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)

Novel views of iceberg calving presented at PARCA

At the annual meeting of the Program for Arctic Regional Climate Assessment (PARCA) hosted at the NASA Goddard Space Flight Center, I’ll be presenting new data that allow a more complete view of the iceberg calving process.  These data include ground-based radar interferometry, seismic, and ocean current observations that reveal how major calving events proceed over 10s of hours before, during and after an iceberg detaches from the terminus.  This PARCA presentation will be the first view of these data, collected during the 2014 summer at the terminus of Rink Isbrae in West Greenland.  Further analyses of these data, taken together, will contribute to our understand of how and why calving occurs at Greenland’s largest outlet glaciers, and what the effects of these events are on the glaciers and adjacent ocean.

The PARCA meeting takes place on January 27th in Greenbelt, Maryland.  You can read more about the project that supported collection of this data here.

Radar interferogram from Rink Isbrae, Greenland
Unwrapped radar interferogram from Rink Isbrae in Greenland, following a major calving event. The colors represent relative rates of motion towards the radar interferometer. Data is shown here in a polar reference frame, with distance between the radar shown along the x-axis and look direction shown along the y-axis.

Presentations and sessions at AGU

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This year, I’ll be giving an invited talk in one of the ice/ocean interaction sessions, and convening another session focused on iceberg calving and submarine melt at the termini of tidewater glaciers. My talk, at 11:20 on Wednesday in MW 3007, will describe how we can use seismic noise to observe subglacial discharge at tidewater glaciers (C32B-05). My convened session is co-chaired with Ellyn Enderlin and covers a wide range of oceanographic and glaciological observations and models.  For this session:

  • The talks will be on Thursday at 4pm in MW 3007 (C44B).
  • Posters are on Tuesday afternoon in MW (C23A).  The posters for two other similar sessions are at the same time, so I’m expecting that we’ll have a lively, well-attended poster session.

This is also the first year for which I have scheduled the glaciology program on behalf of the AGU Cryosphere focus group.  The planning for this meeting took place over the spring, summer and fall of this last year. I’m wishing everyone a great meeting, and that conflicts in the schedules of glaciologist conference attendees are kept to a minimum!

Tim participates in international workshop to guide Greenland ice-ocean research

During the last several days, I have taken part in an international workshop to identify the major gaps in the scientific community’s understanding of interactions between the Greenland Ice Sheet and its surrounding ocean.

The workshop on Greenland Ice Sheet-Ocean Interactions, under the acronym GROCE, was hosted by the Alfred Wegener Institute, in Bremerhaven, Germany.  Over the two day meeting, ~28 scientists from Germany, Norway, the UK, Poland, Japan, Canada, the US and other countries framed the questions we considered most essential for understanding Greenland’s rapid changes, as well as the strategies and resources necessary to respond to those questions.  It was interesting and exciting to hear the commonalities and differences in research priorities from the broad cross section of glaciologists and oceanographers in attendance.

The report produced to summarize our workshop will be used to help guide funding agencies and the proposal efforts of the broader scientific community.

Next stop for me: San Francisco.  The annual meeting of the American Geophysical Union starts there on Monday.

Workshop attendees
Attendees at the 2014 GROCE workshop

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.

Watch a presentation of my research

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I recently presented an overview of my research program to date at the weekly seminar of the Univ. of Texas Institute for Geophysics.  You can view it here.

In this talk, I describe my past and ongoing research into how ocean-terminating glaciers can rapidly lose mass through their termini.  This week, I’ll be traveling to Purdue University to make a similar presentation.  An abstract for this seminar is below:

The largest and most rapidly changing glaciers on Earth flow into the ocean. Ice loss from these glaciers will be the largest contributor to sea level rise in coming centuries and is also the least certain component of the sea level budget. These uncertainties are driven in large part by the poor understanding of two processes by which tidewater glaciers and ice sheets lose ice at their termini: submarine melting by warm ocean water and mechanical iceberg calving. 
The fronts of tidewater glaciers are among the most active and inaccessible geological environments.  These challenges have limited the long duration, high resolution calving and melt measurements that yield insight. Using seismology and oceanography, I identify the magnitudes and variability of submarine melt and iceberg calving at Yahtse Glacier, a major tidewater glacier in southern Alaska. I find that the submarine portion of the glacier terminus melts at over 10 m/d during much of the year. In addition, cavitation of icebergs beneath the sea surface can generate seismometer-recorded “icequakes,” revealing that calving varies seasonally and in response to ocean tides. Seismic tremor also offers the first ever view of subglacial discharge from a tidewater glacier.  Discharge increases during late summer, which promotes submarine melt.  Together, these multidiscipline observations improve our understanding of the geophysical processes responsible for rapid ice loss across the cryosphere.

An extraordinary field season

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Earlier this month, our joint Univ. of Texas and Univ. of Kansas team returned from West Greenland, where we collected data regarding the behavior of ocean-terminating glaciers in a major fjord system.

Many of the sensors we visited, including GPS receivers, seismometers, weather stations and time lapse cameras, had been recording data for a year, since we installed them in August 2013.  While in the field, we also had the opportunity to camp at the terminus of Rink Isbrae (71.5 degrees north latitude) for 10 days.  During that time of focused terminus observations, we were able to scan the terminus with a radar system every 2.5 minutes to detect detailed variations in the speed at which the glacier was moving.  Our team of 5 scientists had a great time working together and developing a better sense for how these beautiful and rapidly changing glacier/ocean systems work.

Together, our data will allow us to better understand the factors that lead to increasing and decreasing glacier stability.  Ultimately, this understanding will allow the glaciological community to make better projections of future glacier change- the leading contributor to the increased sea level anticipated this century.

In this photograph, our field team resets a GPS station on the ice.  Stations such as these allow us to identify the response of the glaciers to ice melt, rain, glacier thinning, and iceberg calving events.

Preparing for AGU

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At the annual meeting this December, I’ll be making an invited presentation and co-convening a different session.  On behalf of AGU’s Cryosphere focus group, I am serving on the meeting planning committee.

The fall meeting of the American Geophysical Union is the largest meeting of geophysicists, including cryosphere and climate scientists, worldwide.  This year, my involvement in the annual meeting is greater than ever.  I’ve been invited to give a presentation on the links between glaciers that flow into the ocean and their fjords, and I’m co-convening a different session on a similar topic.  With Adam Winstral, a snow scientist, I’m serving on the meeting’s program committee to assist with scheduling the nearly 40 different sessions that will be available under the Cryosphere umbrella at this year’s conference.

Understanding iceberg calving

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I’ve recently co-authored an accessible review of recent research into iceberg calving.  You can read it by clicking here.

Approximately half of the ice loss from the Greenland Ice Sheet occurs where glaciers flow directly into the ocean.  At the ice/ocean interface, glacier ice is lost through fracturing (i.e., iceberg calving) and melting in contact with the relatively warm ocean.  The rates of this ice loss has increased in recent years, which has drawn significant attention within the glaciological community to the calving and submarine melting processes.  However, there is much that we still need to understand about calving before we can reliably predict how rapidly glacier might calve in the future.

For a newsletter targeted at a broad audience, Jeremy Bassis and I have summarized the existing research on iceberg calving, and some of the ways in which we can improve on our understanding of calving.  The other articles within this newsletter summarize other perspectives on the relationship between the Greenland Ice Sheet and its surrounding oceans.  The full newsletter, from which I’ve excerpted our piece on calving, is available here.