Diving
I'm back in New Zealand after a week in McMurdo frantically working to get field gear sorted and returned, plus documenting and organizing field data and ideas while I still had Ian to work with. I still have lots to say about the trip, so I'll keep posting things about the field work for a while.
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I spent a lot of time dive tending while Ian and Dale dove under the lake ice. There are two essential jobs above the ice when someone is diving: 1) Watching the air levels and communicating with the diver via the control box; and 2) feeding out and taking in the air and communication line. Sometimes I’d do the air/communication job, particularly when there were numerous scientific notes to take.
This job can be anything from very enjoyable to extremely uncomfortable depending on the weather. One has to stand in the open between the dive hole and the reserve line, feeding it out as the diver goes farther from the hole and pulling it in (wet) when the diver gets closer. Often, the diver doesn’t say exactly what he’s doing, so you have to pay attention. If the line gets too loose, it can get tangled around other things in the water or get loops that are disorienting for the diver. If you hold it too tight, the diver tells you. Sometimes they want extra line. For example, when Dale is taking photos, it’s really important that the line isn’t so tight that it pulls him the wrong way in the water. Or when Ian is adjusting a microelectrode in the sediment, pulling on the line could cause him to turn and disrupt the experiment. If they start swimming back toward the hole without telling you, line can pile up. Sometimes the only sign that you need to pull line in is that it’s floating up into the hole on its own! Then you have a lot of work to do quickly.
When you pull in line, it needs to be wound neatly so that you can feed it out again without tangles. We wound it into a figure 8 on a sled to keep it off the ice. Sometimes, when I’d get behind, I’d end up with extra twists. It’s nice to have help keeping the line neat when the diver is coming in from a long ways off.
Some of the other dive tending jobs including feeding out rope that is attached to instruments the divers are deploying, handing the diver various items like cameras or core tubes, and taking things like cameras and cores from the divers.
Ian and Dale did various things under the water. Dale is an excellent photographer, and he had several dives that focused on taking video of the various microbial mats and structures. They are beautiful. Ian tends to focus on detailed manipulation of equipment and scientific observations. He has the patience and ability to control his motion underwater well enough to put expensive, delicate microelectrodes into the microbial mat to measure O2 concentrations and pH. Sometimes he manipulates them by hand, such as in this experiment.
However, for this trip, we were able to borrow Hal, an underwater microelectrode manipulating robot.
Hal allows us to manipulate the microelectrodes from the surface rather than having to do it by hand while under water. We lowered Hal to the bottom of the lake. Then Ian or Dale would dive down to him and inflate an air bag to lift him off the bottom. They would then swim Hal to the location we wanted to study and lower him by releasing air. Once Hal landed on the bottom, the diver would uncover and reposition the microelectrodes. If all worked well, the electrodes would not break, and Ian would send commands down to Hal to move the electrodes and they he’d write down the results. Hal is supposed to be able to position the microelectrodes automatically as well, but when we tried this, the electrodes broke, so we worried that he moved them sideways while they were in the mat.
Another common job for the divers was to collect samples. We did this in three ways. For some of the carbonate structures, the divers could tilt them over into boxes that they would seal underwater and bring up to the surface.
For softer mat that was thick, it worked well to take a piece of clear plastic pipe, push it into the sediment, and put rubber stoppers in both ends as it’s pulled out.
These cores were our most common samples. In places where the mat was thin and had coarse sand or gravel below it, the cores didn’t work. For these samples, the diver would use the core tube to cut through a section of mat and then waft the mat into the core tube sideways. For very thin samples, Ian used a small Nalgene bottle with the bottom cut off to cut through the mat, and he put the cutouts into boxes.
Dale also did a couple of dives where he swam instruments around under water to map out variations in light and chemistry. These sorts of dives are ones that require a lot of note taking because approximate locations and sometimes instrument values have to be recorded. We used the time of observations to provide data to correlate to chemistry measured by the instrument. We haven’t gone through these notes yet to see how well we did. That’s a job for the months between now and the next field season.
Ian ended his underwater time with an epic dive in which he did 3 dives worth of work in a bit less than an hour. We melted a second dive hole and decided to use it as a reference for changes over the next year.
Ian had put in a transect line the day before to mark a specific area that could be documented this year and again next year. It was held in place by bamboo stakes and had floats to keep the line off the lake floor. Ian started the epic dive by adjusting the line, placing the floats in good places, putting in a bamboo stake that had come out, and pounding in the end stakes with a hammer. (Think about how hard it would be to pound something into sandy ground underwater. With nothing much to push against, conservation of angular momentum causes some difficulties we don’t have on land.) Ian then swapped the hammer for a camera and photographed each of the areas with either a meter mark on the line or a bamboo stake in the lake floor.
After that, he deployed 6 sediment traps to see how much sediment settles out in the next year. This was a lot of work. I could tell it was hard as I tended the dive line. Ian was constantly moving back and forth, up and down. And he wasn’t talking. I paid very close attention to the tension on the line, trying to keep it exactly right so it wouldn’t interfere with his work. Luckily, it was a beautiful day with little wind, so it was very pleasant to be standing on the ice, and it was easy to concentrate.
The diving was very challenging. First, the divers are under the ice with only one way to the surface. They have to always keep that in mind. Second, they are wearing full face masks with a tether to the surface. The face masks restrict visibility to only straight ahead.
The tether (or air and communication line) can get tangled around things, can get in the way, and if it’s too tight, can pull the diver. Third, the water is just about 0°C. It’s cold, even with a good, insulating dry suit on.
Fourth, the divers can’t touch the bottom of the lake without stirring up mud that clouds the water. They try to touch the bottom as little as possible. Fifth, the work requires very careful buoyancy control. The divers are weighted with lead weights to help them sink, and they add air to their dry suits to help them float. Work near the bottom without touching it requires that the divers perfectly balance the amount of air they have in their suits. The air compresses when they go deeper because the pressure is greater (PV = nRT so if P (pressure) increases, V (volume) has to decrease because the number of air molecules (n) and temperature (T) stay the same; R is a constant). To increase the volume to help them float, the divers add air, e.g. they increase n. However, if they go shallower in the water and n is still high, they keep going up faster and faster. Thus, the divers have to let air out of their suits. Doing this precisely is an important skill, particularly since there is one more complication: breathing! Breathing in has a similar effect to putting air into the suit, and breathing out does the opposite. Thus, divers tend to move up in the water when they breath in and down when they breath out. Often when Ian or Dale was doing something delicate, they would hold their breath, sometimes taking in a bit more or letting some out to get their position in the water exactly right.
Sixth, some jobs required several instruments and tools. Some of these float and some sink. Keeping all of them under control when you can’t necessarily set them down and have them stay put is a challenge in itself.
Seventh... I think you get the point. I’m in awe of how much Ian and Dale got done under water!
_____________
I spent a lot of time dive tending while Ian and Dale dove under the lake ice. There are two essential jobs above the ice when someone is diving: 1) Watching the air levels and communicating with the diver via the control box; and 2) feeding out and taking in the air and communication line. Sometimes I’d do the air/communication job, particularly when there were numerous scientific notes to take.
This is me taking notes by the yellow coms/air control box. It was a cold day as you can see by how many clothes I'm wearing even though I was sitting inside the tent. The person handling the line was standing out in the real cold.
Most of the time, however, I tended the line.
This job can be anything from very enjoyable to extremely uncomfortable depending on the weather. One has to stand in the open between the dive hole and the reserve line, feeding it out as the diver goes farther from the hole and pulling it in (wet) when the diver gets closer. Often, the diver doesn’t say exactly what he’s doing, so you have to pay attention. If the line gets too loose, it can get tangled around other things in the water or get loops that are disorienting for the diver. If you hold it too tight, the diver tells you. Sometimes they want extra line. For example, when Dale is taking photos, it’s really important that the line isn’t so tight that it pulls him the wrong way in the water. Or when Ian is adjusting a microelectrode in the sediment, pulling on the line could cause him to turn and disrupt the experiment. If they start swimming back toward the hole without telling you, line can pile up. Sometimes the only sign that you need to pull line in is that it’s floating up into the hole on its own! Then you have a lot of work to do quickly.
When you pull in line, it needs to be wound neatly so that you can feed it out again without tangles. We wound it into a figure 8 on a sled to keep it off the ice. Sometimes, when I’d get behind, I’d end up with extra twists. It’s nice to have help keeping the line neat when the diver is coming in from a long ways off.
Neatly wound dive tether.
Some of the other dive tending jobs including feeding out rope that is attached to instruments the divers are deploying, handing the diver various items like cameras or core tubes, and taking things like cameras and cores from the divers.
Ian and Dale did various things under the water. Dale is an excellent photographer, and he had several dives that focused on taking video of the various microbial mats and structures. They are beautiful. Ian tends to focus on detailed manipulation of equipment and scientific observations. He has the patience and ability to control his motion underwater well enough to put expensive, delicate microelectrodes into the microbial mat to measure O2 concentrations and pH. Sometimes he manipulates them by hand, such as in this experiment.
The instrument in the upper center is a manual manipulator with a microelectrode attached to it. It's measuring O2 concentrations, which are recorded by the instrument on the lower left. The instrument on the right is measuring photosynthetic activity. This experiment was to evaluate how active and healthy the mats were. They were barely alive, producing almost no measurable results. To place this experiment, Ian first took out a large metal stake attached to a blue rope with the manipulator on it. After choosing a spot and getting it stable in the sediment, he came back to the dive hole for the micro electrode. He attached that and did a short profile in a carbonate structure. After repositioning the electrode, he came back for the PAM, which measures photosynthetic activity. He positioned that, made sure it was on and ended his dive. Hours later, Dale dove to the same spot (following the blue rope) and added a spot light on a tripod to the experiment to see if more light would change the activity. It turned out that the instruments had already stopped logging data, so we don't know if the light changed anything or not.
However, for this trip, we were able to borrow Hal, an underwater microelectrode manipulating robot.
Hal in the lab at McMurdo
Hal allows us to manipulate the microelectrodes from the surface rather than having to do it by hand while under water. We lowered Hal to the bottom of the lake. Then Ian or Dale would dive down to him and inflate an air bag to lift him off the bottom. They would then swim Hal to the location we wanted to study and lower him by releasing air. Once Hal landed on the bottom, the diver would uncover and reposition the microelectrodes. If all worked well, the electrodes would not break, and Ian would send commands down to Hal to move the electrodes and they he’d write down the results. Hal is supposed to be able to position the microelectrodes automatically as well, but when we tried this, the electrodes broke, so we worried that he moved them sideways while they were in the mat.
Another common job for the divers was to collect samples. We did this in three ways. For some of the carbonate structures, the divers could tilt them over into boxes that they would seal underwater and bring up to the surface.
For softer mat that was thick, it worked well to take a piece of clear plastic pipe, push it into the sediment, and put rubber stoppers in both ends as it’s pulled out.
These cores were our most common samples. In places where the mat was thin and had coarse sand or gravel below it, the cores didn’t work. For these samples, the diver would use the core tube to cut through a section of mat and then waft the mat into the core tube sideways. For very thin samples, Ian used a small Nalgene bottle with the bottom cut off to cut through the mat, and he put the cutouts into boxes.
Dale also did a couple of dives where he swam instruments around under water to map out variations in light and chemistry. These sorts of dives are ones that require a lot of note taking because approximate locations and sometimes instrument values have to be recorded. We used the time of observations to provide data to correlate to chemistry measured by the instrument. We haven’t gone through these notes yet to see how well we did. That’s a job for the months between now and the next field season.
Ian ended his underwater time with an epic dive in which he did 3 dives worth of work in a bit less than an hour. We melted a second dive hole and decided to use it as a reference for changes over the next year.
Ian had put in a transect line the day before to mark a specific area that could be documented this year and again next year. It was held in place by bamboo stakes and had floats to keep the line off the lake floor. Ian started the epic dive by adjusting the line, placing the floats in good places, putting in a bamboo stake that had come out, and pounding in the end stakes with a hammer. (Think about how hard it would be to pound something into sandy ground underwater. With nothing much to push against, conservation of angular momentum causes some difficulties we don’t have on land.) Ian then swapped the hammer for a camera and photographed each of the areas with either a meter mark on the line or a bamboo stake in the lake floor.
After that, he deployed 6 sediment traps to see how much sediment settles out in the next year. This was a lot of work. I could tell it was hard as I tended the dive line. Ian was constantly moving back and forth, up and down. And he wasn’t talking. I paid very close attention to the tension on the line, trying to keep it exactly right so it wouldn’t interfere with his work. Luckily, it was a beautiful day with little wind, so it was very pleasant to be standing on the ice, and it was easy to concentrate.
Me, wearing only a few layers!
The diving was very challenging. First, the divers are under the ice with only one way to the surface. They have to always keep that in mind. Second, they are wearing full face masks with a tether to the surface. The face masks restrict visibility to only straight ahead.
Dale getting help from Bekah with his mask just before a dive.
The tether (or air and communication line) can get tangled around things, can get in the way, and if it’s too tight, can pull the diver. Third, the water is just about 0°C. It’s cold, even with a good, insulating dry suit on.
Ian and Dale chipping ice out of the dive hole so they can get through. Early in the season, 10 cm or thicker ice would form over night. Later, it warmed up, and only a thin layer was present.
Ian in his dry suit getting ready to dive.
Fourth, the divers can’t touch the bottom of the lake without stirring up mud that clouds the water. They try to touch the bottom as little as possible. Fifth, the work requires very careful buoyancy control. The divers are weighted with lead weights to help them sink, and they add air to their dry suits to help them float. Work near the bottom without touching it requires that the divers perfectly balance the amount of air they have in their suits. The air compresses when they go deeper because the pressure is greater (PV = nRT so if P (pressure) increases, V (volume) has to decrease because the number of air molecules (n) and temperature (T) stay the same; R is a constant). To increase the volume to help them float, the divers add air, e.g. they increase n. However, if they go shallower in the water and n is still high, they keep going up faster and faster. Thus, the divers have to let air out of their suits. Doing this precisely is an important skill, particularly since there is one more complication: breathing! Breathing in has a similar effect to putting air into the suit, and breathing out does the opposite. Thus, divers tend to move up in the water when they breath in and down when they breath out. Often when Ian or Dale was doing something delicate, they would hold their breath, sometimes taking in a bit more or letting some out to get their position in the water exactly right.
Sixth, some jobs required several instruments and tools. Some of these float and some sink. Keeping all of them under control when you can’t necessarily set them down and have them stay put is a challenge in itself.
Seventh... I think you get the point. I’m in awe of how much Ian and Dale got done under water!
