CTD Deployment

You’ve seen the data that comes from doing a CTD cast. But how do we actually collect the data? We have to put the CTD in the water very carefully, to avoid damaging our instruments or our ship. To do that, we use a winch, which includes a pulley (remember those, 6th graders?). Here’s a video of the process:



A few highlights:
- The guy making the funny hand signals is Drew. He’s our Resident Marine Technician, or restech. The hand signals tell the winch operator what to do.
- That’s me in the lower right corner! I’m running a tag line, one of the ropes that keeps the CTD from swinging too wildly. There’s not much risk when the seas are calm like they are in this video, but you can imagine what happens in rough seas. The other tag line is run by Gerald, who is a member of the Philippine Coast Guard.
- Look at the CTD going down in the water. Can any of the 7th graders tell me what is happening to the light underwater to make it look like that?
- I left the soundtrack as it was so that you could hear what we hear. Ships are loud places.

Finally, thanks to Alette for filming!

Sightseeing

I go to sea for the science, but one of the things that keeps me coming back is the beauty of working on a ship. I’ve been giving you a lot of data recently, so I want to balance that with some of the sights I’ve been seeing.

This is a boat loaded up with boats! I’ve never seen anything like it before:


This is last night’s sunset. It was spectacular:


And here is tonight’s sunset – just a day apart but very different:

The Cups, Part I

The first batch of cups is back! I have to sink them in batches of about 50 because I don’t have a bag big enough to hold them all. We sent them down at station 49, located at 8°45’ N, 122°44’E. Those numbers after the degree symbol are called minutes, and they represent parts of a degree. There are 60 minutes in one degree, just like there are 60 minutes in one hour.

So how did they turn out? Well, here they are in the lab…

And here they are in the bag (the green tape keeps them from getting stuck together)…


And here’s my friend Drew securing them to the CTD frame…

And here they are with my friend Jake’s good-luck bracelet that he wanted sent down too…


And here’s the CTD going into the water…


And here they are, safe on the ship…

And here I am, cutting them off the CTD to bring home to you!


Look how empty the bag seems to be! It’s the same number of cups that I started with; they’re just very small. You know that their size has decreased, what do you think has happened to their density?

Science Club Q & A

Hi 6th grade science club! I hope everyone did well on their final exams. I wrote a separate post on seawater and density, but here are some answers to your other questions:

Irving – I was seasick, and it was terrible! We had rough seas for a few hours and I felt awful. But now I’m better.

Daniella – I’m eating fish every day, but it’s not local fish. We’re only allowed to go fishing when we’re far away from land or fishing boats, and that’s not too much of the time. We should have some good fishing later on in the cruise though.

Bryan, Nachary, & Andrea – Your cups are safe in my room. I’m going to sink them once we’re out in the Sulu Sea, which is deeper than where we are now. And I promise to take plenty of pictures.

Shaina – I have not seen any sharks, but my friend Drew saw one. I’m sorry that I missed it. But I have seen squid and flying fish.

I do have a sunburn even though I’ve been wearing sunscreen. But it’s not too bad. I’d like to see your barometers when I get back. We have a barometer on the ship too, and right now we’re at 1006.8 millibars.

Life at sea has been very busy because my ADCP cables keep breaking! It’s very frustrating. But at sea, when something breaks, you learn how to fix it. Here’s the rewiring we did:


It was a little like science club, since we didn’t know if it would work until we tried it. I know it looks weird, but it’s holding up so far!

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.

Cruising

The cruise is underway! Here is the view we had when we left Manila:


In order to leave Manila Bay, we needed a pilot to guide us out. Normally the word “pilot” refers to the person flying an airplane, but it’s sometimes used for boats, too. Because Manila Bay is such a busy place, the government requires pilots who know the bay very well to help the captains steer the ships. Here is the pilot boat on our starboard side:


Our what? At sea, you don’t use right and left to describe locations within the ship. It would be too easy to get confused – if you’re facing the back of the ship, then left becomes right! So we have four directions: forward, aft, starboard, and port. If you’re facing forward (the front of the ship), port is on your left, starboard in on your right, and aft (or after) is behind you. The front of the ship is called the bow, and the back is called the stern:


If your classroom were a ship, where would the bow be? The stern? What direction (forward, aft, port, or starboard) would you have to go to reach the door?