New papers on glacier thinning, form of MSGLs, and subglacial discharge plumes

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Several new papers published this summer exemplify the diversity of our research group’s interests and methodologies.  Thanks to the outstanding scientists and co-authors who led these efforts: Denis Felikson, Rebecca Jackson, and Matteo Spagnolo.

The first of these, published in Nature Geoscience, uses analytical analysis of glacier flow to explain the extent of inland thinning in Greenland.  This work received a variety of media coverage in the scientific and popular press, including on Boise State Public Radio and a regional newspaper, the Inlander.

The second, in Geophysical Research Letters, draws on observations of buoyant freshwater plumes in glacierized fjords and assesses their relationship to the subglacial discharge that drives them.

The third, in the Journal of Geophysical Research, uses two dimensional spectral analysis to reveal the ice stream produced bedforms consist of multiple, distinct, wavelength peaks.  These peaks coarsen down flow and are consistent with self-organizing processes.  This paper was selected as an Editor’s Highlight:

This paper reports the first application of the 2-dimensional discrete Fourier transform method to describing and analyzing the orientation-specific roughness elements of mega-scale glacial lineations (MSGL). Applying the technique to several case study examples reveals characteristic, orientation-specific roughness scales that guide process-related inferences on MSGL formation and evolution.

 

 

A figure from Spagnolo et al., 2017 shows the dominant wavelengths of mega-scale glacial lineations and their downstream variation.

New paper reveals the factors that allow glacier advance

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While glacier advance is extremely rare, study of advancing glaciers offers a more complete picture of glacier dynamics and the factors that enable such advances.  In Alaska, Yahtse Glacier is the fastest advancing glacier.  After a 40-km 20th century retreat, it has advanced 2.5 km since 1990, and is thickening by several meters per year over its terminus.  During this advance, the terminal stresses have transitioned from tensile to compressive, and the driving stresses have dropped by a factor of 3.  All of these changes at the Yahtse terminus have occurred despite net mass loss over the entire Yahtse Glacier basin, reflected by thinning in the upper reaches of the glacier.

Along flow and seasonal variations in ice speed, over the course of Yahtse Glacier’s advance.

 

We suggest that continued growth and progradation of a submarine morainal bank, and a steep icefall which dynamically isolates the terminus region from the upper basin, are critical for the sustained advance of Yahtse Glacier.

This work was led by Joey Durkin, a Ph.D. student at Cornell University, and published in Frontiers in Earth Science.

Understanding subglacial hydrology through seismology

Last week, I visited the Boise State Geosciences department to give a seminar on the use of seismology to understand subglacial water flow and sediment transport.  I reviewed two of my recent papers, published in GRL (this in 2015, and this in 2016), and also presented some of the initial results from my work with graduate student, Margot Vore, from Taku Glacier.  I enjoyed getting to know some other Idaho geophysicists and identifying new opportunities for collaboration.

bartholomaus_bsu

New papers on ice-ocean interactions, glacier seismicity and subglacial hydrology accepted

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Three new papers are now in press in Geophysical Research Letters, Journal of Glaciology and the Annals of Glaciology.  These papers are:

 

Bartholomaus, T. C., L. A. Stearns, D. A. Sutherland, E. L. Shroyer, J. D. Nash, R. Walker, G. Catania, D. Felikson, D. Carroll, M. J. Fried, B. Noël, M. van den Broeke (in press), Contrasts in the response of adjacent fjords and glaciers to surface melt in western Greenland, Annals of Glaciology.

In which we integrate glaciological and oceanographic observations from the west coast of Greenland to demonstrate how subglacial hydrology has contrasting effects on the glacier and fjord dynamics within neighboring systems.

Gimbert, F., V. C. Tsai, J. M. Amundson, T. C. Bartholomaus, and J. I. Walter (in press), Sub-seasonal pressure, geometry and sediment transport changes observed in subglacial channels, Geophysical Research Letters.

In which we demonstrate how seismic and discharge measurements can be combined to identify how subglacial pressure gradients within Rothlisberger channels and channel size vary over the course of the melt season at a glacier in Alaska.  Additionally, we discuss variations in sediment transport and the impact of flowing water on glacier motion.

Brinkerhoff, D., C. R. Meyer, E. Bueler, M. Truffer, and T. C. Bartholomaus (in press), Inversion of a glacier hydrology model, Annals of Glaciology, 57(72).

In which we constrain the evolution of the subglacial hydrologic system through measurements of glacier water discharge, glacier motion, and estimates of water inputs.

 

 

Published: Subglacial water flow observed through seismic tremor

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A new study, published August 10 in Geophysical Research Letters, demonstrates how seismic tremor can be used to track variations in the flow of water emerging from the termini of marine-terminating glaciers.  This tremor, sometimes referred to as “seismic noise,” is recorded on seismometers, common earthquake monitoring instruments.  Measurements of subglacial discharge variation at tidewater glaciers, which thus far have not been achieved, are a critical step towards understanding the present and future behavior of some of the largest and most rapidly-changing glaciers on earth–those that end in the ocean.  Not only does subglacial water  control fast glacier flow, but subglacial water discharged into fjords promotes glacier melt below sea level and can erode and redeposit glacier-stabilizing sediment at glacier fronts.  These newly-reported observations of glaciohydraulic tremor open a broad new avenue through which to study these important phenomena.  The study was authored by Tim Bartholomaus, Jason Amundson, Jake Walter, Shad O’Neel, Mike West and Chris Larsen.

This study has been reported on the radio by the Austin, TX, NPR affiliate, and by EOS, the American Geophysical Union’s news publication.  Additional coverage includes the Aug. 31 issue of the magazine Engineering News Record, as well as several websites, including, grist.org, futurity.org, phys.org, and Environmental Monitor.

You can read the UT press release about our study here.

Subglacial discharge upwells at the terminus of Yahtse Glacier
Subglacial discharge upwells at the terminus of Yahtse Glacier.  Now, increases and decreases in the amount of subglacial discharge can be detected through the subtle ground vibrations produced by the flowing water.

Three new papers now in review

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Over the last month, I’ve had the pleasure of submitting three, new, first-author papers for peer review with a diverse set of co-authors.  These papers are a combination of wrapping up old projects (including the last of my Ph.D.-related work) from Alaska, and also the first of new work coming out of Greenland.  These manuscripts include unprecedented observations of tidewater glacier subglacial discharge through analysis of seismic tremor, characterization of the tremendous importance of subglacial discharge on the dynamics of adjacent tidewater glaciers and fjords in Greenland, and high-fidelity seismic monitoring of tidal and seasonal variations in iceberg calving.  This is an exciting time, and I count myself lucky to be working with an excellent group of scientists.  My teams and I are hoping for a few new C.V. line items later this year!

The papers in review are as follows:

Bartholomaus, T. C., J. M. Amundson, J. I. Walter, S. O’Neel, M. E. West, and C. F. Larsen,  Subglacial discharge at tidewater glaciers revealed by seismic tremor, Under review at Geophysical Research Letters.

Bartholomaus, T. C., C. F. Larsen, M. E. West, S. O’Neel, E. C. Pettit, and M. Truffer,  Tidal and seasonal variations in calving flux observed with passive seismology, Under review at Journal of Geophysical Research.

Bartholomaus, T.C., L. A. Stearns, D. A. Sutherland, E. L. Shroyer, J. D. Nash, R. Walker, G. Catania, D. Felikson, D. Carroll, M. J. Fried, B. Noël, M. van den Broeke, Contrasts in the response of adjacent fjords and glaciers to surface melt in western Greenland, Under review at Annals of Glaciology.

Tim joins editorial board of Frontiers in Cryospheric Science

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This new journal, expected to launch in May 2015, responds to the rapid growth in cryospheric research and provides authors with a more open, transparent, and rapid review and publication experience.  The Frontiers publishing house has grown rapidly since its founding in 2007 by scientists responding to the question, “If reinvented today, what would academic publishing look like?”

All articles published through Frontiers in Cryospheric Science will be open-access (gold) and peer-reviewed quickly and independently by reviewers.  Prior to publication, authors and reviewers work interactively to ensure that the submitted article is as flawless as possible.  For their efforts, reviewers are recognized in the published article.  A unique user interface facilitates this rapid and straightforward review process.  Tim Bartholomaus has joined Frontiers in Cryospheric Science as an Associate Editor.

I encourage you to learn more about Frontiers in Cryospheric Science, the Frontiers publishing community, and the Frontiers review system.  Please don’t hesitate to get in touch if you have any questions.

 

Frontiers

Ice sheet model implements extension of Bartholomaus et al. (2011)

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In work from several years ago, co-authors and I developed a model of subglacial and englacial water storage that reproduces some of the characteristic patterns of glacier flow observed in the field.  This work, published in the Journal of Glaciology, was motivated by observations from Kennicott Glacier in Alaska, where a large, ice-dammed lake drains beneath the glacier annually.  During the flood, water delivery to the glacier temporarily overwhelms the glacier’s ability to convey that water through and beneath the glacier, and the glacier flow speed increases by a factor of 5.

Now, in recent work by Ed Bueler, head of the PISM ice sheet modeling group at UAF, the model described in Bartholomaus et al. (2011) has been extended in a manner that allows it to be implemented efficiently at a large scale.  This distributed version  of the hydrology model can now be used within PISM and other ice sheet models to simulate water flow at the base of, for example, the Greenland and Antarctic ice sheets.  You can read more about Ed’s advance, published in the Journal of Glaciology, here.

Bueler 2014- Extending the lumped subglacial-englacial hydrology model of Bartholomaus and other (2011)

New perspective on calving in press at Nature Geoscience

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A new study, of which I am a co-author, examines globally-collected observations of iceberg calving and novel model results to present a new framework for understanding this important mass loss process.

Our study explains why calving rates vary so greatly over time, and how small changes in the environment can lead to tremendous changes in calving activity.  We show for the first time that calving belongs to a class of processes termed “self-organized critical.”  These processes occur in the same manner over many orders of magnitude such that there is no single, characteristic event size.  The calving terminus self-organizes to the point where it is always at the cusp of collapse. This property makes iceberg calving very challenging to predict.  However, in our manuscript, we demonstrate one potential solution for addressing this challenge and including self-organized critical calving in ice flow models.

Our paper will be published in a forthcoming issue of the journal Nature Geoscience.