New Impact Crater Discovered Under Greenland

November 17th, 2018

If you’re plugged into science news outlets, you’ve likely seen stories about a very large crater that has been detected underneath Hiawatha Glacier in northwest Greenland (e.g., at Science News).  Here’s the link to the peer-reviewed article in Science Advances, by Kurt Kjær and colleagues. This paper is being touted by some outlets as likely vindication for the “Younger Dryas Impact Hypothesis”, made famous by Firestone et al. (2007). This may sound exciting to science consumers, but for many climate scientists, this is cause for groans, not exhilaration. After seeing the headlines, a few questions that might arise are: 1) How much does Kjær et al. (2018) support Firestone et al. (2007)? 2) Wait, what was Firestone et al. (2007) all about? Actually, the first question might be: 3) What the heck is the Younger Dryas, anyway?

Figure 1 from Kjær et al. (2018), showing the location of the impact crater in northwest Greenland.

Let’s take these in opposite order:

Question 3: What’s the Younger Dryas? It’s the last gasp of the Pleistocene glacial Epoch.  Warming and retreat of the ice sheets didn’t always occur gradually.  Over the course of several thousand years (about 20,000 to 11,700 years ago), the ice retreated in fits and starts.  Often, the warming was abrupt, and often the warming was actually reversed for many years or decades as Earth’s atmosphere and ocean constantly adjusted to the shifting ice cover and long-term warming trend.  The Younger Dryas is the last big cold snap before the relative warmth and stability of the Holocene.  It was long — from 12,900 to 11,700 years ago. The transition both into and out of the Younger Dryas was was also abrupt — like decades or shorter. (Alley 2000)

Temperature and snow/ice accumulation in Greenland over the past 17,000 years (from Alley 2000, p. 9, fig. 12)

Question 2: In 2007, Firestone et al. proposed that a comet exploded over North America, leading to myriad devastations: Widespread wildfires across North America, collapse of the Clovis culture, the extinction of North American megafauna (e.g., woolly mammoths), and the abrupt onset of the Younger Dryas. Firestone et al. proposed a comet in part because there was no impact crater in North America and in part because the geochemical evidence they presented was “more consistent with an impactor that was carbon-rich, nickel–iron-poor”.

What followed was a contentious tear-down of the Firestone hypothesis.  I have 40 papers saved on my computer about this stuff, and it got nasty. Not only were the conclusions disputed, but also the results.  Some scientists presented contrary evidence using similar methods (Paquay et al. 2009; Daulton et al. 2010). Others questioned the validity of evidence presented by Firestone et al. (Buchanan et al. 2008Tian et al. 2011). Some scientists even tried to replicate the results at the same study sites but couldn’t ( Surovell et al. 2009; Haynes et al. 2010). By 2011, Pinter et al. published a paper called “The Younger Dryas impact hypothesis: A requiem”, declaring it dead. Of the original 12 lines of evidence provided by Firestone et al., 7 proved unreproducible, and the others were given alternate explanations, such as non-catastrophic mechanisms (e.g., an uptick in wildfires can be explained by drought) and/or terrestrial origins (e.g., magnetic grains occur many river sediments).

Question 1: So along comes this new paper that says there is an impact crater in North America. That’s big news, right?  Yeah, it’s cool. But are Firestone et al. are vindicated? Absolutely not — at least not yet.  Here’s a few problems that jump out to me about making the leap in logic from “there’s an impact crater in Greenland in the Pleistocene” to the conclusion that this impact caused the Younger Dryas:

  1. The timing.  The authors of the new paper state that the impact probably occurred during the Pleistocene.  That’s about 2,576,000 years of Earth history, and the Younger Dryas is dated down to decades.  Looking deeper at the paper, it seems most likely that the impact was in the later part of the Pleistocene, so it is absolutely possible that it hit at 12,900 years ago. However, even if we give error bars of ± 100 years on the Younger Dryas onset and say the impact had to be during the last 100,000 years of the Pleistocene (the last 3.8%), there’s still a 99.8% chance that the impact did not overlap with the Younger Dryas onset. So it’s too soon; we need to date this crater.
  2. Even if an impact occurred at 12,900 years ago, it doesn’t change the state of the evidence regarding mammoths or humans.  As summarized in several of the above papers, there’s no consensus of evidence for a catastrophe at the Younger Dryas for either.
  3. We still need an explanation for getting out of the Younger Dryas at 11,700 years ago.  And we still need an explanation for the various other abrupt climate shifts apparent in the Greenland ice cores. So the terrestrial mechanisms that caused other events (ice sheet and ocean dynamicscould still cause the Younger Dryas even if an asteroid could, too.
  4. The authors of this new paper are very clear that their geochemistry matches an iron meteorite. Firestone et al. were very clear that their geochemistry matched an iron-poor impactor like a comet.

To their credit, Kjær et al. are appropriately cautious in voicing implications. They never mention the Firestone hypothesis; they are conservative in their dating; and they do not speculate about broader implications beyond “this impact very likely had significant environmental consequences in the Northern Hemisphere and possibly globally”. (It does seem to be one of the top 25 largest in the world.) Now, if it turns out we later find this impact was at 12,900 years ago, that will get me excited.

A lonely Dryas plant in Kennecott, Alaska. (Photo: Alex Crawford)

 

p.s. If you’re wondering, yes, there’s also an Older Dryas period.  It’s similarly cold but much shorter and happened  around 14,000 years ago. Both periods are named after the Dryas genus, which is abundant in Scandinavian lake samples dating to these periods.

Climate Monday: The xkcd Earth Temperature Timeline

April 30th, 2018

It’s the final week of the semester, so it’s time for a little fun in the world of weather and climate visualizations.  One of the toughest things that Geologists have to deal with is conveying a sense of time scales.  It’s difficult for present-day humans to conceive of how long ago (or recent) the Roman Empire or Han Dynasty were, let alone 4.6 billion years of Earth history. We often use interesting comparisons, like how the time gap between Tyrannosaurus (68-66 million years ago) and humans is smaller than the gap between Tyrannosaurus and Stegosaurus (155-150 million years ago).  Sometimes we use analogies, like how an average human lifespan is 0.00000204% of all Earth’s history, which is about the same percentage of your life you just spent reading this paragraph.

With climate change, scientists often are approached with the question: “Climate has changed before, so why is this time worse?” An important is that this time it’s changing very fast, and rapid change is more problematic than gradual change. The faster the change, the harder it is for plants and animals (and humans) to adjust.  But conveying that sense of rapid change can be difficult when our time series are so long, stretching tens of thousands of years.  It rarely looks good on a single powerpoint slide or a single 8 1/2″ by 11″ piece of paper.  You either have to scrunch everything into a very condensed and crowded graph, use an inset box to zoom in on today, or use multiple slides/figures.  Or… you could use the tendency for modern webpages to scroll indefinitely to convey a sense of time.  This is the tactic of the webcomic xkcd.

No, seriously. The main reason for reading the comic is to laugh at the little bits of humor slipped in, but Randall Munroe at xkcd is diligent about scientific research.  The temperature data for the visualization are based on a combination of  HADCRUT4 (from the UK Meteorology Office), the Intergovernmental Panel on Climate Change (IPCC, funded by the UN), and peer-reviewed journal articles in the journals Nature (Shakun et al. 2012), Science (Marcott et al. 2013), and Climate of the Past (Annan and Hargreaves 2013). Those last three are all paleoclimate reconstructions.

Wooster’s Fossils of the Week: Sponge and clam borings that revealed an ancient climate event (Upper Pleistocene of The Bahamas)

April 28th, 2017

This week’s fossils celebrate the publication today of a paper in Nature Geoscience that has been 20 years in the making. The title is: “Sea-level oscillations during the Last Interglacial highstand recorded by Bahamas coral”, and the senior author is the geochronological wizard Bill Thompson (Woods Hole Oceanographic Institution). The junior authors are my Smith College geologist friends Al Curran and Brian White and me.

The paper’s thesis is best told with an explanation of this 2006 image:
This photograph was taken on the island of Great Inagua along the coast. The flat dark surface in the foreground is the top of a fossil coral reef (“Reef I”) formed during the Last Interglacial (LIG) about 123,000 years ago. It was eroded down to this flat surface when sea-level dropped, exposing the reef to waves and eventually terrestrial weathering. The student sitting on this surface is Emily Ann Griffin (’07), one of three I.S. students who helped with parts of this project. (The others were Allison Cornett (’00) and Ann Steward (’07).) Behind Emily Ann is a coral accumulation of a reef (“Reef II”) that grew on the eroded surface after sea-level rose again about 119,000 years ago. These two reefs show, then, that sea-level dropped for about 4000 years, eroding the first reef, and then rose again to its previous level, allowing the second reef to grow. (You can see an unlabeled version of the photograph here.) The photograph at the top of this post is a small version of the same surface.

The significance of this set of reefs is that the erosion surface separating them can be seen throughout the world as evidence of a rapid global sea-level event during the Last Interglacial. Because the LIG had warm climatic conditions similar to what we will likely experience in the near future, it is crucial to know how something as important as sea-level may respond. The only way sea-level can fluctuate like this is if glacial ice volume changes, meaning there must have been an interval of global cooling (producing greater glacial ice volume) that lowered sea-level about 123,000 years ago, and then global warming (melting the ice) that raised it again within 4000 years. As we write in the paper, “This is of great scientific and societal interest because the LIG has often been cited as an analogue for future sea-level change. Estimates of LIG sea-level change, which took place in a world warmer than that of today, are crucial for estimates of future rates of rise under IPCC warming scenarios.” With our evidence we can show a magnitude and timing of an ancient sea-level fluctuation due to climate change.

Much of the paper concerns the dating techniques and issues (which is why Bill Thompson, the essential geochronologist, is the primary author). It is the dating of the corals that makes the story globally useful and significant. Here, though, I want to tell how the surface was discovered in the first place. It is a paleontological tale.

In the summer of 1991 I worked with Al Curran and Brian White on San Salvador Island in The Bahamas. They were concentrating on watery tasks that involved scuba diving, boats and the like, while I stayed on dry land (my preferred environment by far). I explored a famous fossil coral exposure called the Cockburntown Reef (Upper Pleistocene, Eemian) that Brian and Al had carefully mapped out over the past decade. The Bahamian government had recently authorized a new harbor on that part of the coastline and a large section of the fossil reef was dynamited away. The Cockburntown Reef now had a very fresh exposure in the new excavation quite different from the blackened part of the old reef we were used to. Immediately visible was a horizontal surface running through the reef marked by large clam borings called Gastrochaenolites (see below) and small borings (Entobia) made by clionaid sponges (see the image at the top of this post).
Inside the borings were long narrow bivalve shells belonging to the species Coralliophaga coralliophaga (which means “coral eater”; see below) and remnants of an ancient terrestrial soil (a paleosol). This surface was clearly a wave-cut platform later buried under a tropical soil.


My colleagues and I could trace this surface into the old, undynamited part of the Cockburntown Reef, then to other Eemian reefs on San Salvador, and then to other Bahamian islands like Great Inagua in the far south. Eventually this proved to be a global erosion surface described or at least mentioned in many papers, but its significance as an indicator of rapid eustatic sea-level fall and rise was heretofore unrecognized. Finally getting uranium-thorium radioactive dates on the corals above and below the erosion surface placed this surface in a time framework and ultimately as part of the history of global climate change.

This project began 25 years ago with the discovery of small holes left in an eroded surface by humble sponges and clams. Another example of the practical value of paleontology.

References:

Thompson, W.G., Curran, H.A., Wilson, M.A. and White, B. 2011. Sea-level oscillations during the Last Interglacial highstand recorded by Bahamas coral. Nature Geoscience (DOI: 10.1038/NGEO1253).

White, B.H., Curran, H.A. and Wilson, M.A. 1998. Bahamian coral reefs yield evidence of a brief sea-level lowstand during the last interglacial. Carbonates and Evaporites 13: 10-22.

Wilson, M.A., Curran, H.A. and White, B. 1998. Paleontological evidence of a brief global sea-level event during the last interglacial. Lethaia 31: 241-250.

[Originally posted September 11, 2011. Some updates and editing.]

Wooster Geologists participate in the historic March For Science on Earth Day, 2017

April 22nd, 2017

Wooster, Ohio — It was a chilly day downtown, but several hundred people gathered for the national March For Science. We were one of over 500 local events across the country advocating for science awareness, education and funding. Thank you very much for retired Wooster Professor of Biology Lyn Loveless for organizing such a complex meeting with speakers and break-out discussions in local businesses. It was a great success. Above are some of the signs held by children in attendance. Several Wooster Geologists were in the diverse crowd, and some participated directly.

One view of the attendees. We all see the distinctive profile of Dr. Wiles in the foreground. Kelli Baxstrom may recognize someone on the far right!

One of the speakers was ace Wooster physicist and former dean Dr. Shila Garg. Note her coat on this mid-April day.

I include this photo (taken by Wooster political scientist Matt Krain) of Dr. Wiles and me to show my Paleontological Society colleagues that I wore The Shirt, even if no one noticed under the jacket.

One of the break-out sessions was on climate change. Greg Wiles and Clara Deck (’17) did great outreach work explaining their research to the large gathering. Wooster’s paleoclimate and climate change research and education is making a difference. Visit the Tree-Ring Lab website to see more details about the operation.

It was an inspiring afternoon, especially seeing the many young scientists and scientists-to-be who participated. Of course, for someone my age it is astonishing that we have to advocate for something so self-evidently beneficial as science, but such are our times.

What we learned in Climate Change (Geology 210, Spring 2016)

May 31st, 2016

boulder

A dedicated group of geologists, physicists, archaeologists, political scientists, biologists, english and history majors joined forces to learn a bit about Climate Change in the natural laboratory of Northeast Ohio. Here they surround a glacial erratic in Secrest Arboretum of the OARDC – where The Ohio State University and the National Weather Service has meteorological records extending back to the late 1800s CE. The Arboretum also has an extensive collection of stands of trees from around the world that are used in our climate studies below (special thanks to Joe Cochran (OSU) for permission to work at Secrest).

The first project: the glacial transition in a sediment core from  Browns Lake Bog

rundown

Dr. Thomas Lowell gives the rundown at Browns Lake Bog – Tom is a professor at the University of Cincinnati and long-time collaborator and the core boss.

lab

Initial description of the 5 meter core – we obtained two radiocarbon ages, measured magnetic susceptibility, loss on ignition, in addition to core description and sediment analyses.

The Upshot of the Lake Work – The two ages were chosen at transitions in the character of the peat and mineral matter – we identified a major shift at the time of the Bolling – Allerod warming and at the cooling of the Younger Dryas.  The abrupt climate changes (ACCs) and discussion of how the world moves from the Pleistocene to the Holocene is brought home to Ohio in this core (Figure below). It is exciting to explore how these ACCs affected NE-Ohio’s ecosystems and physical landscapes.

master_bog

Project 2: Tree Ring Dating of the Biggio Barn

rundown

The barn owner gives the rundown on the history and possible ages of the hand hewn timber frame. The dating of the barn project introduced the class to the science of tree-rings.

vincent

Hong Kong dendrochronologist, Vincent shows the class how by standing on two milk crates he cores a beam – the instructor adds a stabilizing foot to Vincent’s precarious sampling strategy.

The upshot of Barn Dating: Ten of the beams from the Biggio Barn were cut in the spring of 1840 CE. The building then was likely constructed shortly after that cut date.  A copy of the report to the owner from the class can be found here. The ring-width data obtained in this study are used in drought studies below. The Wooster Tree Ring lab has dated over 60 barns and houses in Ohio and PA (this video describes the process and some of the science).

Project 3a: Extracting a Temperature Proxy Record from Larch in Kamchatka
Vincent Hui, Abbey Martin, Sarah McGrath, Matthew Shearer, Ann Wilkinson

The purpose of this study was to analyze Kamchatka larch (Larix cajandery Mayr.) tree ring widths from Fareast, Russia. The team standardized the chronology using two methods, (1)  negative exponential, and (2) regional curve standardization (RCS), and they then compared how the standardization technique influenced correlations. Both standardized series were correlated with meteorological records showing high positive correlations for summer temperatures. The RCS showed stronger correlations and was used for NTREND comparison, temperature reconstruction, and spectral analysis. Together these correlations and comparisons showed the larch primarily responds to summer temperature and can be used to reconstruct summer temperatures.

kamchatka

The Kamchatka team of researchers (without Vincent) who did the study. They are posing at Wooster Memorial Park where a recent planting of 700 trees and prairie will sequester more carbon in the future than the previous agricultural land use at the site.

Figure2

ntrendConclusions: 
1 – The Kamchatka larch tree-ring widths are most sensitive to summer (May through September) temperatures.

2 – The team recommends the region curve standardization method) RCS method for standardization with a sample size of 190 series.

3 – The RCS series showed similar trends as the NTREND series, suggesting the Kamchatka site follows the same trends as much of the northern hemisphere.

4 – Ring-widths show a general increase in temperature over the last 350 years for the interior of Kamchatka. This is unprecedented over the past 300 years and is consistent with other proxies such as glaciers.

Project 3b: Past climate inferences using data from Johnson Woods
 Sharron Osterman, Annette Hilton, Cameron Steckbeck, Gina Malfatti, Amineh AlBashair

  • tst
  • The Johnson Woods team assembled a newly compiled data set originally sampled in 1985 by Dr. Ed Cook (LDEO), by the Wooster Tree Ring Lab in 2003 and most recently updated by Dr. Justin Maxwell (Indiana State University). They found there was a marked release in the tree ring record across northern Ohio about the time of European Settlement in the region. This may be in part due to the disturbance in the record, however it could also persist due to the positive response that tree growth has to summer precipitation.
  • Slide2
  • Slide1Above is a histogram showing the correlations of the Johnson Woods ring-width series and monthly precipitation and temperature records from the OARDC spanning 1880 to 2014 CE. The trees are a record of summer precipitation (positive correlation) and favor wet summers. These trees are negatively correlated with high summer temperatures.

One Question on the final exam:
What is the Climate response of European Larch to climate of Ohio – Secrest Arboretum (and why might this exploration be relevant?).

  • coring1

Obtaining high quality cores for ring-width chronologies from European Larch at Secrest Arboretum.

coring2

 The upshot here is the ring-width chronology below. The class worked on this as part of the final exam and found that similar to the oaks in the region, the European Larch is sensitive to summer precipitation and is stressed by high summer temperatures. The tailing off of the ring-widths during recent decades could be the result of warmer summer temperatures – a hypothesis that needs testing. The relevance of this study is that as climate changes in the high latitudes of Europe and Asia, where these larch dominate – it may be the case, that warming may stress the species leading to decreases in bioproductivity – these ideas need further work to test if this is a viable hypothesis.

Plot 1

jw

A day in Johnson Woods – the full class in the rain.

jw

danWe also learned that Dan Misinay (’16) is a pretty fair teaching assistant.

milling

The class wanders around the gas power plant on the Wooster campus – three years ago the college transitioned from coal burning to natural gas – the carbon dioxide emissions on campus have been cut in half. However, now the College buys its power for cooling (air conditioning) off campus from the grid, where much of the electricity is powered by coal, but with a growing portfolio of clean energy sources (special thanks to Lanny Whitaker who showed us the plant and explained where our energy comes from – thank you). We also thank Nick Wiesenberg (our able Geology Technician) for his knowledge of trees, barn dating and general troubleshooting,  Tom Lowell and his students for the high quality sediment cores, our TA Dan and a host of tree-ring scientists who contributed data to our efforts in this course. Special thanks too – to the Secrest Arboretum. A portion of the Kamchatka tree-ring record was supported by NSF- AGS – 1202218.

Wooster Geologists (and a Wooster Chemist) visit Brown’s Lake Bog

May 21st, 2015

1 Greg with fernsI was privileged today to visit Brown’s Lake Bog, a Nature Conservancy preserve, with Greg Wiles, Nick Wiesenberg, and Kim Carter (Chemistry ’16). Greg and Nick have been here many times with students and colleagues, including some epic sessions of ice drilling. It is an important site for both the rare plants that live here and the geological context of a relict kame-and-kettle topography from the last glaciation. Greg has set up over the years a series of shallow well measuring stations and has cored several of the old-growth oaks for tree-ring analyses. Kim, a student of Paul Edmiston, was looking for sites to place Osorb samples to adsorb various chemicals in run-off waters. I was along just for fun.

2 Brown's Lake Bog signThe Nature Conservancy maintains the 80-acre site, including trails and a boardwalk through the woods to the bog itself.

3 Kame at Brown's Lake BogNear the head of the bog trail is a nice view of a plowed kame. This is a geomorphological feature formed when sediment accumulated in a depression on a glacial ice sheet and then was deposited as the ice melted. The bog itself is a kettle, the result of a melting block of ice buried in the sediment produced at the margin of a retreating glacier.

4 Greg and transducerGreg retrieving a transducer, which measures water level changes, from one of his wells.

5 Nick and downloaded dataNick takes the transducer, cleans it up, and then downloads the data into a laptop computer. It shows hourly records of temperature and water level changes in the well. (I know, that’s George W. Bush peaking around the results window. Ask Nick why!)

6 Nick and rain collectorNick is here recovering a rainwater sample from a collector. This water is isotopically examined by researchers at the University of Cincinnati as part of a long-term project.

7 Brown's Lake Bog 585Here is the beautiful bog itself, slowly being filled by sediment and encroaching shrubbery. The water is surrounded by a thick floating mat of Sphagnum moss.

8 Sarracenia purpurea & SphagnumThe Sphagnum mat supports a fascinating array of rare plants. It is an acidic, nutrient-poor environment, so the plants are quite specialized.

9 Sarracenia purpurea pitchers 585The stars of the boggy botanical delights are the Northern Pitcher Plants (Sarracenia purpurea). These trap insects inside their fluid-filled cavities surrounded by slippery walls. That is how they obtain most of their nutrients.

10 Sarracenia purpurea flowerThese tall, downward-facing blooms are the flowers of the pitcher plants. I imagine they are high above the pitchers so the pollinating insects don’t get eaten!

11 Drosera_rotundifolia 585Finally, here’s a nice Round-Leaved Sundew (Drosera rotundifolia), another cool carnivorous plant common on the Sphagnum mat.

What a delightful day with my colleagues!

Three Days on Ice

January 25th, 2015

group

Dr. Lowell and a crew from the University of Cincinnati spent thee days with us on the ice at Browns Lake Bog. The objectives were to take a series of long cores from the ice platform at the bog and, in the big lake,  to take a short surface core that the Wooster Geomorphology class will study. In addition we installed a series of four nested monitoring wells in the sediments around the lake.coring_theoryThe coring crew taking the deep core – about 24 meters in two meters of water depth.

coring_sed_water

The sediment-water interface on TV – note the screen on the ice that helped guide the coring process to be sure the actual sediment-water interface was captured.

sed_water

Subsampling the upper core to be sure the modern sediments at the interface were in the bag.

coring_1

The ongoing coring.

probe1

Measuring dissolved oxygen, pH, TDS, ORP and Temperature along a depth profile.

 

instrument_wellMeasuring the same parameters in four sets of nested monitoring wells  – one deep, one shallow.

on_iceDrilling holes in the ice along  grid and measuring depth profiles in the big lake.

ice_holesOne of the ice hole teams.

probingThe mud probing team – not a glamorous job but necessary.

water_levelMeasuring the water levels in the well after bailing.

weather_stationThe weather station installed at the bog. 

well_prepDrilling a series of holes to act as a screen in the monitoring wells.

pumpingPumping the wells for isotope samples and installing a transducer to keep track of water levels.

shootingErika takes aim at the upper branches of a white oak – she will extract the water from these twigs and buds and measure their isotopic composition.

shavingPealing the twigs and bagging them up for transport.

our_coreTom recovering the surface core from the middle of Browns Lake – the big lake. Now the ball is in our court to do some analysis. Great thanks go out to the Core Boss and his crew.



Last Fieldtrip for Climate Change

November 13th, 2014

GROUP

As the weather cools – the Wooster Geology Climate Change class ventured out in the field one more time. For the remainder of the semester we will try to get some work done. Two sites were visited – the Cedar Creek Mastodon Site and the OARDC.

excavationTwo weeks ago a pit was dug from our coring sites to the Mastodon excavation site. The mission was to link the cores to the archaeological site.

pit

The general stratigraphy of the mastodon site. The muds have a high calcium carbonate content that helped preserve the bones and tusk. Note the plow horizon about 25 cm down – the trip also focused on the agricultural history of Ohio and the role it plays in climate change.

anomalyJeff Dilyard, who hosted us at the site, explains to the class that a GPR (ground penetrating radar) survey identified an anomaly at this location. Isabel probed the area (see below) and “clunked” on a tile.

probingIsabel above used a tile probe to investigate the subsurface (note the chin method she is employing).

tileWhat is a “tile”? above is an old drainage tile from the site. This one is plugged with mud and the plugging was the reason the mastodon was discovered. New tiles were installed last year and the digging brought up the original tooth of the mastodon. Tile and draining of the Midwest allowed for our great agricultural history. In addition, the tile and draining allowed widespread plowing that released the carbon in naturally sequestered organic rich wetland soils to the atmosphere.

in_pitThe crucial end of the backhoe pit where probing and sampling links the bog cores to the mastodon site.

group_no_till

A quick stop ate the Triplett-Van Doren Experimental Plot. For over 50 years a variety of experiments have been underway here. We discussed the side-by-side no-till and mold board plowed sites and their ability to sequester carbon. Not plowing (no-till) sequesters carbon and mitigates erosion. Less carbon dioxide to the atmosphere and less sediment flux on the landscape.

no_till

A darker colored soil in the core barrel above shows more carbon in the soil relative to the one below.

DR

A quick stop at Secrest Arboretum to view the famous Dawn Redwoods. Under the proper conditions these trees can grow a meter each year. Our tree-ring data from this stand helps define the optimum conditions for their growth. Planting trees sequesters carbon and helps out in lots of other ways as well.

weather

In addition to the no-till fields and trees at Secrest – there is a meteorological record that spans more than 120 years (note how Tom – far left, seems to be the only student listening to the instructor). These instruments have been keeping track of climate and we will use it to compare with our tree ring study. Our tree ring project asks the question: during the time of European Settlement in Ohio what were the climate conditions like? (precipitation and temperature) and could the widespread deforestation and tile and draining of the region have perturbed the climate (see this video for more on this subject). This question is relevant to the ever-present striving of climate scientists to investigate the relative roles of natural climate variability and anthropogenic change.

 

 

 

 

Wooster Geologists return to the Cedar Creek Bog and Excavation Site

October 25th, 2014

DigOverview102514WOOSTER, OHIO–Greg Wiles and I got to experience a bit of field archaeology today at the Cedar Creek Mastodon excavation site. Greg’s Climate change class has visited the site and its associated bog twice this semester: once to do some soil probing and exploration, and then again to extract a core from the bog. This time Greg and I went to consult with the chief archaeologist of the site, Nigel Brush of Ashland University. Nigel wanted our opinions on the stratigraphy of the dig, especially those parts associated with mastodon remains and flint artifacts. The hypothesis the archaeologists are testing is that the mastodon bones and flint blades are part of an ancient butchery site.  It was a joy to join our friends on this fantastic Fall day.

BonesFlagged102514Who doesn’t love an archaeology site? All that enthusiastic hard work with brushes, spades and trowels revealing hidden treasures. Those little orange flags above are tagging bits of mastodon bone that the volunteer excavators have uncovered for mapping and collection. Several schools are represented at this site, and at least a couple dozen citizen scientists.

HannahJim102514Wooster is represented at the dig by archaeology professor Nick Kardulias, along with two of his students shown above. Hannah Matulek is on the left; Jim Torpy on the right.

BoneFragment102514Here is some mastodon bone embedded in one of the excavation walls. The bones are scattered, with some large pieces and many small fragments.

Sieving102514This is the line of sieves for sorting through the excavated sediment. Pleasant enough work today, but I can imagine it’s not so fun in the rain and sleet.

GregSoilProbing102514And now for our bit of work. Greg went off into the bog with a soil probe to plan out a new trench to be dug by the landowner. This trench will help correlate the strata in the excavation with what Greg and his students have cored from the bog.

StratView102514I spent most of my time in the excavations examining the simple layering of the sediments. At the bottom we have a coarse conglomerate with cobble-sized rounded grains. The bones and artifacts lie on top of and among these clasts. Above that unit is a matrix-supported conglomeratic mud with broken rock fragments. At the top is a loam representing the disturbed (plowed) part of the section.

MudWithClasts102514This is a closer view of that middle unit with the “floating” angular rock fragments. My quick assessment (just a suggestion!) is that the coarse gravels beneath are part of a deltaic complex feeding into the bog, which was at the time a marl lake. The mud-with-clasts above it is a debris flow from the surrounding elevations that cascaded down the creek channel and its banks, entombing the bones and artifacts under a slurry of muddy debris. There is scattered charcoal throughout this unit and the top of the cobbles below. Maybe a forest fire denuded the upstream slopes and led to a rain-soaked mudslide? Then again, the charcoal could have come from an ancient barbecue of the mastodon meat.

In any case, Greg and I had a great time visiting our archaeological colleagues on such a fine day.

 

Dating Houses and Reconstructing Climate

September 22nd, 2014

porchThe Wooster Geology Climate Change class spent a beautiful fall day in Stony Creek, Ohio coring beams in three structures of historical significance. They will determine the cut dates (calendar dates when the timber for the houses were felled) for the homeowners and then examine the tree-ring data that results to help reconstruct drought for the region. The class will write a report for the homeowner as part of the project. The Wooster tree-ring lab has dated over 50 buildings. Many of the reports are archived here.

willy2

Willy coring a hand hewn beam with an increment borer in the basement of one of the structures.

dan

Dan cores into the white oak beam as Meredith keeps the utilities at bay.

 julia

Julia identifies the outer (bark year) rings of a large oak beam and sets the spoon to extract the core.

haloMeredith and Haley team up to extract another core from a structure.

mounting2Zach shows how the 5 mm core is mounted in a slotted core mount.

coreSarah glues the carefully oriented core into the mount.

mounting

Orienting the core properly is crucial for the next step of sanding the surface. This interdisciplinary group of historians, archaeologists, communication studies and geologists will learn bit about history of Ohio while learning some of the statistics of climate change and earning a Q (quantitative) course credit.

houseThe group should be able to determine when the timber was cut to build this restored structure. Sometime in early November the analyses should be completed.

extra_coringSome extracurricular coring of young white pines in the area.

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