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.

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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.

Experiential Learning on Ice (with some water)

January 19th, 2014

Tom Lowell, Aaron Diefendorf and four students from the University of Cincinnati met up with the Wooster Geologists to core Browns Lake. We thank Marvin Sandy, who manages the bog for the Nature Conservancy for guidance and permission to do this work.
coresite

Coring Browns Lake from an ice platform on a winters day in Northeast Ohio. Four cores were taken – the longest of which was 17 meters. The mud in the cores is a record of 15,000 years of environmental change since the last Ice Age.
Browns Lake Bog is own by the Ohio Department of Natural Resources and managed by the Nature Conservancy.

Browns Lake Bog is owned by the Ohio Department of Natural Resources and managed by the Nature Conservancy.

pitcher

Pitcher plants are among the special biology of the bog. Note the ice forming within the pitcher.

auger

First a hole is augured to determine water depth in the basin. It is about 5 feet deep with 4-6 inches of ice.

A look at the drilling rig - anchored in the ice, tied down with ice screws.

A look at the drilling rig – anchored in the ice, tied down with ice screws and straps.

 

pipe

A look down the long axis of the drill pipe – note the corer sticking out of the ice stored in the lake to prevent it from freezing. The water is the warmest place on the site.

Tom explains the theory and Doug and Nick move into the practice phase.

Tom, the core boss,  explains the theory and Doug and Nick move into the practice phase.

humor

Tom and Michael share a coring joke – it help to have a sense of humor standing on ice for 6 hours at 15 degrees F with a breeze.

meter

Another meter of core is brought up – ready to be described, wrapped and archived. About half of the 40 meters of core went to Cincinnati for further analyses.

Lunch on the boardwalk

Lunch on the boardwalk

oscar_andy

Oscar and Andy take a break from the core archiving. Note the water that moves up through the hole in the ice. The weight of the rig and crew cause elastic and some plastic deformation to occur – after the rig is removed the ice slowly pops back into shape.

The last of the gear moves to the parking lot.

The last of the gear moves to the parking lot.

Thanks to Jesse Wiles for the photography.

The geese point the way back to Wooster. Thanks to Jesse Wiles for the photography.

 

 

 

 

 

 

A Wooster geologist’s summer research experience in The Bahamas: Sarah Bender (’15) and climate and sea level change over the past 6,000 years

August 20th, 2013

SB coverSarah Bender (’15) and Sarah Frederick (’15) had the opportunity this summer to complete National Science Foundation funded Research Experiences for Undergraduates (REUs). Each spent a good part of their summer completing a research project under the mentorship of accomplished and enthusiastic geologists. Sarah Bender (on the left above) worked under the mentorship of Dr. Lisa Park Boush (’88, center in the photo), a geology professor at the University of Akron, and Kristina Brady (’03, on the right), a curator at the University of Minnesota. A Wooster geology team! This is Sarah’s summer research story in her words and images. (Sarah Frederick’s story is in the previous post.)

This summer I had the pleasure of working with a group of seven interns and four mentors on Eleuthera Island, Bahamas and at the University of Minnesota Twin Cities and Duluth. For two weeks at the beginning of June, we cored three Bahamian lakes, two being blue holes and the other a coastal pond. The goal of this Research Experience for Undergraduates (REU) was to determine the anthropogenic changes that took place in the past thousands of years in the Bahamas by using proxy data from these lakes. The project was led by a Wooster graduate, Dr. Lisa Park Boush (’88), who like myself, was one of Dr. Mark Wilson’s advisees. One of the other mentors, Kristina Brady, also graduated from Wooster (2003) as Dr. Wiles’ advisee, and is now working at LacCore at the University of Minnesota as a curator.

My team worked on the first blue hole, which we named Duck Pond Blue Hole. Duck Pond Blue Hole is an inland circular body of brackish water located in the southern tip of Eleuthera Island. We hypothesize that there are underground conduits connecting the blue hole to the ocean due to the salinity and the fact that the water level was affected by tides. Cores were taken with hand-operated corers from three different spots along a transect of the lake. Overall, my team recovered over four meters of sediment from the three sites! We also took bathymetry data, depth profiles, and did a vegetation survey around the perimeter of Duck Pond Blue Hole.

SB-1a

Myself, a teammate, and Kristina Brady (’03) capping a core from Duck Pond Blue Hole. Check out our mighty coring vessel!

The other team of interns worked on a coastal pond, located directly behind one of the most beautiful beaches in the world. They cored the pond at three sites and took similar lake profiling data as my team. They also worked on dune profiles with Dr. Ilya Buynevich from Temple University using his GPR machine.

SB-2

The other team of interns worked on a coastal pond, located directly behind one of the most beautiful beaches in the world. They cored the pond at three sites and took similar lake profiling data as my team. They also worked on dune profiles with Dr. Ilya Buynevich from Temple University using his GPR machine.

The rest of the time on Eleuthera was spent exploring the island and learning about its history. We took two day-long field trips in which we saw many geological features as well as archaeological sites. With the help of Dr. Perry Gnivecki and Dr. Mary Jane Berman, both from Miami University, we learned all about the native inhabitants of the Bahamas, the Lucayans. We hope our project will help them understand how they were affected by climate change and the landing of Columbus in 1492. Finally, we got to present our preliminary results to the people of the Bahamas at the Cape Eleuthera Institute.

SB-2.5

My teammates and I presenting Duck Pond Blue Hole at CEI.

After finishing fieldwork, we headed to LacCore, the National Lacustrine Core Repository, at the University of Minnesota in Minneapolis to analyze our data. We logged, split, photographed, and described our cores first. We also did a variety of lab work with core samples such as, carbon-14 dating, SEM, loss on ignition, making smear slides, and shell counts. We also got to work at the Large Lakes Observatory in Duluth, Minnesota using the XRF machine and doing grain size analysis.

SB-3

Myself and a teammate prepping samples for grain size analysis at the Large Lakes Observatory in Duluth.

This lab work took about six weeks to complete and we got some amazing results from it. We used the last few days in Minnesota to write our abstracts and make posters for upcoming conferences. Each person took one aspect of our project to focus on. My abstract and poster focuses on the mollusk communities of Duck Pond Blue Hole and how they may be an indicator for climate and sea level change in the Bahamas over the past 6,000 years.

In order to discover what we found, you will have to visit my teammates at GSA in Denver in October or AGU in San Francisco in December. I hope to be able to make it to the AGU conference to help present my team’s work, however, I won’t be presenting my individual abstract until the spring at a regional GSA meeting. If you want to read more on the project, check out the REU Bahamas page on Facebook or the daily blog we kept throughout the project. Now, it’s off to Byron Bay, Australia, for me! I hope everyone had a great summer and I wish you all a successful fall semester!

Dr. Michael Mann visits Wooster

March 28th, 2013

MichaelMann032713WOOSTER, OHIO–We were honored this week when Dr. Michael E. Mann, one of the world’s foremost climate-change experts and a leader in the efforts to educate the public about anthropogenic effects on the atmosphere, came to Wooster as part of our Richard G. Osgood, Jr., Memorial Lecture series. He gave a public lecture in the nearly-full Gault Recital Hall Wednesday evening (“The Hockey Stick and the Climate Wars: Dispatches from the Front Lines”), and then a Geology Club lecture the next day in Scovel (“The Past as Prologue: Learning from the Climate Changes in Past Centuries”). Students, faculty and staff of the Geology Department also had a wonderfully informative dinner with him in the Wooster Inn.

Michael Mann is very well known in the diverse community that studies climate change in the past, present and future. He was the senior author of a pivotal article in the Intergovernmental Panel on Climate Change (IPCC) Third Scientific Assessment Report in 2001. It set the direction for more than a decade of later climate research. He has written dozens of other papers and two books on climate change. He has received numerous awards, most recently the Hans Oeschger Medal of the European Geosciences Union.

The public Osgood lecture Dr. Mann presented on Wednesday was centered on his latest book. He described the recent scientific history of climate change research and then how he became an “accidental public figure” through the famous “Climategate” theft and publication of private email messages. His stories of attempted congressional interference in his work and that of other climate scientists were astonishing, representing what he calls “the scientization of politics” (where science — or pseudoscience — is used as a political tool).

The image at the top of the page is Dr. Mann near the end of his Osgood Lecture. The image on the screen is of his daughter enjoying a moment in the polar bear pool at the Pittsburgh Zoo and PPG Aquarium. He fears that someday such animals will be found only in zoos because humans “melted their Arctic environment.” Numerous questions and conversations followed.
MannLecture032813Dr. Mann gave a Geology Club presentation this morning in Scovel Hall on some of his scientific work (shown above). He talked about using proxies to model historical climate change and then predict future climate.
WilesMann032813For me one of the best moments was his conversation with Greg Wiles in our dendrochronology lab (above). It was great fun to see how the work of Wooster Geologists is part of the unfolding grand story of what factors control our climate, and why such research is critical in our efforts to cope with future changes.

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

September 11th, 2011

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 20 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.

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