Lake Joyce - It isn't what we expected
Written October 28, 2009
[We have web access, at least for now! I'll add photos later if the connectivity remains.]
Lake Joyce... It isn’t what we expected.
In any field science project, you choose a place to go and things to do before you’ve been there and done them. You use all the data you can find to choose the best place, to make predictions about what you’ll find, and decide what work to promise to do in your grant proposals. When you get there, you find unexpected things. Sometimes you can’t even do the science you proposed. It gets exciting and challenging. It always happens to at least some degree. On this trip, we got a big, unexpected surprise.
We melted a dive hole through the ice.
The ice was thinner than it was when Dale was here before - only a bit less than 5 meters thick, although it is 6 meters thick in the middle of the lake.
The first dive down found sediment coating all the microbial mats we’ve come here to study. The mats are barely alive. We only found a few living cyanobacterial filaments in samples brought to the surface. Life in Lake Joyce has been tough lately. We won’t be able to do a bunch of the research we proposed. But we are here, and things are interesting. How do we reshape our science plans?
Today, on dive 5, Ian took down an instrument (a PAM Fluorometer) that measures how much chlorophyll is present in a small area of mat as well as whether it is attached to energy-producing biosynthetic pathways; in other words, it tells you whether photosynthesis can produce energy for the bacteria in the mat. Almost all the mats below 16 meters water depth show very little photosynthetic activity. At about 16 meters, as well as shallower, there are patches of mat that weren’t as buried by sediment. These areas show more reasonable photosynthetic activities, but they are still very low compared to other lakes in the area. Unexpectedly low.
Why?
We hypothesize that the microbial mats are barely getting enough light to live. Based on the large amount of very fine sediment on top of the mats, they may have been partially killed by sediment blocking their light. We’ll compare ones with more and less sediment to test this idea. Also, there is a lot of very very fine “rock flour” floating in the upper part of the lake. Rock flour consists of tiny bits of rock that are ground up as glaciers move. It floats for a long time because the grains are so small and the upper part of the lake is convecting (the same process I described before that moves heat) which keeps carrying the particles upward. The rock flour scatters light, which means that the mats at the bottom of the lake get even less light than they would if the water was clear. Thus, we think that sedimentation has disrupted mat growth, and we’ll try to test this idea.
So this is where we are: We came here to learn how the mats make peaked structures and ridges, but if they are mostly dead, we can’t do experiments with them that we planned. Rather, we have to come up with new questions, ones we can answer. Here are some of our new ideas:
1) There was a big influx of sediment some time between when Dale was here in 1997 and now. When did it occur? Is it associated with a lake level change observed elsewhere in the Dry Valleys? How much sediment was brought in to the lake? Where did it come from? Is the sediment spread across the entire lake or are there some areas that still have active microbial mats? We’ve only looked in one area. It isn’t one that appears to have a particularly large supply of sediment based on the geomorphology of this part of the lake. Our suspicion is that the whole lake had a large sedimentation event. How do we test this?
2) How can we determine how much the level of Lake Joyce has changed?
Alfonso and I mapped the shoreline with GPS yesterday by walking around it. Today, I looked a photo Dale sent me from last time he was here. The shoreline is definitely higher. Thus, we’ve convinced ourselves that the lake level has gone up, but how can we make some good quantitative measurements? There are some deltas going into the lake. Their geometry suggests there was flow down the gullies that feed them while the lake was close to it’s current depth. Other flows don’t show delta-like geometries now. I suspect that these probably haven’t flowed since the lake level rose; their deltas are now under the ice. How can we tell when the flows occurred? That could tell us when lake level rose.
3) How have combined changes in lake level and sedimentation affected the microbial mats? How long have the microbial communities been stressed by these changes? How long will it take them to recover? What does “recovery” involved? Based on observations of other Dry Valley lakes, Ian thinks that it takes years, maybe a decade, for the mats to build up again. What observations do we need to make now and in the future to understand the “recovery” processes?
4) Are there areas of mat or areas in the lake where we can do some of the research we planned? Specifically, are there areas where the microbial activity is high enough that it is worth measuring chemical gradients to look for microbial influences on lake chemistry? Also, there are structures that are mineralized by calcite. Have these changed? Can we see these changes in the composition or color of the minerals? Finally, are there any bacteria that are doing well enough that we can study their motility and pattern formation behaviors?
There are still some really interesting things that we proposed to do and can still do. Some morphology of the mats are still the same, and they are very much like the ancient microbial structures I’ve studied in the rock record. We can make some nice morphological comparisons. Also, some of the microbial structures were coated in calcite. We can still look for microbial influences on the calcite formation as well as image any laminae, etc. inside the calcified structures. We may very well find a sample or two of active bacteria we can study for microbial motility. It’s all hard to predict at this point.
And it is really beautiful here!
[We have web access, at least for now! I'll add photos later if the connectivity remains.]
Lake Joyce... It isn’t what we expected.
In any field science project, you choose a place to go and things to do before you’ve been there and done them. You use all the data you can find to choose the best place, to make predictions about what you’ll find, and decide what work to promise to do in your grant proposals. When you get there, you find unexpected things. Sometimes you can’t even do the science you proposed. It gets exciting and challenging. It always happens to at least some degree. On this trip, we got a big, unexpected surprise.
We melted a dive hole through the ice.
The ice was thinner than it was when Dale was here before - only a bit less than 5 meters thick, although it is 6 meters thick in the middle of the lake.
The first dive down found sediment coating all the microbial mats we’ve come here to study. The mats are barely alive. We only found a few living cyanobacterial filaments in samples brought to the surface. Life in Lake Joyce has been tough lately. We won’t be able to do a bunch of the research we proposed. But we are here, and things are interesting. How do we reshape our science plans?
Today, on dive 5, Ian took down an instrument (a PAM Fluorometer) that measures how much chlorophyll is present in a small area of mat as well as whether it is attached to energy-producing biosynthetic pathways; in other words, it tells you whether photosynthesis can produce energy for the bacteria in the mat. Almost all the mats below 16 meters water depth show very little photosynthetic activity. At about 16 meters, as well as shallower, there are patches of mat that weren’t as buried by sediment. These areas show more reasonable photosynthetic activities, but they are still very low compared to other lakes in the area. Unexpectedly low.
Why?
We hypothesize that the microbial mats are barely getting enough light to live. Based on the large amount of very fine sediment on top of the mats, they may have been partially killed by sediment blocking their light. We’ll compare ones with more and less sediment to test this idea. Also, there is a lot of very very fine “rock flour” floating in the upper part of the lake. Rock flour consists of tiny bits of rock that are ground up as glaciers move. It floats for a long time because the grains are so small and the upper part of the lake is convecting (the same process I described before that moves heat) which keeps carrying the particles upward. The rock flour scatters light, which means that the mats at the bottom of the lake get even less light than they would if the water was clear. Thus, we think that sedimentation has disrupted mat growth, and we’ll try to test this idea.
So this is where we are: We came here to learn how the mats make peaked structures and ridges, but if they are mostly dead, we can’t do experiments with them that we planned. Rather, we have to come up with new questions, ones we can answer. Here are some of our new ideas:
1) There was a big influx of sediment some time between when Dale was here in 1997 and now. When did it occur? Is it associated with a lake level change observed elsewhere in the Dry Valleys? How much sediment was brought in to the lake? Where did it come from? Is the sediment spread across the entire lake or are there some areas that still have active microbial mats? We’ve only looked in one area. It isn’t one that appears to have a particularly large supply of sediment based on the geomorphology of this part of the lake. Our suspicion is that the whole lake had a large sedimentation event. How do we test this?
2) How can we determine how much the level of Lake Joyce has changed?
Alfonso and I mapped the shoreline with GPS yesterday by walking around it. Today, I looked a photo Dale sent me from last time he was here. The shoreline is definitely higher. Thus, we’ve convinced ourselves that the lake level has gone up, but how can we make some good quantitative measurements? There are some deltas going into the lake. Their geometry suggests there was flow down the gullies that feed them while the lake was close to it’s current depth. Other flows don’t show delta-like geometries now. I suspect that these probably haven’t flowed since the lake level rose; their deltas are now under the ice. How can we tell when the flows occurred? That could tell us when lake level rose.
3) How have combined changes in lake level and sedimentation affected the microbial mats? How long have the microbial communities been stressed by these changes? How long will it take them to recover? What does “recovery” involved? Based on observations of other Dry Valley lakes, Ian thinks that it takes years, maybe a decade, for the mats to build up again. What observations do we need to make now and in the future to understand the “recovery” processes?
4) Are there areas of mat or areas in the lake where we can do some of the research we planned? Specifically, are there areas where the microbial activity is high enough that it is worth measuring chemical gradients to look for microbial influences on lake chemistry? Also, there are structures that are mineralized by calcite. Have these changed? Can we see these changes in the composition or color of the minerals? Finally, are there any bacteria that are doing well enough that we can study their motility and pattern formation behaviors?
There are still some really interesting things that we proposed to do and can still do. Some morphology of the mats are still the same, and they are very much like the ancient microbial structures I’ve studied in the rock record. We can make some nice morphological comparisons. Also, some of the microbial structures were coated in calcite. We can still look for microbial influences on the calcite formation as well as image any laminae, etc. inside the calcified structures. We may very well find a sample or two of active bacteria we can study for microbial motility. It’s all hard to predict at this point.
And it is really beautiful here!
