Wooster Geologists

Guest Bloggers – SEAK25: On the third and final day in Angoon, we split into two groups. One climbed Hood Bay Mountain to extract high-elevation mountain hemlock cores, the other kayaked to Turn Point, searching for and coring culturally modified trees (CMTs). 

The CMTs at Turn Point are Sitka Spruce that have distinct scars with hack marks, evidence of previous Tlingit generations harvesting sap and fire starter. These CMTs are of heightened interest because a new hydroelectric power plant is soon to be built, and its road will require the removal of many trees in Turn Point. High school students in Angoon have already worked to preserve the CMTs by creating photogrammetric renderings. This work will prevent the information from there valuable trees, which connect locals to their lineage, from being lost altogether. We hoped to contribute to the effort by extracting cores to investigate their growth and date the scars using tree rings.

A map showing Turn Point in relation to Angoon. Turn Point will be the site of a hydroelectric plant for power generation for Angoon, which is now powered by a diesel generator. 

We embarked on this mission in the morning, leaving from the seaplane dock on kayaks. We had to cross the Stillwater Anchorage inlet and saw a pack of seals and an immature bald eagle on the way.

The crew getting ready for the crossing.

Dexter and Landon crossing the Inlet.

We arrived after thirty minutes of paddling and quickly got to work. Finding the CMTs was rather challenging. Cody and Angel, high schoolers who had worked on the CMTs previously, were a part of the team, and they showed us the location of the CMTs athough we still struggled to trudge through the muddy terrain. We began by extracting five cores from each tree: one in the scar, one above the scar, one on the opposite side from the scar, and one on each side ninety degrees around the tree from the scar. For each tree, we hoped to be able to crossdate the scar core with the other cores, allowing us to obtain its age (the age of the scarring of the trees). Once we started coring, though, we realized that mst of the scar surfaces were too rotted for direct sampling. However, we tried coring next to the scars, and we noticed that roughly at the depth of the scar, the core became extremely sappy – in many cases, so sappy that we could not continue boring. We attribute this to a key spruce defense mechanism – when harmed, the wound is flushed with sap. This worked perfectly to the Tlingit’s advantage, allowing them to easily collect sap, and to ours as well, hopefully allowing us to effectively date the scars without actually coring into them. Essentially, the sap is a proxy for the scar. We adjusted our strategy to take two cores from each CMT, one just to the left of the scar, and one just to the right. By the end of the day, we cored around 15 CMTs.

Cody, Landon, and Dexter extracting cores.

Dr. Wiles extracting a core.

After a long day of coring, we returned to the kayaks and began the journey back across the inlet. This paddle was difficult, as the tide was heartily fighting our strokes. Fortunately, many of us still managed to join the bull kelp club, a distinctive organization constituted of those who have eaten raw bull kelp. It was salty and very slimy.

The extracted cores must dry for a couple of weeks, but will be processed at the Wooster tree ring lab. Upon obtaining dates and results from further analysis, the information will be shared with the Alaska Youth Stewards, contributing to and expanding upon their work with the CMTs.

The work of Keck SEAK25 is funded by the Keck Geology Consortium and the National Science Foundation.

Guest bloggers SEAK2025: We began Day 2 at Angoon High School, learning about student research focused on the preservation of Culturally Modified Trees (CMTs). A CMT is any tree that has been modified by indigenous people for cultural or practical reasons. This often includes bark removal for sap harvesting or building material. The group’s project is rooted at the intersection between culture and mathematics, or ethnomathematics. The team of students worked to preserve a cluster of CMTs on Admiralty Island using Light Detection and Ranging (LiDAR) imaging, creating a digitized 3D model of each CMT. We would later have the opportunity to see CMTs at two different localities on Admiralty Island during our third day in Angoon.

Image: Frank Coenraad (of Chatham School District) orienting everyone with CMT research. Under the direction of Frank, the team of Angoon High students placed first at a regional conference in Juneau. They will compete at the Advancing Indigenous People in STEM (AISES) National Conference in Minneapolis, Minnesota, held in October 2025.

After an exciting start to our day, we delivered a presentation on the principles and practices of Dendrochronology to Alaska Youth Stewards (AYS) crew members and faculty. The presentation included field and lab methods, data interpretation, and how we each plan on using dendrochronology for further research.

Image: KECK students presenting to AYS crew members and faculty. Angoon High School, Angoon, Alaska.

 Image: AYS crew members getting hands-on experience learning how to properly mount tree cores.

Image: Nick Wiesenberg teaching students how to analyze tree cores under a microscope after they’ve been mounted and sanded.

After the morning presentations, we set out to explore low tide along the coast; the low tides during our stay were especially low. Referred to as negative low tides, these tides occur when the water level drops below the average low tide zone, exposing areas that are typically submerged. Below are some of the critters and settings observed during the course of the negative tide – the AYS group also explained the traditional uses of some of the seaweed.

We concluded our day collaborating with an ongoing project, led by S’eiltin Jamiann Hasselquist, that seeks to restore Tlingit burial sites to their former glory. We focused our efforts on a cemetery off of Killisnoo Rd. south of Angoon proper. A major effort was cleaning up the site and rolling back the moss and roots masses that have grown over the site. The team revealed grave sites that were covered.

The work of Keck SEAK25 is funded by the Keck Geology Consortium and the National Science Foundation.

Guest bloggers – SEAK25: The SEAK Team traveled to Juneau Alaska from Wooster where they had been learning the basic of tree-ring dating and dendroclimatic analyses,

After spending a couple days in Juneau, our Keck SEAK 2025 Team took a seaplane to Angoon.

Seaplane at the airport waiting for takeoff! Half the team traveled to Angoon on the amphibious float plane (above) and the other half traveled via the Beaver (below) on floats.

Alaska Seaplanes Beaver on floats.

A view of Angoon’s west beach, the old ferry dock, and the first cemetery site (located next to the church, white building on the hill).

Upon arrival, we met with the Angoon Alaska Youth Stewards (AYS) group. AYS “employs a new generation of environmental and cultural leaders to care for [their] lands, waters, and communities” (Alaska Youth Stewards, 2025).

Our first meeting with the AYS crew at the forest service cabin, talking logistics about the next couple of days.

An AYS crew member coring a tree for the first time!

Another AYS corer!

We took a brief lunch and reconvened in the afternoon with S’eiltin Jamiann Hasselquist. Jamiann told us her story: She was born and raised in downtown Juneau, but her mother was from Angoon. Jamiann is involved with Haa Tóoch Lichéesh (HTL), a nonprofit that has organized Orange Shirt Day events, ocean dips, and cemetery cleanup (Juneau Empire, 2024). To honor her mother and give back to the community of Angoon, Jamiann has undertaken the large task of cleaning up and restoring some of the local cemeteries. We and the AYS crew joined in Jamiann’s efforts.

During cleanup, we uncovered a massive slab under the shrubbery. Jamiann cleaned it off, looking for any engravings.

Jamiann posing with the a headstone that we uncovered and stood up.  Prior to cleanup, this headstone was buried underneath the road.

Also on Day 1, we visited a second site with a massive obelisk. Here, we focused on clearing the weeds and cutting down a tree so the obelisk was more visible from town. 

AYS, Jamiann, and SEAK 25 with the obelisk.

Panorama looking west toward the offshore to Chicagof Island.

References

Reid, M. (Ḵaa Yahaayí Shkalneegi). (2024). Resilient peoples and place: Catalyzing healing – a Q&A with S’eiltin Jamiann Hasselquist. Juneau Empire. https://www.juneauempire.com/news/resilient-peoples-and-place-catalyzing-healing-a-qeiltin-jamiann-hasselquist/

Sustainable Southeast Partnership. (2025). Alaska Youth Stewards. Sustainable Southeast Partnership. https://sustainablesoutheast.net/sub_focus_area/alaskan-youth-stewards/

The work of Keck SEAK25 is funded by the Keck Geology Consortium and the National Science Foundation.

Special thanks to Nat McCoy and Dr. Pollock for their hard work on the Earth Sciences 2024-2025 Annual Report. You can access the report through this link.

Guest Bloggers SEAK25 (Keck – Southeast Alaska 2025) – Dendrochronological methods are a key part to our research team’s success. While analyzing and drawing conclusions from data is essential, it is equally as important to ensure the proper collection, preparation, and handling of samples and extraction of ring measurements. There are many key steps to this process in dendrochronology, that when done correctly, ensures the success of a research team.

Taking samples
Tree cores are extracted using an increment borer. By manually drilling the auger into a tree, the core is preserved inside the increment borer with minor injury to the tree. The core extractor, a half circular metal tray, then fits into the auger bit. After cranking the handle counter clockwise, the core then fully separates from the body of the tree. Pulling the core extractor out of the auger allows the extraction of a tree core.

Increment borer.

Selecting the right tree within a stand is crucial to obtaining a good sample. It is important to consider factors such as tree health and direction of lean before coring. Trees that lean excessively can be more difficult to core, as the wood is under more directed pressure. We aimed for trees that stand tall, with little to no lean. If there is a slight lean, then we cored perpendicular to the direction of the lean. When coring we were sure that the auger aimed to the heart of the tree and did not enter at an angle. Depending on the thickness of the tree, two separate cores are required to get data on the entire diameter of the tree. Smaller trees may only require one coring through the full diameter.

Storing and labeling samples
After extracting cores from trees, samples must be properly stored and labeled. The cores are carefully removed from the extractor tray of the increment borer storing the in a plastic straw. It is important to keep the end of the straw near the opening of the auger to ensure the entire core is preserved in case the core itself is broken and is extracted in multiple pieces. Once the sample is safely inside of the plastic straw, the straw ends are folded in to keep the sample in place. The plastic straws we use have holes throughout for proper drying of the sample.

Plastic straws used for sample storage.

It is critical to label the samples immediately after putting them in the plastic straw to avoid mislabeling and confusion. Samples are labeled by their tree ID. This tree ID is given based on research location and sample number. The red cedar cores from Klawock, Alaska were from the “Lower Steelhead” site. They were marked with the label LSRC, standing for “Lower Steelhead Red Cedar.” Each tree from the site was assigned a number as it was cored,;LSRC01 was the first tree cored. The label is written directly on the plastic straw to keep the samples organized. Assuming there are two cores from each tree, each core should have both an “A” and “B” sample, taken from opposite sides of the tree. If they are stored in separate straws, “A” or “B” should be written after the tree ID (eg. LSRC01 A). If it is not clear which end of the core is which, labeling the inside “pith” could also be helpful for future analysis. Tree IDs are used during the marking and cross dating process to identify particular cores, so accurate identification is important.

Once the samples are labeled and stored in the straws, they can be taken back to the lab where they will air dry inside of the plastic straw for anywhere from a couple days to several weeks. Having a fully dried core will lessen the likelihood of warping or cracking when it is glued to a mount.

Prepping core samples for analyses
Once the cores have been dried, they are placed in wooden core mounts. Cores are glued into the mounts with the grain of the wood oriented vertically. The cores are then secured using tape every 2 to 3 inches. The mounts are then labeled with the sample name. Once the samples are mounted they are ready to be sanded. This process begins with placing the core upside down on the belt sander. The core is first belt sanded on 80 to 150 grit then 180 to 220 grit. The cores should be sanded approximately to the thickness of a quarter above the line of the wood mount. The samples are then hand sanded depending on the softness of the type of wood. For example, yellow cedar is harder than red cedar so it was hand sanded using 600 grit then 800 grit sandpaper. Red cedar is softer so it was hand sanded with 800 grit.

Mounted and labeled cores.

A sample after being belt sanded.

Scanning samples
Once the sanding process was completed, and the wood anatomy was clear and scratches were removed the cores are ready for scanning. We used a flatbed photo scanner to scan the cores (2400 dpi). The scanned images were then uploaded to CooRecorder, a software used for tree-ring dating and analysis (Maxwell and Larsson, 2021). CooRecorder allows users to click and place a point on the boundary between each ring, capturing annual layers within a tree. We placed points on the earlywood-latewood boundary, capturing the end of each growing season. This boundary can be identified by the distinct changes in color between latewood and earlywood, latewood being tighter-grained and darker than the more porous and lighter-colored earlywood. We then measured the distances between ring boundaries (individual ring thicknesses). A master ring-width chronology of red cedars already in hand from the area (our master chronology) was used as a dating reference. Given that cores we measured and the series in the mater chronology were from the same region and experienced the same climate signals, we expected the widths to match to some extent. This is an an important step in recognizing any mistakes in dating or any unusual growth in the trees. The CooRecorder software can also display the latewood blue intensity, which is shown in the image below (a subject for a later blog post, blue intensity is a fascinating parameter that we are excited to analyze later this week). The final step for each core was ensuring the latewood blue boxes were parallel to the ring thus accurately representing the boundaries of each ring. Overall, the dating using CooRecorder is a tedious yet rewarding process, and upon completion, we had dates and ring-width measurements for each core and could proceed to chronology development.

Screenshot of the CooRecorder software with the latewood blue intensity parameter turned on.

Quality Control of the Cross dating
Another important step in the dendrochronological process is the building of a “master” chronology. A master chronology is a collection of tree ring series of a particular species that is generally accepted to be a reliably dated and can be compared with newly measured ring – width series. In our case we added to the master chronology which was then used to evaluate the climate signal in the trees.

An example run that compared two of our Western red cedar chronologies, using the COFECHA program (Holmes 1983). 

For example, an existing Western redcedar master chronology may be used to check the reliability of a different red cedar chronology from a similar area. This is accomplished by comparing the relative growth of the trees over time. If the chronologies display a similar growth pattern as measured by correlations (i.e. years of faster and slower growth are during similar years), then the new chronology can likely be trusted as being a well-dated and potentially useful dataset. This process of cross-referencing an existing chronology with a new one is called cross dating, and is an important principle in dendrochronology. Our research team has built a new master chronology for Western redc edars using the program COFECHA (Holmes, 1983) that consist of 60 ring-width series. To our knowledge, this is the most robust and complete chronology of red cedar in Alaska to date. Thus, this is an exciting opportunity to use this new chronology for potentially innovative projects.

Preliminary investigation of the ring width series
Once samples have been properly collected and prepared for analysis, a preliminary investigation of how the data might be useful can be performed. Before identifying the scope of a study, one needs to know what phenomenon in particular the tree ring chronology is being used to study. This is easily accomplished by loading a tree ring chronology and comparing it with an existing observational dataset. Often, in dendrochronology, this will be a climatic data set (average, minimum and maximum temperatures, precipitation, etc.) because trees are the most sensitive to climatic variables. However, finding which climatic variable a particular chronology is sensitive to can be trickier.

A correlation field demonstrating the high correlation between our Western red cedar chronology and winter minimum temperature in Alaska. Note the high positive correlations of the tree-ring site and much of Alaska and Western Canada.

To accomplish this, our research team loaded our master Alaskan red cedar chronology into an online climate analysis tool called KNMI Climate Explorer (Trouet & Van Oldenborgh, 2013), a useful website that contains a plethora of observational and modeled climatic datasets. This website also allows the user to correlate  datasets, which is how our team, through trial and error, found a climatic variable that our chronology is sensitive to. For this particular red cedar chronology, we found that the chronology is sensitive to winter minimum temperatures. This means that our chronology dataset has a high positive correlation with the observational dataset for this particular variable. The team is working on understanding why winter minimum temperatures are most strongly correlated with the site.

Red cedar chronology (red) the blue line is the sample size. The 1876 ring is the most narrow of the record. Note the increase in tree growth over the past century.

Next steps
Now that we have identified a climatic variable to which our chronology is sensitive, our team can begin more detailed analysis of the chronology. Each of the SEAK25 Team will pick a more narrow topic on which to complete an in-depth research project throughout the course of the summer and the following school year. Potential projects might include an evaluation of the evolution of the Aleutian low-pressure system, an investigation of the Indian Ocean teleconnection recognized in western red cedar, a reconstruction of Great Lakes water levels, and possible snowpack reconstructions in the Sierra Nevada.

References cited
Holmes, R. L. (1983). Computer-assisted quality control in tree-ring dating and measurement, Tree Ring Research, v.43, 69-78.

Maxwell, R. S., & Larsson, L. A. (2021). Measuring tree-ring widths using the CooRecorder software application. Dendrochronologia, 67, 125841.

Trouet, V., & Van Oldenborgh, G. J. (2013). KNMI Climate Explorer: a web-based research tool for high-resolution paleoclimatology. Tree-Ring Research, 69(1), 3-13.

Figure 1. Title page of Amanda’s thesis including one of the key figures.

Amanda Flory (class of 2025) completed a thesis that investigated the interplay between the pace of the ocean-atmosphere climate in the Northeast Pacific that is dominated by Pacific Decadal Variability along with the volcanically-forced coolings inferred from tree-ring records. Her title page (above) summarizes the results with several known volcanic intervals linked with decade-long coolings. These coolings are inferred from a tree ring-width series located in coastal Southeast Alaska (Dude Mountain, Ketchikan, Alaska). In addition to her thesis work Amanda presented her results at the meeting of the Geological Society of America in the Spring of 2025. The take-home here is that the variability as recorded in the tree-ring record appears to be a combination internal variability of the Northeast Pacific [1] and volcanic forcing [2] contributing to the decadal variability in the climate.

Figure 2. The author (left) cores a yellow cedar (Cupressus nootkatensis) – Nick (middle) and Proto provide support.

Figure 3. Comparisons of Sitka, AK temperature records for the months of December through October of the growth year correlated with the Dude Mountain ring-width record.

This climate/tree-ring comparison (Figure 2) examines the moving correlation over time (since 1857) is based on a running 35-year correlation. Correlations change from positive (blue) to negative (red) and back to positive. This non-stationary response temperature is puzzling and is likely complex reflecting the ecological and climate-related thresholds at the site. Amanda explored the correlation between ocean heat content ([3]; see Figure 1: title page) and tree growth. The strong and steady relationship between the ocean heat content and growth suggests that the near-coastal tree-ring site is dominated by the ocean-atmosphere system immediately offshore.

Figure 4. Key volcanic events that correspond with decades of cooling.

As is the case with most theses, more crucial questions are raised and will continue to be investigated. These include continuing the examination of the yellow cedar climate response as well as applying new analyses that seek to tease out the volcanic response from the internal response of the Pacific Decadal variability in the record.

Acknowledgements: This work was supported by the National Science Foundation Grant AGS-2002454. We would like to thank Klawock’s Alaskan Youth Stewards (AYS) group for their expertise and guidance while conducting field work.

References:

[1] Schneider, N., and Cornuelle, B.D., 2005, The Forcing of the Pacific Decadal Oscillation:, doi:10.1175/JCLI3527.1.

[2] Wang, T., Otterå, O.H., Gao, Y., and Wang, H., 2012, The response of the North Pacific Decadal Variability to strong tropical volcanic eruptions: Climate Dynamics, doi:10.1007/s00382-012-1373-5

[3] Levitus, S. et al., 2012, World Ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010: Geophysical Research.