This last week has been a hectic one in the Paleoenvironmental Lab.
Colton is back from his training at the Biosphere2, and Garrison is back in town from his stay at The National Center for Atmospheric Research. We are now operating at full capacity with two interns, one lab assistant, and two graduate students.
Grain Size Analysis
Colton has taken the lead on grain size analysis, and has spent the last five weeks preparing the sediments for the Auto Sampler by removing organic content, then removing biological silica.
We are interested in the grains of sediment that are washed in to the lake, but that signal can be muddled by the presence of organic materials (re: trees and leaves shed leaves and make "sediment" particles) and biological silica (small creatures called diatoms, live in lakes feeding on organic materials and other nutrients. When they die, they leave behind their tiny silica shells and deposit grains of biological silica). The size of the sediment grains tell us about how the sediments were deposited and can often be linked directly to heavy rainfall or drought events.
Loss on Ignition
Quite opposite of grain size analysis which requires us to eliminate organic components, we use Loss on Ignition, or LOI, to calculate total organic carbon as well as carbonate content of our sediments. Jared has become a professional at using the muffle furnace and has process over 300 samples in the last few weeks! We place the samples in muffle furnaces, and ignite the sediments at 500° C (this burns off all plant material) and then again at 1000°C (this combusts carbonate- inorganic carbon). The organic content of sediments is often used as an indicator of biological productivity within the lake and in the near by region. Pants grow, live, and decompose to make up the organic parts our sediment --- the rate of those biological processes is reflected in the amount of organic carbon in the sediment and responds directly to environmental conditions.
Charcoal Analysis
Both Kopo and Jared have been working on Charcoal this summer. The charcoal is pretreated with bleach and a dispersant to isolate charcoal particles from other organic materials and dark grains of sediment.
After the pretreatment step, we sieve the sediment to isolate particles that are greater than 250microns in diameter. This makes looking for charcoal easier as we filter out the clay and silt particles that could obscure our view of charcoal.
Finally, we use a stereo microscope at relatively low magnification (~50x) to identify and count macroscopic charcoal particles. For more on Charcoal check out Kopo's last blog.
μXRF
Kopo has turned wet sediments into hard slabs that can be used for thin section and X-ray derived elemental analysis. This process took WEEKS of coming in to the lab to check on the sediments, change out the resin fluid, and curing the sediment in an oven. The pucks were finally ready this week and Kopo learned how to use a diamond tipped band saw!
Data Interpretation
These proxies mean nothing if we don't interpret them. We collect thousands of individual data points to tell a story about our lakes and how they change over time. We perform statistical analysis to quantify measured changes and do our best to correlate our sediment record to observations of temperature, precipitation, stream flow, wind, ocean circulation, and a whole host of other contributors to local and global climate.
And just like that, another week of work has been completed here at the UA Paleoenvironmental lab.
We will continue to expand our toolkit for paleo-environmental reconstruction.
Until next time,
-Nicollette
Colton is back from his training at the Biosphere2, and Garrison is back in town from his stay at The National Center for Atmospheric Research. We are now operating at full capacity with two interns, one lab assistant, and two graduate students.
Grain Size Analysis
Colton has taken the lead on grain size analysis, and has spent the last five weeks preparing the sediments for the Auto Sampler by removing organic content, then removing biological silica.
 |
| Here are our grain size samples from Garrison's Nepalese lakes. They have been vigorously reacting with hydrogen peroxide (which removes organic content) for the last few weeks. This process is time consuming ---the samples react vigorously and can bubble over if we are not careful to measure how much chemicals we add and how long we let the samples sit in a heat bath. |
We are interested in the grains of sediment that are washed in to the lake, but that signal can be muddled by the presence of organic materials (re: trees and leaves shed leaves and make "sediment" particles) and biological silica (small creatures called diatoms, live in lakes feeding on organic materials and other nutrients. When they die, they leave behind their tiny silica shells and deposit grains of biological silica). The size of the sediment grains tell us about how the sediments were deposited and can often be linked directly to heavy rainfall or drought events.
 |
| An example of freshwater diatoms that can be mistaken for grains of sand. They are abundant in fresh and saltwater all around the world. They can also be studied in environmental analysis because many species re adapted to very specific environmental conditions. Diatom analysis is a rich discipline, but we do not use this approach in our lab. Photo Credit: Bill Daley |
Quite opposite of grain size analysis which requires us to eliminate organic components, we use Loss on Ignition, or LOI, to calculate total organic carbon as well as carbonate content of our sediments. Jared has become a professional at using the muffle furnace and has process over 300 samples in the last few weeks! We place the samples in muffle furnaces, and ignite the sediments at 500° C (this burns off all plant material) and then again at 1000°C (this combusts carbonate- inorganic carbon). The organic content of sediments is often used as an indicator of biological productivity within the lake and in the near by region. Pants grow, live, and decompose to make up the organic parts our sediment --- the rate of those biological processes is reflected in the amount of organic carbon in the sediment and responds directly to environmental conditions.
 |
| Here is our muffle furnace during the1000° C combustion. Thats about as hot as molten lava! |
Charcoal Analysis
Both Kopo and Jared have been working on Charcoal this summer. The charcoal is pretreated with bleach and a dispersant to isolate charcoal particles from other organic materials and dark grains of sediment.
 |
| Sediment sitting in pretreatment solution. |
After the pretreatment step, we sieve the sediment to isolate particles that are greater than 250microns in diameter. This makes looking for charcoal easier as we filter out the clay and silt particles that could obscure our view of charcoal.
Finally, we use a stereo microscope at relatively low magnification (~50x) to identify and count macroscopic charcoal particles. For more on Charcoal check out Kopo's last blog.
μXRF
Kopo has turned wet sediments into hard slabs that can be used for thin section and X-ray derived elemental analysis. This process took WEEKS of coming in to the lab to check on the sediments, change out the resin fluid, and curing the sediment in an oven. The pucks were finally ready this week and Kopo learned how to use a diamond tipped band saw!
 |
| Kopo in action: sawing the epoxy pucks in half to expose the fresh sediment surface. |
Data Interpretation
These proxies mean nothing if we don't interpret them. We collect thousands of individual data points to tell a story about our lakes and how they change over time. We perform statistical analysis to quantify measured changes and do our best to correlate our sediment record to observations of temperature, precipitation, stream flow, wind, ocean circulation, and a whole host of other contributors to local and global climate.
 |
| Notes from my last meeting with Kopo. Showing her the many factors that contribute to the deposition of laminations, variations in grainsize, organic carbon, and elemental concentrations that we interpret in this lab. Lots of squiggles and inputs. |
We will continue to expand our toolkit for paleo-environmental reconstruction.
Until next time,
-Nicollette
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