the odd-looking thing in the middle of the pictures with all of the wires attached to it. You can see one of the LADCPs on the left.

Later, I’ll try to get a video of the deployment (when we put the package in the water) and recovery (when we take it out of the water). For now, I’m going to show you the data from a recent CTD station, number 22.

Normally we can’t distribute data from a cruise until two years after collection. Since we did the work, we get to publish our interpretations of the data first! However, the chief scientist of the cruise, Dr. Arnold Gordon, is letting you have the data early as long as you promise not to publish before he does.

Here’s a graph of the temperature data:

There’s a lot we can learn from this graph! First, look at the axes. What are the units? How big is the range? Look carefully at the y-axis and the direction in which numbers increase. Is this how we usually make graphs?

Once you know how the graph is structured, you can start working with the data. What happens to the temperature as you go deeper in the water? Does it increase? Decrease? How quickly does the temperature change with depth? Why does the temperature change in this pattern?

Remember, this is the temperature during one cast. Would we get different results if we tried it again? What about a cast nearby – would the results look the same? There are a lot of questions you can ask about these data. Let me know what questions you want to answer, and I’ll try to supply the data that you need.