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

posted in: Publications, Research | 0

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.

 

 

What’s our fieldwork like in Greenland? Watch and see

posted in: Field work, Greenland | 0

The Uummannaq region of West Greenland is a spectacular area of steep cliffs, icefalls, and long fjords.  While on a NASA-funded research project to better understand the connections between water in these fjords and the glaciers terminating there, I’ve had the extraordinary opportunity to fly, camp, hike, and work in this landscape.  Now, you can get a taste for our work in a 4-minute movie set to music, that draws on video footage from 2015 fieldwork, and time lapse imagery from 2013.  I hope you enjoy it!

 

Thanks to Sophie Gilbert (University of Idaho) for producing this movie.

Press write-up of AGU presentation

One of my two presentations at the AGU fall meeting this year is the subject of a well done blog post.  In the presentation, my co-authors and I reported the detection of over one million icequakes produced near the terminus of a tidewater glacier in west Greenland.  Study of these icequakes will allow us to better understand the factors controlling the flow of glacier ice, and ultimately allow scientists to make more precise predictions of sea level rise.

We’re presently about half way through the meeting this year and its been a good week so far.  During the Saturday and Sunday prior to the beginning of the AGU fall meeting, I participated in a planning workshop to lay the groundwork for a monitoring network to observe ice-ocean interactions in Greenland.  I made the case for the value of seismology in understanding tidewater glacier dynamics.

My second invited presentation is a poster on Thursday afternoon. I’ll be sharing observations and interpretations of high-rate velocity variations near the front of one of Greenland’s largest ocean-terminating glaciers.  The presentation is C43B-0805 High-resolution, terrestrial radar velocity observations and model results reveal a strong bed at stable, tidewater Rink Isbræ, West Greenland.

 

 

IMG_7397
A seismometer deployed at the terminus of a west Greenland glacier for two years, between 2013 and 2015. This station recorded over a million icequakes, year-round.

Promotion to UTIG research staff

posted in: Research | 0

UTIG_logo-UTWordMarkI’m pleased to report that I’ve been promoted from Postdoctoral Fellow to Research Associate, at the University of Texas Institute for Geophysics in Austin, Texas. I’ll be continuing my research into glaciological processes and glacier change through the use of seismology, terrestrial radar interferometry, satellite and airborne imagery, and other geophysical tools. More papers and proposals, the currency of our trade, are on their way. I look forward to continuing and initiating collaborations, with students and fellow PIs, in the years to come.

Third successful Greenland field season

After spending September in Greenland, the UT/KU team has returned from our third and final field season in the Uummannaq region of western Greenland.  We recovered equipment that has been monitoring tidewater glaciers in the region for two years, as well as made a set of shorter-term, higher-resolution observations that required us to camp adjacent to one of the glaciers for 10 days.  We’re looking forward to working with the data, and sharing our results at this fall’s AGU meeting, future conferences, and in publications.

The seismometers, GPS, timelapse cameras, and weather stations we recovered were in great shape.  We also recorded excellent terrestrial interferometric radar observations (in spite of strong, consistent katabatic winds) and more seismic and GPS data.  Due to the lateness of our field work (our previous field work has been in July and August), we also got to experience the transition in seasons, from fall to winter.  This meant wonderful twilight, rich red tundra, and the first snows on the mountain tops.

You can read more about this interdisciplinary, NASA-funded project here.

Published: Subglacial water flow observed through seismic tremor

posted in: Publications, Research | 0

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

posted in: Publications, Research | 0

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.

Plenary talk at the Earthscope National Meeting

posted in: Outreach, Research | 0

Tim will be attending the 2015 Earthscope National Meeting in Stowe, VT, to deliver a plenary talk on the use of seismology and GPS to learn about glacier dynamics.  This talk, on June 15th, will cover some of the projects Tim has been involved with in Alaska to understand subglacial hydrology, fast glacier flow, and iceberg calving, as well as future opportunities in Alaska and Greenland.

The meeting, from June 15-17, will broadly be discussing Earth’s deformation in North America and beyond, and the future of the Earthscope project.

Time series of calving icequakes can be used to track variations in iceberg calving rate, for example, how calving responds to rising and falling diurnal ocean tides.
Time series of calving icequakes can be used to track variations in iceberg calving rate, for example, how calving responds to rising and falling diurnal ocean tides.

The extended abstract for my presentation is below.

Understanding the Processes Driving Glacier Change with Alaskan Seismic and GPS Data

Timothy C. Bartholomaus, Christopher F. Larsen, Michael E. West, Shad O’Neel, Ginny Catania

Worldwide, glaciers and ice sheets are losing mass and increasing global sea level (Shepherd and others, 2012; Gardner and others, 2013). However, the processes controlling these changes are not well understood. Changes in glacier hydrology and iceberg calving can both increase rates of glacier flow, thereby hastening delivering of ice to the ocean and low elevation regions. The understanding of these two processes is not yet sufficient to reliably include them in ice flow models for the prediction of sea level rise.

The application of seismology and GPS techniques within glaciology allows insight into glacier hydrology and iceberg calving processes. At Yahtse Glacier, a tidewater glacier in Alaska, we seismically quantified calving at unprecedented tidal to seasonal timescales. Tracking of calving-generated icequakes reveals that calving of large icebergs is significantly more likely to occur during falling and low tides than during rising and high tides. We also observe that calving fluxes are greater during the late summer and fall than during winter, suggesting that, on the coast of Alaska, submarine melt of glacier termini is likely a dominant control on the calving rate (Bartholomaus and others, 2013). Background seismic noise (i.e., tremor) also offers glaciological insight. Tremor amplitude rises and falls seasonally and after storms, synchronously with subglacial discharge. Thus, subglacial discharge variations can be quantified at tidewater locations where discharge has been previously unknown.

At Yahtse Glacier and Kennicott Glacier, also in Alaska, we use GPS to observe contrasting responses in glacier motion to melt, rain, and lake-drainage events (Bartholomaus and others, 2008). At Kennicott, speedup responses are short-lived and glacier motion quickly returns to background levels. Yahtse Glacier’s response to hydrologic events is long-lived and leads to progressively slower flow over the course of the summer, demonstrating that in some cases changes in subglacial water routing are not reversible on daily to weekly timescales.

Together, seismic and GPS data offer views of glacier responses to environmental change with temporal resolution that is not available through approximately weekly satellite images. These highly resolved observations allow physical insight that improves our understanding of glacier physics, eventually allowing for better inclusion of glacier dynamical processes in ice flow models. Going forward, Earthscope’s Transportable Array in Alaska expands on the present opportunity to remotely track iceberg calving across coastal Alaska.­ New terrestrial radar interferometers offer a more complete view of ice flow variability by combining the spatial resolution of satellite imagery with the temporal resolution of GPS.

 

Tim joins editorial board of Frontiers in Cryospheric Science

posted in: Publications, Service | 0

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

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