Alaska Collaboration, Ongoing and Future Projects

gwiles August 13, 2023 10:07 pm

In addition to the summer work described by Lilly Hinkley and Tyrell Cooper, the Wooster Tree Ring Lab is collaborating projects with (1) The Tree Ring Lab of the Johannes Gutenberg-University in Mainz, Germany. This work is part of a project called Monostar (Modelling Non-Stationary Tree growth Responses to global warming) and (2) The University of Alaska – Fairbanks funded by the National Science Foundation, which involves developing long tree-ring records from along the Gulf of Alaska. This post describes some of the sampling aspects of these projects this past summer.

First MONOSTAR sampling: We started in Juneau – here (below, left to right) is Nick Wiesenberg (Wooster), Philipp Romer (Mainz), and Davide Frigo (University of Padova, Italy).

The first tree-ring site was above the Mendenhall Glacier at the East Glacier Site. MONOSTAR sampling is being done across the Northern Hemisphere to determine the whys, hows, wheres and whens of changing tree growth with changing climate. The trees in the background are mountain hemlock with a few Sitka spruce. This is close to a yellow cedar site that we sampled some years ago.

Philipp and Davide with Mendenhall Glacier in the background. 

The next stop was Glacier Bay where we flew to Gustavus. The Tlingit Meeting House in Glacier Bay. The totems here in Bartlett Cove look to the east towards Excursion Ridge where the team sampled an Alaska Yellow Cedar and a Shore Pine tree-ring site.  

Walking up Excursion Ridge – the first obstacle was a river crossing a bit deeper that our boots, Nick manufactured a bridge for the group.

Philippe shows off a large diameter tree core from an Alaska Yellow Cedar core. After the work with MONOSTAR, we left Bartlett Cove and caught a ride with the Foglark Research Vessel with captain Justin Smith who brought us to the East Arm of Glacier Bay (Muir Inlet).

The Foglark sits offshore after dropping us off with our kayak in Muir Inlet. The mission was to sample wood in fans along the margin of the fiord in the wake of the retreating ice. The priority was to sample wood in the 2000 year old range. 

Most of the area we explored over a 9-day period was covered in ice very recently. The map above shows location at the head of Muir Inlet south to McBride Glacier. 

In the summer 2023 Muir Glacier (right) is now split into Muir and Morse Glacier (left), which are both terminating on land now, rather than in the ocean (tidewater glaciers).


Landing at the head of Muir Inlet we examined the outwash of the considerable rivers flowing, but no wood was found.

Nick shown scouring the many tributary side valleys that are recently deglaciated – many that were sampled successfully for wood in years past have been scoured of wood, likely due to large rainstorms and mass movements.

The next stop was McBride Glacier. Recent (last 5 years) ice retreat has opened up new landscapes and the potential of buried wood. We know from previous sampling that the wood should be in the 8,000 year old range. 

The view into McBride is spectacular. 

2020 GoogleEarth image above shows the tidewater McBride Glacier and the 2023 ice margin. 

August 2023 ice margin on this GoogleEarth image. The tributary valleys just south of the ice margin have been exposed over the past two years.

To the left and the right of the 2023 ice margin, the two valleys recently exposed by the retreating ice. The valleys align along a fault zone.

Nick is standing on a major sand bar/ delta in the middle of the fiord suggesting the glacier may be grounded now, or is there ice below the sand? It is hard to determine. It may be with the large sediment wedge the glacier will slow its retreat or even advance a bit.

From the mid-fiord sand bar looking downfjord – the two deltas to the left and right are contributing large volumes of sediment to the fan we are standing on.


Nick samples the 8000 year old wood encased in ice-marginal sediments.

An 8000 year old Sitka spruce stump in place – it is reminiscent of a totem.

The North Pacific pours in and out of McBride Inlet twice a day – the navigation is tricky. We look forward to further work on McBride.


The next stop down Muir Inlet was in the shadow of the Nunatak – the wood here is in the critical 2000 year old range (run over by ice 2000 years ago). A Nunatak is a hill/mountain surrounded by ice (from Inuit nunataq).

Nick shows the haul of wood sampled from drainages around the Nunatak. 

The final sampling in Muir Inlet was done as we paddled south down Muir Inlet. Here we camped with a spectacular view of Mt. Wright. From previous work we have amazing Mt. Hemlock data from this impressive mountain. 


Along the way, Nick stops at a log that we know is about 4000 years old. It may not look like a log but it is a Mt. Hemlock tree with well over 350 rings. We know this as we sampled it last year 2022.

Nick extracts the section.

A panorama of McBride Fiord (right) and Muir Inlet (left) during a flooding tide. We thank The College of Wooster, the National Park Service, the National Science Foundation, and all the students and collaborators who have contributed to this work. 

 

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Coring Trees and Flying over Seas, Hoonah, Alaska 2023

gwiles July 18, 2023 3:41 pm

Guest Bloggers: Lilly Hinkley and Tyrell Cooper

Tyrell, Lilly, Nick and Dr. Wiles of Wooster’s Tree Ring Lab (WTRL) were in Juneau and Hoonah, Alaska working in collaboration with the Alaskan Youth Stewards (AYS) in order to extend our tree ring chronologies. Once we collect the tree cores, the WTRL group will head back to The College of Wooster to prep and measure the cores and do a climatic analysis on them to try and connect the data with some of the Tlingit oral histories we learned about during our time. 

Nick, Tyrell and Lilly at the Mendenhall Glacier ice margin.

Day 1

Tyrell and Lilly safely landed in Juneau. We fueled up and then went on a short walk around Mendenhall Glacier Lake where we saw a triple sun dog – a sign of good luck as we embarked on our journey in Alaska.

We met up with a fellow dendrochronologist, Markus Stoffel (left), along with his family who are from Switzerland. We also met up with another colleague, Ben Gaglioti (second from left) who works as a researcher at University of Alaska Fairbanks. Ben joined us while we were in Hoonah as well.

 

Lilly and Tyrell in front of Nugget Falls. Which pours from a surrounding glacier into Mendenhall Lake.

Day 2

On day 2, The Wooster Tree Ring Lab (WTRL) crew started off the day with a hike on the West Glacier Loop trail.

Took a quick peanut butter and jelly lunch break with a great view of the glacier.

After a long journey we made it to the glacier’s terminus, and walked down into an ice cave beneath a moulin.

Day 3 

 

On day 3, we headed out on Alaska Seaplanes from Juneau to Hoonah.

Aerial view from the flight to Hoonah.

Once getting into Hoonah, we took a drive around town with our friend Jeff, who gave us a brief history of Hoonah. We then took a quick hike at the Suntaheen trailhead to stretch our legs.

Later that night, Nick, Lilly and Tyrell went out to pick some wild blueberries and salmonberries.

 

Day 4

 

On day 4, w met up with the Alaskan Youth Stewards (AYS) crew and then began our arduous hike up Ear Mountain to look for some slow growth Mountain Hemlock trees to core.

Photo of the “ears” of Ear Mountain.

Lilly coring a Mountain Hemlock.

 

Day 5

 

On day 5, we began the day by coring Yellow Cedar.

The AYS group had gone out on a boat earlier to catch Bull Kelp, Halibut and Dungeness crab. We met up with them at the harbor where they showed us how to filet halibut.

Photo of Bull Kelp.

We later helped them prep the Bull Kelp for pickling.

To end the day, we went to the beach to pick some beach asparagus.

 

Day 6

 

On day 6, we met with the AYS crew in the morning to show them the process of mounting, sanding and counting the tree cores.

After a quick lunch break, we learned how to pickle the Bull Kelp using a brine mixture and put them into jars.

 

Day 7

On day 7, after flying back to Juneau from Hoonah, Dr. Wiles, Lilly, and Tyrell visited the State Museum. We learned more about Alaska’s native population. Photo includes Woolly Mammoth tusks.

Exhibit of seal intestine raincoats that Alaskan natives would wear.

Exhibit of a large cross-section of old-growth Western Hemlock. This tree was commonly logged.

 

Day 8

Last photo in front of the Mendenhall Glacier before heading back to Wooster.

To learn more about the AYS group click here

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Aquatic siliceous microbiota team excelling with summer research at The College of Wooster

Mark Wilson July 6, 2023 1:23 pm

I am honored to be working with a great research team this summer in Scovel Hall at The College of Wooster. Our topic has been the analysis of the siliceous sponges and diatoms in a sediment core from Brown’s Lake near Shreve, Wayne County, Ohio. Above are Minnie Pozefsky on the left and Garrett Robertson on the right conferring on Garrett’s magnificent chalkboard notes. (Yes, there are more sliding boards filled with text behind these.) Minnie, soon to be an entering student at Williams College, is our diatom expert; Garrett is a rising senior at Wooster and our sponge person. This work is part of Garrett’s Senior Independent study project.

Brown’s Lake is well known to Wooster Earth Scientists and readers of this blog. Dr. Greg Wiles started a series of projects in this lake and bog system many years ago, and hundreds of Wooster students have visited it on class field trips and for research at many levels. This is a kettle lake formed at the end of the last Ice Age when a huge block of ice (“dead ice”) was left at the margin of the retreating continental glacier. That melting ice block was surrounded by glacial sediments and eventually became a lake. This means the sediment in the lake goes back at least 11,000 years to the retreat of the last glaciers in this part of the world.

We have access to a beautiful core taken from the center of the lake by our colleagues at the University of Cincinnati. (We share an NSF grant with them for this work.) This core is 1.5 m long and extends from the very recent at the top to probably the 16th century at the bottom. (We are awaiting radiometric dates for a better age estimate.) The core is laminated, meaning the sediment accumulated in undisturbed layers, year after year. This is critical for our analysis of each layer because their relative ages are retained. The core is mostly peat in the bottom 75 cm or so, and then a silty layer begins to appear above. This represents the anthropological effect of European-American settlement of the area in the early 19th century. Our research objective is to describe the paleoenvironments recorded sequentially through this core using the skeletons of diatoms and sponges entombed in the sediment. We already see the dramatic effects of clearing and farming the land. We hope to go back further to see if we can detect climate changes prior to European settlement.

Minnie is spending a lot of time at this photomicroscope identifying, counting, and recording diatoms in smear slides made every 5 cm from the core sediment.

This is a typical microscope view for Minnie this summer. The fish-like form and two circles above the scale bar are diatom frustules (the name for their skeletons). Diatoms are single-celled algae with siliceous skeletons. They are incredibly diverse in most aquatic systems. They are photosynthetic and may produce up to a third of atmospheric oxygen. Most important for us, their frustules are easily preserved, and their taxonomy and abundance can be used as proxies for changing environmental conditions.

Our diatom pioneering forebear Justine Paul Berina (’22) made this beautiful image of the diatom Pinnularia during his Independent Study project. He and Richard Torres (’23) developed many of the lab techniques we’re using this summer.

Garrett Robertson (’24) is here in one of our Scovel labs preparing slides of sponge spicules and diatoms by essentially removing most of the organic materials from the core sediments. It involves hot hydrogen peroxide and centrifuges.

The spiky object at the top of this image is a sponge spicule (with a diatom beneath it). The sponge spicules we have are, like the diatoms, made of resistant silica. In life they formed the internal skeletons of sponges. Like our own bones, a single sponge has many different sizes and shapes of spicules.

This is another sponge spicule, an image taken two years ago by Justine Paul Berina.

The 2023 aquatic siliceous microbiota team! We occasionally get chances to leave the lab. Here we are in the woods near Brown’s Lake and Brown’s Lake Bog. (Picture taken by my brother Wynn Wilson.) Minnie and Garrett were assisting this year’s AMRE Team as they extracted cores from trees.

So far we have found very interesting patterns in the distribution of sponge spicules and diatoms in the Brown’s Lake core. The ecological collapse associated with forest clearing and drainage from new farms is obvious. We think that we also have a record of a possible cooling event in the 17th century, but we have much more work to nail that hypothesis down.

This has been great fun. As always, I have learned much from our work.

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Another new paper: A nestling brachiopod in an Ordovician boring and its implications

Mark Wilson June 8, 2023 9:54 am

I know, I know, several new papers lately. This spike in publications is a function of two things: The pandemic with its enforced isolation meant my colleagues and I had more time to finish manuscripts, and I belong to some wonderful networks of very productive scientists. This has all been highly collaborative.

This new paper (a cover story) in Palaios describes a tiny lingulid brachiopod found inside a boring drilled into an internal mold (steinkern) in the Middle Ordovician of Estonia. (Now this is esoteric paleontology!) The abstract —

ABSTRACT: A steinkern of an endoceratid nautiloid siphuncle [see top image] contains a Trypanites sozialis boring with a lingulate brachiopod Rowellella sp. shell inside. The steinkern of this endoceratid formed during early lithification of the sediment on the seafloor. The lithified steinkern of this siphuncle was either initially partially exposed to the seawater or was exhumed and stayed exposed on the seafloor, where it was colonized by boring organisms. This bioerosion resulted in numerous Trypanites borings in the siphuncle. After the death or exit of the Trypanites trace maker, a vacant boring was colonized by a small lingulate nestler Rowellella sp. This lingulate was likely preadapted to life in hard substrate borings when it first found its way into borings in living substrates in the Late Ordovician. The increased availability of hard substrate borings, combined with the increased predation pressure due to the GOBE, enhanced the colonization of hard substrate borings by lingulate brachiopods.

Trypanites sozialis Eisenack, 1934 (Tr) in steinkern of cephalopod from the Kunda Regional Stage, Kunda-Aru quarry (GIT 426-674-1).

Lingulate Rowellella sp.in Trypanites sozialis boring from Uuga cliff, Lasnamägi Regional Stage (Darriwilian), NW Estonia (TUG 1393-186).

That you to Olev Vinn and my other Swedish and Estonian colleagues!

Reference:

Vinn, O., Holmer, L.E., Wilson, M.A., Isakar, M., and Toom, U. 2023. A Rowellella (Lingulata, Brachiopoda) nestler in a Trypanites boring from the Middle Ordovician of Estonia: An early colonizer of hard substrate borings. Palaios 38: 240-245.

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The Ordovician Bioclaustration Revolution: A new paper

Mark Wilson June 6, 2023 8:08 am

Bioclaustration is the process by which an organism is embedded within the growing skeleton of another. Bioclaustrations are fascinating in the fossil record because they give direct information about how two or more organisms lived together in the ancient past — a form of symbiosis. My Estonian and German colleagues have just published a paper in the journal Geobios on the rapid burst of bioclaustrations in the Late Ordovician. The senior author is the indefatigable Olev Vinn. The abstract tells the story —

ABSTRACT: There was a sudden increase in the diversity of bioclaustrations in the Sandbian (Late Ordovician) that continued somewhat more slowly in the Katian. The Sandbian was also the time when bioclaustrations became common, at least in Baltica. The major increase in the diversity of bioclaustrations in the Late Ordovician was an outcome of the GOBE [Great Ordovician Biodiversification Event], and we term it the Ordovician Bioclaustration Revolution. The Ordovician Bioerosion Revolution may partially be responsible for the beginning of the Ordovician Bioclaustration Revolution in the Sandbian, as a number of these early bioclaustrations started their growth from initial borings. The diversification of bioclaustrations in the Sandbian involves mostly bryozoans and, to a lesser extent, brachiopods as hosts. The Katian increase in bioclaustration diversity involves mostly corals as the hosts and was likely unrelated or at least less influenced by the Ordovician Bioerosion Revolution. A new broadly conical bioclaustration, Kuckerichnus kirsimaei nov. cgen., nov. csp., is here described from the growth surfaces of hemispherical trepostome bryozoan colonies of Diplotrypa bicornis, Mesotrypa orientalis and Mesotrypa excentrica from the early Sandbian (Late Ordovician) of Estonia.

The top image is from Figure 2 in the paper. The caption: Holotype GIT 343-45-2 of Kuckerichnus kirsimaei nov. cgen., nov. csp. in Diplotrypa bicornis from the Küttejõu opencast mine, Kukruse Regional Stage. B. Paratype GIT 343-45-4 of Kuckerichnus kirsimaei nov. cgen., nov. csp. in Diplotrypa bicornis from the Küttejõu opencast mine, Kukruse Regional Stage. C. Paratype GIT 343-45-5 of Kuckerichnus kirsimaei nov. cgen., nov. csp. in Diplotrypa bicornis from the Küttejõu opencast mine, Kukruse Regional Stage. D. Paratype GIT 343-48-1 of Kuckerichnus kirsimaei nov. cgen., nov. csp. in Mesotrypa orientalis from the Küttejõu opencast mine, Kukruse Regional Stage. Scale bars: 1 mm.

I enjoyed this project very much because it summarizes decades of work going back to when my friend Tim Palmer and I were working together for the first time in the 1980s. It is nice to see so many concepts and observations coming together into coherent, testable evolutionary hypotheses.

Reference:

Vinn, O., Wilson, M.A., Ernst, A. and Toom, U. 2023. The Ordovician bioclaustration revolution. Geobios (https://doi.org/10.1016/j.geobios.2022.10.007) [Link goes to free pdf until July 25, 2023.]

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A new paper on brachiopod symbiosis in the Early Paleozoic

Mark Wilson May 20, 2023 1:19 pm

My Estonian colleague and friend Olev Vinn and I have been working for many years on examples of parasitism recorded in the fossil record. For the last couple of years we have been summarizing the data and assessing paleoecological and evolutionary patterns through the Phanerozoic. One of our review papers was published today in the journal Historical Biology. Lars Holmer, an expert on brachiopods from Uppsala University in Sweden, joined the team for this work. Here is the abstract —

The evolution of brachiopod symbiosis is closely tied to the evolution of brachiopod faunas and their partner groups during the early Palaeozoic. Brachiopod groups with a larger number of taxa had more symbiotic associations, and there was no specific group that was more prone to symbiosis during this time interval. The first symbiotic associations appeared soon after the emergence of certain brachiopod groups, with Cambrian brachiopods partnering with typical representatives of the Cambrian fauna. Bryozoans and tentaculitoid tubeworms, which became important partners during the Ordovician and Silurian, first diversified in the Ordovician. The gradual decrease in the number of brachiopod partner groups from the Cambrian to the Silurian was likely due to specialisation. However, the number of symbiotic associations did not increase faster than the number of brachiopod taxa. The GOBE-induced diversification of brachiopod taxa did not lead to an escalation in symbiotic relationships. Symbiotic associations involving brachiopods continued after the end-Ordovician mass extinction. Although early Palaeozoic brachiopods were vulnerable to kleptoparasites, the harm caused by these parasites was not enough to drive their associated brachiopods to extinction.

The caption for the top image from the paper: Figure 1. (A) Burrinjuckia clitambonitofilia bioclaustration in the rhynchonelliform brachiopod Clitmabonites squamatus from the Sandbian of NE Estonia (GIT 343–236).

As always, I learned a great deal from my colleagues on this project.

Reference:

Vinn, O., Holmer, L.E. and Wilson, M.A. 2023. Evolution of brachiopod symbiosis in the early Paleozoic. Historical Biology (https://doi.org/10.1080/08912963.2023.2212368)

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Consequences of publishing fraud: A geosciences journal placed on probation

Mark Wilson May 15, 2023 8:41 am

In the Fall of 2021, in the depths of the covid pandemic, I found a long series of fake papers in the Springer Nature Arabian Journal of Geosciences. These were blatant frauds, with nonsense titles, nonsense references, and nonsense text in between. I reported these papers to the editors and then posted a description on the anonymous publishing watchdog site PubPeer. Internet sleuths then found many more fake papers in this journal. The story made it to the front page of The Chronicle of Higher Education, and eventually to the journal Nature. This history is detailed in a previous post.

Now, after hundreds of paper retractions by Springer Nature, the Arabian Journal of Geosciences has been placed in a kind of probation (see above screenshot). Clarivate Analytics has removed the journal’s listing from Web of Science for at least 2 years. The indexing service Scopus has at least temporarily dropped the journal.

Scientific publishing is experiencing a growing flood of fake papers produced by lucrative “paper mills” that sell manuscripts to would-be authors and then take advantage of corrupt and inept editorial systems to get them published. The common practice of Article Processing Charges (APCs), by which authors pay to have their papers published, has greatly accelerated the fraud. Journal editorial boards are often more interested in receiving the fees than ensuring quality in the published papers. We need a new model for ensuring the integrity of scientific publication — a model that encourages honest peer review and editorial gatekeeping. Without a change, confusion and mistrust will tear at the fabric of scientific research and its countless contributions.

I keep track of these issues through the blogs For Better Science and Retraction Watch.

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An Analysis of the Effects of Water Chemistry on Diatom Ecology Over Time in the American Upper Midwest — The Independent Study project of Richard Torres (’23)

Mark Wilson May 9, 2023 10:45 am

Editor’s Note: Independent Study (IS) at The College of Wooster is a three-course series required of every student before graduation. Earth Sciences students typically begin in the second semester of their junior years with project identification, literature review, and a thesis essentially setting out the hypotheses and parameters of the work. Most students do fieldwork or lab work to collect data, and then spend their senior years finishing extensive Senior I.S. theses. Richard Torres was advised by Mark Wilson (me!). The following is his thesis abstract —

In this study, I investigated changes in diatom population composition in relation to water chemistry in North American Upper Midwest lakes over the past three decades. I collected diatom samples from several lakes (Ohio, Minnesota, Wisconsin, North and South Dakota) using sediment cores and sediment traps. I observed an increase in the average diversity of diatoms over the three decades, but no significant similarity between the diversities of the lakes. I calculated the dissimilarity of the populations through Bray-Curtis Dissimilarity, finding it to be moderate to high between the lakes through time, with an average dissimilarity of 70 percent, which indicates a high difference between the population makeups between the lakes, past and present.

To analyze how diatom assemblages shifted regarding changes in water chemistry and other environmental factors, I used both bivariate correlation on diversity and general linear models with repeated measures on diatom population composition. From this analysis, I found that pH has a stronger effect and specific conductivity has a weaker effect on diatom diversity when compared to three decades ago. On individual genera, pH and water clarity did not have a significant effect on diatom assemblages, while total dissolved solids did. Moreover, individual genera were less influenced by specific conductivity than they were three decades ago. When analyzing modern diatom assemblages in relation to water chemistry, I found that pH, oxidation-reduction potential, specific conductivity, salinity, total dissolved solids, and water density all had significant effects.

There were potential difficulties and sources of error in this study. For instance, I used a smaller number of diatoms than recommended in other studies, and there were difficulties in identifying certain genera. Survivor bias was also possible, where the diatoms studied might not be representative of the lakes’ populations as some might have been destroyed between life and being mounted on the slide, by predation, silica dissolution, and fragmentation during centrifuging, among other hazards. This study holds implications for lacustrine resource management and climate reconstruction, as there is little to no research regarding changes to diatom ecology in the American Midwest in the past 20 years, furthermore, no research has been done looking at the effects of water density on diatoms. Further research is needed to better understand diatom’s complex interactions with their environment.

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The Gunlock Member: Description of a Proposed New Member of the Carmel Formation (Middle Jurassic) of Southwestern Utah — The Independent Study project of Lucie Fiala (’23)

Mark Wilson May 8, 2023 10:56 am

Editor’s Note: Independent Study (IS) at The College of Wooster is a three-course series required of every student before graduation. Earth Sciences students typically begin in the second semester of their junior years with project identification, literature review, and a thesis essentially setting out the hypotheses and parameters of the work. Most students do fieldwork or lab work to collect data, and then spend their senior years finishing extensive Senior I.S. theses. Lucie Fiala was advised by Mark Wilson (me!) and was on Team Utah 2022. The following is her thesis abstract —

This Independent Study investigates the paleoecology and stratigraphy of the lower Carmel Formation in southwestern Utah. The Co-op Creek Member and the here proposed Gunlock Member of the Carmel Formation are mostly limestone units formed during the Bajocian (Middle Jurassic). During the Middle Jurassic, much of western North America was covered by an epicontinental seaway called the Sundance Sea, which stretched from southern British Colombia to Utah. In this study there are four principle locations (Eagle Mountain Ranch, Manganese Wash, Dammeron Valley, and Jackson Peak) of study. The proposed Gunlock Member was formed in a low energy, intertidal environment. It is characterized by stromatolite and thrombolite layers, trace fossils, and bivalves. The overlying Co-op Creek Member was formed after a transgression in a high energy, subtidal environment and is characterized by its ooid-rich limestones, shales, and abundant fossils.

The boundary between the Co-op Creek and proposed Gunlock divides these members into the underlying stromatolitic member and the overlying ooid-rich member, and indicates a significant transgression. The Bajocian saw a few notable global transgressions that roughly coincide with that of the Sundance Sea; while there are several theories as to the cause of these rises in sea level, tectonic and glacial activity are the most likely.

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The Nuclear Densitometer: Its Design, Use in Construction, and an Experimental Application — The Independent Study project of Addie Tagg (’23)

Mark Wilson May 7, 2023 10:34 am

Editor’s Note: Independent Study (IS) at The College of Wooster is a three-course series required of every student before graduation. Earth Sciences students typically begin in the second semester of their junior years with project identification, literature review, and a thesis essentially setting out the hypotheses and parameters of the work. Most students do fieldwork or lab work to collect data, and then spend their senior years finishing extensive Senior I.S. theses. Addie Tagg was advised by Mark Wilson (me!). The following is her thesis abstract —

The nuclear densitometer, or nuclear gauge, is a tool that is used to take the most accurate measurements of density and moisture content in soils, aggregates, and other materials. These measurements are used for many aspects of construction. The gauge takes density measurements based on the radioactive source Cesium-137. Key concepts for understanding how the gauge operates include photoelectric absorption, Compton scattering, and pair production. It is impossible to measure the reaction of a beam through a material, but it is possible to calculate the percentage of a source that is absorbed. The source that is not absorbed is reflected. The denser that a soil is, fewer waves are detected. After the device is calibrated and the number of reflected particles is counted, this number can then be translated into wet density. Alternative methods of recording density include the dynamic cone penetrometer and sand replacement. Overall, the nuclear densitometer is the easiest and least destructive method of density testing. The gauge does not directly measure water content, but instead measures hydrogen. This fact led me to an experiment to inquire if a common household weed killer would affect the gauge’s ability to take accurate measurements. The experiment included three trials using two layers of crushed limestone, each with a different substance applied (dry stone, water, or weed killer), compacted with a hand tamper and measured for compaction with the nuclear gauge. Overall, the weed killer did not affect the gauge’s ability to take an accurate measurement.

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