Tag Archives: krill
The gliders have been out on their own for more than a week. In that time they’ve traveled far out to sea, but today the team decided to turn one of them around and bring it almost all the way back home. Being close to shore is actually more dangerous for a glider than being in deep water, but they thought it would be worth the risk to meet up with the krill team’s echosounder and combine the two instruments’ strengths.
Click through the slideshow to learn about the glider’s travels—then check below for a quick look at what the two instruments found together:
This graph helps show how two instruments combine to create a better picture of what’s going on under the water’s surface. To read it, imagine that the glider is flying from left to right on the graph. As it moves slowly along this 1.5-mile track, it dives from the top of the graph to the bottom and measures chlorophyll levels. That gives an estimate of the amount of phytoplankton in the water, and phytoplankton are the main food of krill.
Now imagine the krill team driving their zodiac along the same route. The boat moves along the top of the graph (the surface of the water), and the echosounder detects patches of krill below it. Interestingly, the glider found a fairly high concentration of chlorophyll high in the water on the left side of the graph. The krill team found a patch of krill in deeper water beneath it, but not anywhere else.
“That’s pretty neat to find,” Dr. Kohut said, “that the only place on the whole transect there was krill was underneath the patch of chlorophyll.” The krill may have been resting during the day before swimming up to eat phytoplankton later in the day, Dr. Oliver said, or they may have been feeding on organic material as it drifted downward from the phytoplankton patch.
What’s really interesting about this find is that it couldn’t have happened without putting the two instruments—glider and echosounder—together. If the glider had been on its own, it would have noticed the phytoplankton, but we couldn’t have known whether krill were around to feed on it. On the other hand, if we’d had only the findings from the echosounder we’d have known there were krill around but we wouldn’t know why.
Today we went out to search for krill with Dr. Kim Bernard of Oregon State University and Shenandoah Raycroft, her assistant. Krill are an important stepping stone in Antarctic food chains because they eat tiny phytoplankton and then become food for almost all the large Antarctic animals including penguins, seals, and whales. Dr. Bernard and Raycroft use a machine called an echosounder to detect krill in the waters around Palmer Station.
Dr. Bernard set out to sample two areas based on tips she’d received from the radar team and the penguin team. The penguin team had noticed Adelie penguins were staying close to their colony on Torgersen Island, possibly meaning there were krill in those waters. The radar team had noticed an area of light currents near Cormorant Island that might also hold krill. This ability to quickly see data in the field and respond to what it’s telling them is called adaptive sampling, and it’s a major strength of the CONVERGE project.
Read through the slideshow to find out more about how Dr. Bernard’s team measures krill, and then check the bottom of the post to see some of their results:
After the team got back to Palmer Station they analyzed the data they had collected. The result was a plot like the one below that shows the readings that the echosounder recorded. The graph shows time on the horizontal axis and depth on the vertical axis.
To read the graph, you just have to imagine yourself in a boat sailing across the top of the image. The echosounder is sensing what’s beneath it—brighter colors mean the echo was louder, which means the object was more dense. That’s why the water appears white (no color) and the rocky seafloor appears red (the brightest color). Those two blue clouds are more dense than water and less dense than rock—they’re groups of krill.
Dr. Bernard analyzed the group on the right and found it contained about 180 pounds of krill stretched over an area 200 feet long and 20 feet high. At less than 0.04 ounces per krill that means, very roughly, there might have been 80,000 krill or more in that one group. Even so, Dr. Bernard said that today was a relatively slow day for a krill survey.
So what does a big krill day look like? When I asked Dr. Bernard this, she pulled up a graph from Dec. 23, 2011. Here it is:
You can read this graph just like the one above—look at the huge swath of greenish-blue covering most of the right half of the image above the seafloor! The greenish color is brighter than the blue, meaning that the krill are even more densely packed in these areas. And what about that circular white patch in the middle of the cloud of krill? Dr. Bernard said whales were swimming around the boat while they did this survey. She thinks that one had come through this spot with its mouth open just before the zodiac got there.
In the end, there weren’t large groups of krill near Torgersen or Cormorant Islands today. Dr. Bernard and Dr. Kohut think this may be because of the tidal currents that are happening during this part of the month. We’ll tell you more about that possibility in a post next week. Tomorrow, we’re going to go explore some penguin colonies.
Tuesday was a day off for the staff of Palmer Station. The day was sunny and calm—perfect conditions for a favorite off-duty pastime called recreational boating. We boarded a zodiac with station staff including the carpenter, logistics supervisor, satellite communications engineer, and utility mechanic. We loaded up with sunscreen, donned sunglasses against the brilliant white light, and pulled on orange float coats for safety. Everyone had a camera at the ready, and we set off to explore icebergs and islands.
For us it was a great introduction to the animal inhabitants of Palmer Station. We saw mammals, flying birds, flightless birds, and even a small but indispensable animal that keeps the whole ecosystem ticking. Can you guess what it was? Join us on our zodiac tour in the slideshow below, and find out the answer at the end:
Because krill are at the heart of the food chain, scientists pay a lot of attention to them. Krill are also at the center of Project CONVERGE. The team wants to know whether tides and convergence zones help bring together krill into concentrations high enough to serve as feeding hotspots for penguins. Radar helps the team map the currents and convergence zones. But how do they find out where the krill are? In our next post, we’ll go out with the scientists to answer that question.