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Cryospheric Sciences

GIA

Cryo-Adventures – The Glacial Isostatic Adjustment (GIA) Training School: Personal and Virtual Attendance

Group photo in front of Lantmäteriet. [Photo courtesy of Daniel Vallin (Lantmäteriet)]

The 2019 Glacial Isostatic Adjustment (GIA) Training School was hosted by Lantmäteriet (the Swedish Mapping, Cadastral, and Land Registration Authority) in Gävle, Sweden from 26 – 30 August. GIA is the response of the solid Earth to past and present-day changes of glaciers and ice sheets. Research interests in GIA span the geosciences: from regional planning applications (reclamation/flooding of land due to uplift/subsidence) to constraining past ice sheet history. For this blog, two attendees interviewed lecturers and participants to summarise the five-day training school.


From over 160 applicants, 41 students and early-career researchers from 28 countries (on 6 continents!) were selected to attend the school. Instruction included a mixture of lectures and practical modeling exercises – with ample time for discussions over coffee (or, Fika). An interesting aspect of the training school was that all lectures were live-streamed. Up to 60 people were tuned-in at any given time, and there have been more than 500 individual views of the online content.

“The participants at the 2019 GIA training school were amazing – they came from a wide range of scientific, geographic, and cultural backgrounds, and they threw themselves into the task of extracting as much information as possible from the lecturers and other participants!” said Dr. Pippa Whitehouse, Associate Professor of Geography at Durham University and one of the organizers of the Training School. “In fact, [the students’] input was vital to shaping the content of the entire training school: at the start of the week we challenged them to come up with a series of questions they wanted us to answer, and I think we just about covered everything by the end of the week.”

The lectures and exercises covered a wide range of topics including: History of Land Uplift Research (Martin Ekman), Introduction to GIA (Glenn Milne and Erik Ivins), GIA Modeling (Giorgio Spada), Geodetic GIA Observations (Tonie Van Dam), Sea-level Change (Riccardo Riva), GIA-triggered Earthquakes (Rebekka Steffen), Ice Sheet Modeling (Frank Pattyn), Continental Record of Ice Sheet and Relative Sea Level History (Mike Bentley), Seafloor Record of Ice Sheet History (Julia Wellner), Coupled GIA Modeling and Data-Model Comparison (Pippa Whitehouse), Antarctic Earth Structure and Geologic Record (Terry Wilson), Antarctica Earth Structure and Rheology from Seismology (Doug Wiens), and 3D GIA Modelling (Wouter van der Wal).

Modeling exercises utilized the forth-coming SELEN4 (SealEveL EquatioN solver – preprint available here) by Giorgio Spada and Daniele Melini, and f.ETISh (Fast Elementary Thermomechanical Ice Sheet Model) by Frank Pattyn. A break from the classroom came in the form of a day-long field trip to ancient, uplifted shorelines from the end of the last ice age that now sit 500m above sea level, modern beaches (where the effects of isostatic rebound can be viewed), an enormous esker (a long, winding ridge of sediment transported by meltwater), and an equally impressive 6m-tall glacial erratic (a large, glacially-transported boulder).

Holger Steffen showing students (and lecturers) how GIA has forced the city of Gävle to relocate their harbor, one of the largest in Sweden. [Photo by Peter Matheny (OSU)].

 “This GIA training school really opened my eyes to the diversity of methods that are being employed to approach problems related to GIA,” said Jennifer Taylor, Ph.D. student in the Structure, Tectonics, and Metamorphic Petrology group at Department of Earth and Environmental Sciences, University of Minnesota. Jennifer attended the Training School in person. She was impressed by the breadth of earth science disciplines represented at the course, and the variety of datasets and modeling methods employed in the practical component. “As a researcher who typically works on million-year timescales,” she added, “it was fascinating to visit a region where people have been living with the dramatic results of rapid uplift throughout recorded human history.” Sweden, as well as other regions of Scandinavia, continue to experience significant effects of glacial isostatic rebound, with uplift rates on the order of several mm per year.

Dr. Deirdre Ryan, a postdoc at the University of Bremen’s Center for Marine Environmental Sciences (MARUM), attended the Training School virtually. While Dr. Ryan enjoyed the lectures and was glad for the opportunity to attend virtually, the inability for virtual attendees to participate in the practical component of the course with instructor supervision meant that they missed out on some of the most useful sessions of the week. “However, I think this is something that can be addressed,” she said. “I’m really excited to see that the virtual conference experience can be as fulfilling as in-person attendance without the requirement of travel and can really serve to reduce science’s carbon footprint.”

Financial support for the Training School was contributed by the National Science Foundation (NSF) through the Antarctic (ANET) component of the Polar Earth Observing Network (POLENET) project, the Scientific Committee on Antarctic Research (SCAR) through the Solid Earth Response and influence on Cryosphere Evolution (SERCE) program, the International Association of Cryospheric Sciences (IACS), the European Geosciences Union (EGU), and DTU Space.

The conference organizers were Stephanie Konfal (Ohio State University), Terry Wilson (Ohio State University), Rebekka Steffen (Lantmäteriet), Martin Lidberg (Lantmäteriet), Pippa Whitehouse (Durham University), and Holger Steffen (Lantmäteriet).

This was the fourth such training school, which has been alternatively hosted by Lantmäteriet and the Ohio State University in 2009, 2011, and 2015. All lectures from the School were recorded and are freely available on the POLENET’s website.

Further reading

Edited by Jenny Turton


 

Libby Ives is a PhD candidate in the Department of Geosciences at the University of Wisconsin-Milwaukee. She studies the sedimentary records left behind by glaciers both in the Pleistocene and in the rock record, with a special focus on the Late Paleozoic Ice Age. You can find her on twitter @glaciogeoLives

 

 

 

Peter Matheny is a PhD student in Geodetic Sciences at the Ohio State University, and is currently working with the POLENET project. When not taking classes, he works on improving the speed at which we can process large networks of GPS stations to realise global reference frames.

 

 

Image of the Week – The solid Earth: softer than you might think!

Rebounding beach in the Canadian Artic [Credit : Mike Beauregard distributed by Wikimedia Commons]

Global sea level is rising and will continue to do so over the next century, as has once again been shown in the recent IPCC special report on 1.5°C. But did you know that, in some places of our planet, local sea level is actually falling, and this due to rising of the continent itself?! Where is this happening? In places where huge ice sheets used to cover the land surface during the last ice age, such as Scandinavia, Canada, or Siberia. Even though these ice sheets melted several thousands of years ago, the land that once lied under them is still rising in reaction to the release of their previous burden. This is what we call Glacial Isostatic Adjustment or GIA. Where does this adjustment come from? Our Earth is not as solid as you would think…


Our Image of the Week represents a layered beach located in Nunavut, in the Canadian Arctic. This specific landform is caused by the glacial rebound of the Arctic coastline resulting from the response of the lithosphere to the melting of the Laurentide Ice sheet, an ice sheet that used to cover the North American continent until less than 10 000 years ago.

Earth during Last Ice Age [Credit: Wikimedia Commons]

What is Glacial Isostatic Adjustment?

Imagine sitting on a very comfy couch, watching a movie. At the end of the movie, the couch has perfectly adapted to the shape of your body. Once you get up, you’re still able to see where you’ve been sitting, as the couch takes a little time to get back to its original form. Well… this is exactly what happens with the Earth’s crust and mantle. To understand this, you need to visualize the internal structure of our planet Earth, which is layered in spherical shells: under our feet lie the rocky tectonic plates, which constitute the Earth’s crust. These crusty plates – whose thickness varies between a few kilometers under oceans to a few tens of kilometers under the continents – are floating on a viscous layer, called the mantle. It is almost 3000 kilometers thick and actually slowly flows like a liquid, at a speed of a few centimeters per year.

Even though the Earth’s crust is a very strong material, the pressure applied by an ice sheet thick of several kilometers is so important that the crust will locally deform under the heavy ice mass, sinking down into the viscous mantle. That’s what happened over large areas of the Northern Hemisphere that were covered by ice masses during the last ice age, and what is still happening in the remaining ice sheets of Greenland and Antarctica, which have been depressing the Earth’s crust beneath them for thousands of years.

Just like for the couch in the example above, when the weight is removed, the mantle rebounds, carrying with it the overlying crust. Over the 20 000 years since the last glacial maximum, lands now relieved of their previous ice-burden are gradually rebounding. The Earth’s delayed response to the variation of mass on its surface is explained by the viscous character of the Earth’s mantle.

Glacial Isostatic Adjustment [Credit: Wikimedia Commons]

Why is it important to take it into account?

Even though the Siberian, Scandinavian and Laurentide ice sheets melted several thousands of years ago (causing a rise in global sea level), these regions that were previously glaciated are still locally emerging to compensate the loss of their overlying weight. The level of the coastline relative to the local sea-level thus increases. One says that the “relative sea level” is falling, and this at a rate that is essentially determined by the rate of the post-glacial rebound (which can exceed 1 cm/year in some areas, as shown in the figure below!). The rates of relative sea level can be influenced even at sites that are quite far away from the centres of the last glaciation, although it is much less significant.

Rate of the post-glacial rebound [Credit: NASA, Wikimedia Commons]

A good understanding of glacial isostatic adjustment is important to distinguish the different components and contributors to a local sea-level evolution: what part is due to the uplift of the land? And what part is due to the rising of global sea-level?
In addition, glacial isostatic adjustment also impacts the behaviour of  modern Greenland and Antarctic ice sheets. By influencing the geometry of the underlying bedrock, it will impact the sensitivity of the ice sheet to global warming and thus the glacial isostatic adjustment itself: this is a vicious circle!

The problem is that glacial isostatic adjustment also depends on the local properties of the Earth’s crust and mantle, which are not constant at the Earth’s surface. A lot of work is still needed to understand all of this properly. Luckily, since NASA launched GRACE – a satellite mission that maps variations in the Earth’s gravity field –  in 2002, scientists have observations they can use to constrain their models and improve their understanding of this complicated matter.

Further reading

Edited by Clara Burgard and Sophie Berger