BLOG

Artificial Glacier Surges at Kumtor Mine

Posted by William Colgan on July 27, 2015
Applied Glaciology, New Research / No Comments

Jamieson and colleagues published a very neat investigation of the applied glaciology challenges at Kumtor Mine, Kyrgyzstan, this week in the AGU Journal of Geophysical Research: Earth Surface (open access here). The recovery of subglacial gold deposits at Kumtor Mine has necessitated the excavation of an open ice pit into the Lysii and Davidov Glaciers. In addition to excavating glacier overburden, a major geotechnical challenge at Kumtor Mine has been managing the flow of both glaciers. In their study, Jamieson et al. (2015) use a comprehensive set of high resolution satellite images to document recent artificial surges induced in both these glaciers in response to mining activities. Photos released by Radio Free Europe in 2013 suggest that these artificial surges quite adversely impacted mining operations (Figure 1).

Kumtor_glacier_damage

Figure 1 – Infrastructure damage resulting from what is now a confirmed glacier advance at the Kumtor Mine in Kyrgyzstan (originally discussed in this earlier post)

The dumping of waste rock on both glaciers, in which waste rock piles reached up to 180 m thick, substantially increased the driving stress of the ice beneath. Given that ice deformation is related to driving stress to an exponent of three, and potentially higher exponents at higher driving stresses, this resulted in a significant increase in ice velocity. Jamieson et al. (2015) estimate that surface velocities of the Davidov Glacier increased from a few meters per year to several hundred meters per year within a decade. During this time, the Lysii and Davidov Glaciers advanced by 1.2 and 3.2 km, respectively, with Davidov Glacier terminus advance reaching 350 meters per year in c. 2012 (Figure “7”).

Jamieson1

This study is probably the most textbook-comprehensive documentation of a human-induced artificial glacier surge to date, and will provide a great resource for my students to debate the sometimes fine line between geotechnical misstep and natural hazard!

Reference

(Jamieson, S., M. Ewertowski and D. Evans. 2015. Rapid advance of two mountain glaciers in response to mine-related debris loading. Journal of Geophysical Research: Earth Surface. 120: doi:10.1002/2015JF003504.

Tags: , , , , ,

Greenland Ice Sheet “Thermal-Viscous Collapse”

Posted by William Colgan on July 17, 2015
Climate Change, New Research / No Comments

We have a new study in the AGU open access journal Earth’s Future this month, which introduces the notion of thermal-viscous collapse of the Greenland ice sheet1. While people tend to think of ice as a solid, it is actually a non-Newtonian fluid, because it deforms and flows over longer time-scales. Of the many strange material properties of ice, the non-linear temperature dependence of its viscosity is especially notable; ice at 0 °C deforms almost ten times more than ice at -10 °C at the same stress. This temperature-dependent viscosity makes ice flow very sensitive to ice temperature. We know that the extra meltwater now being produced at the surface of the Greenland ice sheet, relative to 50 or 100 years ago, contains tremendous latent heat energy. So, in the study, we set out to see if the latent heat in future extra meltwater might have a significant impact on future ice sheet form and flow.

We first developed a conceptual model of what we called “thermal-viscous collapse”, which we define as the enhanced ice flow resulting from warming ice temperatures and subsequently softer ice viscosities. We decided there were three key processes necessary for initiating a thermal-viscous collapse: (1) sufficient energy available in future meltwater runoff, (2) routing of that extra meltwater to the ice-bed interface, and (3) efficient transfer of latent energy from meltwater to the ice. Drawing on previous model projections and observational process studies, and admittedly an injection of explicit speculation, we concluded that it is plausible to warm the deepest 15 % of the Greenland ice sheet, where the majority of deformation occurs, from characteristic Holocene temperatures to the melting-point in the next four centuries.

Figure_2

Figure 1 – Three key elements of thermal-viscous Greenland ice sheet collapse: (1) Sufficient energy available in projected Greenland meltwater runoff, (2) Routing of a fraction of meltwater to the interior ice-bed interface, and (3) Efficient energy transfer from meltwater to ice. This cross-sectional profile reflects mean observed Greenland ice surface and bedrock elevations between 74.1 and 76.4°N. Dashed lines illustrate stylized marine and land glacier termini.

We then used a simple (first-order Navier-Stokes) model of ice flow to simulate the effect of this warming and softening on the ice sheet over the next five centuries. We used a Monte Carlo approach, whereby we ran fifty simulations in which multiple key parameters were varied within their associated uncertainty. As may be expected, warming the deepest 15 % of the ice sheet by 8.8 °C, from characteristic Holocene temperatures to the melting-point, had a significant influence on ice sheet form and flow. Due to softer ice viscosities, the mean ice sheet surface velocity increased three fold, from 43 ± 4 m/yr to 126 ± 17 m/yr, resulting in an ice dynamic drawdown of the ice sheet, causing a 5 ± 2 % ice sheet volume reduction within 500 years. This is equivalent to a global mean sea-level rise contribution of 33 ± 18 cm (or just over one US foot). Of course, the vast majority of the sea level rise associated with thermal-viscous collapse would occur over subsequent millennia.

Figure_11

Figure 2 – Probability density time series of ensemble spread of 50 simulations in prescribed ice temperature (a), mean surface ice velocity (b), and ice volume (c), over a 200-year spin-up to transient equilibrium, and the subsequent 500-year combined transient forcing and spin-down period.

Perhaps a caveat or two: Just like simulating a marine instability induced collapse of the West Antarctic ice sheet, our simulation of a thermal-viscous collapse of the Greenland ice sheet is an entirely hypothetical end-member scenario. It is admittedly difficult to interpret end-member assessments when their probability of occurrence is unknown. In our case, we did not attempt to constrain the probability of a thermal-viscous collapse of the Greenland ice sheet, we merely demonstrated that initiating a thermal-viscous collapse appears plausible within four centuries, and assessed the associated sea-level rise contribution. Additionally, it may be debatable whether the combination of crevasses and reverse drainage can indeed route meltwater throughout the ice sheet interior, but I suppose that is a debate worth having!

Reference

1Colgan, W., A. Sommers, H. Rajaram, W. Abdalati, and J. Frahm. 2015. Considering thermal-viscous collapse of the Greenland ice sheet. Earth’s Future. 3. doi:10.1002/2015EF000301.

Tags: , , , , , , , ,

Hybrid Gravimetry and Altimetry Mass Balance

Posted by William Colgan on July 07, 2015
Communicating Science, New Research, Sea Level Rise / No Comments

We have a new study in this month’s Remote Sensing of Environment, which examines satellite-derived glacier mass balance in Greenland and the Canadian Arctic1. Satellites are generally used to assess glacier mass balance through changes in volume (via satellite altimetry) or changes in mass (via satellite gravimetry). While satellite altimetry observes volume changes at relatively high spatial resolution, it necessitates the forward modeling of firn processes to convert volume changes into mass changes. Conversely, the cryosphere-attributed mass changes observed by satellite gravimetry, while very accurate in absolute terms, have relatively low spatial resolution. In this study, we sought to combine the complementary strengths of both approaches. Using an iterative inversion process that was essentially sequential guess-and-check with a supercomputer, we refined gravimetry-derived observations of cryosphere-attributed mass changes to the relatively high spatial resolution of altimetry-derived volume changes. This gave us a 26 km spatial resolution mass balance field across Greenland and the Canadian Arctic that was simultaneously consistent with: (1) glacier and ice-sheet extent derived from optical imagery, (2) cryospheric-attributed mass trends derived from gravimetry, and (3) ice surface elevation changes derived from altimetry. We have made digital versions of this product available in the supplementary material associated with the publication.

Figure_1

Figure 1 – Observational data inputs to our inversion algorithm. A: Cryosphere-attributed mass changes observed by gravimetry. B: Land ice extent observed by optical imagery. C: Ice surface elevation changes observed by altimetry.

To make sure our inferred mass balance field was reasonable, we evaluated it against all in situ point mass balance observations we could find. Statistically, the validation was great, yielding an RMSE of 15 cm/a between the inversion product and in situ measurements. Practically, however, this apparent agreement largely stems from the fact that we could only find forty in situ point mass balance observations against which to compare. Evaluating our area-aggregated sector-scale mass balance estimates against all previously published sector-scale estimates provides a more meaningful validation. This suggests the magnitude and spatial distribution of inferred mass balance is reasonable, but highlights that the community needs more in situ point observations of mass balance, especially from peripheral glaciers and regions of high dynamic drawdown in Greenland. (For the glaciology hardcores I will note that “mass balance” is distinct from “surface mass balance”, in that the former measurement also includes the ice dynamic portion of mass change.)

Figure_11_corrected

Figure 2 – A comparison of similar sector scale mass balance estimates and associated uncertainties across Greenland and the Canadian Arctic. Dashed lines denote estimates that pertain to the Greenland ice sheet proper (i.e. exclusive of peripheral glaciers). Jacob et al. (2012) estimates pertain to Canada, while Sasgen et al. (2012) estimates pertain to Greenland.

This new inversion mass balance product, which we are calling “HIGA” (Hybrid glacier Inventory, Gravimetry and Altimetry), suggests that between 2003 to 2009 Greenland lost 292 ± 78 Gt/yr of ice and the Canadian Arctic lost  42 ± 11 Gt/yr of ice. While the majority of Greenland’s ice loss was associated with the ice sheet proper (212 ± 67 Gt/yr), peripheral glaciers and ice caps, which comprise < 5 % of Greenland’s ice-covered area, produced ~ 15 % of Greenland mass loss (38 ± 11 Gt/yr). A good reminder that ice loss from “Greenland” is not synonymous with ice loss from the “Greenland ice sheet”. Differencing our tri-constrained mass balance product from a simulated surface mass balance field allowed us to assess the ice dynamic component of mass balance (technically termed the “horizontal divergence of ice flux”). This residual ice dynamic field infers flux divergence (or submergent ice flow) in the ice sheet accumulation area and at tidewater margins, and flux convergence (or emergent ice flow) in land-terminating ablation areas. This is consistent with continuum mechanics theory, and really highlights the difference in ice dynamics between the ice sheet’s east and west margins.

Figure_13

Figure 3 – Spatially partitioning the glacier continuity equation in surface and ice dynamic components. A: Transient glacier and ice sheet mass balance. B: Simulated surface mass balance. C: Residual ice dynamic (or horizontal divergence of ice flux) term. The ∇Q color scale is reversed to maintain blue shading for mass gain and red shading for mass loss in all subplots. Color scales saturate at minimum and maximum values. Black contours denote zero.

As with some scientific publications, this one has a bit of a backstory. In this case, we submitted a preliminary version of the study to The Cryosphere in December 2013. After undergoing three rounds of review at The Cryosphere, the first one of which is archived in perpetuity here, it was rejected, primarily for insufficient treatment of the uncertainty associated with firn compaction. Coincidentally, on the same day I received The Cryosphere rejection letter, I received a letter from the European Space Agency (ESA) granting funding for a follow-up study. A mixed day on email indeed! After substantial retooling, including a discussion section dedicated to firn compaction and the most conservative error bounds conceivable, we were happy to see this GRACE-ICESat study funded by NASA and the Danish Council for Independent Research appear in Remote Sensing of Environment. The editors at both journals, however, were very helpful in moving us forward. Our ESA-funded GRACE-CryoSat product development is now ongoing, but a sneak peek is below.

ESA_partition

Figure 4 – Same as Figure 3, except using a 5 km resolution GRACE-CryoSat inversion product instead of a 26 km resolution GRACE-ICESat inversion product. Colorbars are different in shading, but identical in magnitude.

Reference

1W. Colgan, W. Abdalati, M. Citterio, B. Csatho, X. Fettweis, S. Luthcke, G. Moholdt, S. Simonsen, M. Stober. 2015. Hybrid glacier Inventory, Gravimetry and Altimetry (HIGA) mass balance product for Greenland and the Canadian Arctic. Remote Sensing of Environment. 168: 24-39.

Tags: , , , , , ,

New Estimate of Ice Sheet Runoff at Isua Site

Posted by William Colgan on April 14, 2015
Applied Glaciology, New Research / No Comments

My colleague Lukas Arenson and I have a paper in the Proceedings of Mine Water Solutions in Extreme Environments this month, which uses the Isua site in Southwest Greenland as a case study for extreme runoff in proglacial environments (Arenson and Colgan, 2015). The recently approved Isua mine will be an open pit mine intersecting the ice sheet, with ice pit walls around about half the pit, to access what is presently a subglacial iron deposit (site overview here). Using a Monte Carlo approach, we estimate a 95 % (or two sigma) upper confidence limit of 2.8·109 L/day of ice sheet runoff potentially reaching the Isua site in July and August. While this potential inflow rate, equivalent to 44 t/s, is relatively large in the context of conventional mine water management, it is relatively small in the context of contemporary Greenland ice loss due to climate change, which is approximately 8,300 t/s when averaged over a year (Andersen et al., 2015).

Isua_meltwater_runoff_estimate

Minimum and maximum plausible supraglacial ice sheet catchments associated with the Isua site. Shading denotes mean annual meltwater runoff over the 2004 to 2013. Background image source is Landsat 8 (source: Arenson and Colgan, 2015).

To place our estimate in context, London Mining Plc, the initial developer of the Isua site, presented a pre-feasibility study water balance in which ice sheet runoff into the pit was estimated as 7.8·106 m3/year (London Mining, 2011). Assuming a 60-day melt season, this is equivalent to an average site inflow of 1.3·108 L/day. Our estimate is therefore 22 times greater than the design estimate. There are many potential sources of uncertainty when assessing ice sheet runoff, including model uncertainty and climatic variability, but by far the biggest source of uncertainty is delineating the ice sheet catchment draining to a specific portion of the ice sheet margin. Regardless of whether 108 or 109 L/day of meltwater is flowing into the Isua site, it will certainly be a challenging operating environment, and will require some very adaptive engineering to minimize site contact water!

Isua_SNC_Budget

Proponent water budget for the Isua Mine (source: London Mining, 2011).

Isua_2011 173

Oblique aerial photograph looking west from the Greenland ice sheet across the Isua site in 2011. Deeply incised supraglacial meltwater channels are visible draining towards the margin. (source: Lukas Arenson)

References

Andersen et al., 2015. Basin-scale partitioning of Greenland ice sheet mass balance components (2007–2011). Earth and Planetary Science Letters 409: 89-95.

Arenson and Colgan. 2015. Water management challenges associated with mining projects in Greenland. Proceedings of Mine Water Solutions in Extreme Environments. 533-543.

London Mining PLC. 2011. Isua iron ore project: Isua 15 Mtpa scoping study report.

Tags: , , , , ,

Greenland Piteraqs and Expedition Insurance

Posted by William Colgan on April 07, 2015
Commentary, Communicating Science / 3 Comments

As the 2015 Greenland expedition season gets underway, I want to comment on the insurance overlap between research and sport expeditions on the ice sheet.

Greenland can be a very windy place. The world’s fourth fastest observed wind speed, 333 km/h, was clocked at Thule, Northwest Greenland, in a March 1972 storm1. The “piteraq” (or “ambush”) wind is an especially strong type of wind, unique to Greenland, which occurs when katabatic winds align with the regional geostrophic wind field. During piteraq events, relatively cold and dense air not only flows down from the top of the ice sheet under gravity, but is also sucked down by low atmospheric pressure at the coast2. Piteraqs are strongest around the ice sheet periphery, especially in Southeast Greenland, adjacent to the Icelandic Low.

In April 2013, a few colleagues and I were doing fieldwork on the ice sheet at KAN_U in Southwest Greenland, when a piteraq struck Southeast Greenland. Our TAS_U weather station there recorded sustained winds of just over 150 km/hr during the piteraq3. Since 2007, TAS_U has recorded a number of piteraqs, some have even been strong enough to knock over or damage the station. The April 2013 event, which left the TAS_U station standing, would probably not have been noteworthy if it had not claimed the life of Philip Goodeve-Docker, who was just two days into a three-man sport expedition to cross the ice sheet from Isortoq to Kangerlussuaq4.

Piteraq_Dirk_Graph

Mean hourly wind speeds at KAN_U and TAS_U weather stations during the April 2013 piteraq event. Inset: Locations of KAN and TAS transects, as well as other transects, in South Greenland. (source: van As et al., 2014)

The number of annually permitted Greenland sport expeditions is perhaps surprisingly high. An information request to Greenland Government by my colleague, Dirk van As, found that, during the 2010 to 2012 seasons, approximately 78 teams annually undertook sport expeditions in Greenland (including coastal kayaking), of which approximately 24 teams per year were dedicated ice sheet crossings5. Assuming a sport expedition team size of four people, that is approximately 100 individuals per year crossing the ice sheet, mostly along the 67th parallel (the “Isortoq-Kangerlussuaq highway”). All of these sport individuals are obliged to purchase search and rescue (SAR) insurance. While some nationally-funded research expeditions (basically just Danish and American) are permitted to “self-insure”, all other research expeditions have to buy into the same SAR insurance. Occasionally, and strictly speaking, even just specific members of a research expedition, such as persons not employed within the sponsoring nation, may be obliged to purchase their own SAR.

Sport_Route

Map of permitted and non-permitted expedition areas in Greenland, as well as the approximate location of the Isortoq-Kangerlussuaq sport route. (source: Greenland Government)

In 2011, I received a SAR quote of 6200 DKK (900 USD) to cover a non-Danish member of a Danish expedition for just eight days. I shudder to think what some colleagues must pay to insure a six person research expedition for a month. At the time, the round-trip helicopter flight to our ice sheet site cost only about ten times our quote premium, meaning that in a zero profit world the underwriters would be recusing approximately 10 % of policyholders. Turns out, that is not far off the truth for sport expeditions. Of the 234 sport expeditions initiated in Greenland between 2010 and 2012, sixteen ended in emergency evacuation5. That is 7 % of all Greenland sport expeditions. The ice sheet teams were evidently better prepared with a lower, but still non-trivial, evacuation rate of 3 %.

Insurance_caveat

As Greenland SAR insurance treats research and sport expeditions as functionally equivalent, both are technically required to bring more daily calories than even an Olympic swimmer might consume. The above 6.6a clause obliges a 21 day expedition to bring the equivalent of 30 kg of peanut butter per person. (source: Insurance for journeys and expeditions in Greenland policy drawn up in cooperation with the Danish Polar Center conditions no. 101B)

For insurance purposes, both sport and research expeditions are effectively regarded as having the same safety margin. In fact, research expeditions, often delivered by aircraft with >1000 kg of cargo per person, have an inherently higher safety margin than skiers pulling a <200 kg sled. I would love to have the comparable evacuation statistic for research expeditions. We have such an information request pending with Greenland Government, but I will go out on a limb and guess that the research expedition evacuation rate is not nil, but an order of magnitude lower than the sport expedition evacuation. This asymmetry in evacuation risk means that when predominately publicly-funded research expeditions buy SAR insurance, they are effectively subsidizing the SAR costs of predominately privately-funded sport expeditions. To make an analogy, auto insurance rates usually vary between motorcycles and mini-vans. In lieu of different insurance premiums for research and sport expeditions, perhaps the safety of sport expeditions could at least be further optimized by drawing on ice sheet research. (Not forgetting that reducing SAR calls is not just about cost, but also about the preservation of life!)

Expedition_resource_level

Vastly differing resource levels: Our 2013 research expedition being delivered by LC-130 with two of three pallets (left: Charalampos (Babis) Charalampidis) and a 2008 sport expedition arriving at our West Greenland campsite (right).

This brings us back to piteraqs, which should probably rank at the top of sport expedition hazards, above the more often cited trio of “cold, crevasses and polar bears”. For example, if research suggests that the ice sheet flank is windier in the Southeast than the Southwest, east to west crossings (Isortoq to Kangerlussuaq) would appear to provide sport teams more ample opportunity to wait for an appropriate weather window before setting upon the relatively piteraq prone Southeast flank. Right now, however, the majority of crossings (61 %) are in the opposite direction (west to east), with sport teams arriving in “piteraq alley” with no possibility for retreat5. Danish Meteorological Institute forecasts already include piteraq warnings for Greenland coastal towns. But while research has made piteraqs eminently predictable from 48 hours away, the Goodeve-Docker expedition was jeopardized within 48 hours of departing Isortoq. Evidently, more applied publications and outreach, to better communicate such research insight directly to teams, is needed.

So, those are some thoughts on how sport and research expeditions are linked by common SAR insurance, perhaps arguably to the detriment of research expeditions, and how the piteraq hazard might be mitigated for sport expeditions. Unfortunately, regional climate model simulations suggest that wind speeds around the ice sheet periphery will increase under climate change6, meaning that there will likely be more piteraqs in everyone’s future.

I should probably make explicitly clear that these are my own thoughts, and not those of my employing institution.

1Stansfield, J. 1972. The severe Arctic storm of 8–9 March 1972 at Thule
Air Force Base, Greenland. Weatherwise. 25: 228–233.

2Oltmanns, M., et al. 2014. Strong Downslope Wind Events in Ammassalik, Southeast Greenland. Journal of Climate. 27: 977–993.

3van As, D., et al. 2014. Katabatic winds and piteraq storms: observations from the Greenland ice sheet. Geological Survey of Denmark and Greenland Bulletin. 31: 83-86.

4Edmonds, R. 1 May 2014. Explorer Philip Goodeve-Docker freezes to death on second day of trek across Greenland. London Evening Standard.

5Greenland Government. 2013. Statistik fra Administration af rejseaktivitet I Grønland. 6 pages.

6Gorter, W. et al. 2013. Present and future near-surface wind climate of Greenland from high resolution regional climate modeling. Climate Dynamics. 42: 1595-1611.

Tags: , , , , , , ,

Greenland’s “Recent Mass Loss” Underestimated?

Posted by William Colgan on March 09, 2015
Climate Change, Communicating Science, New Research / No Comments

There are a variety of methods used to estimate the present rate of mass loss from the Greenland ice sheet, including satellite altimetry, satellite gravimetry and input-output assessments. All of these methods generally agree that since 2005 the ice sheet has been losing c. 250 Gt/yr of mass (equivalent to 8000 tonnes of ice per second). Partitioning this mass loss into climatic surface balance (i.e. snowfall minus runoff) and ice dynamic (i.e. iceberg calving) contributions is a little more challenging. Partitioning recent mass loss into surface balance or ice dynamic components requires us to look at the changes in each of these terms since a period during which the ice sheet was approximately in equilibrium. Conventionally, the ice sheet is assumed to have been in equilibrium during the 1961-1990 so-called “reference period”.1

Figure_6_mass_balance_monitoring

The three main methods of measuring present-day ice sheet mass balance: (1) snowfall input minus iceberg output, (2) changes in elevation using satellite altimetry, and (3) changes in gravity using satellite gravimetry (from Alison et al., 2014)5.

Our recently published study in the Annals of Glaciology takes a hard look at the mass balance of the high elevation interior of the Greenland ice sheet during the reference period2. We difference the ice flowing out of a high elevation perimeter from the snow falling within it, and conclude that the ice sheet was likely gaining at least 20 Gt/yr of mass during the reference period. This implies that rather than ice sheet mass balance decreasing from c. 0 Gt/yr (or “equilibrium”) during reference period to c. -250 Gt/yr since 2005, it may have actually decreased from c. +20 Gt/yr of subtle mass gain during reference period to c. -250 Gt/yr since 2005. This interpretation would mean the “recent” (pre-1990 to post-2005) mass loss of the ice sheet is actually 7 % greater than might conventionally be assumed (270 vs. 250 Gt/yr). Seven percent more recent mass loss than conventionally assumed might not sound like much, but it becomes important when we try to partition mass loss in surface balance or ice dynamics components.

reference_period

Illustration of how a subtle mass gain during reference period (1961-1990) , when the Greenland ice sheet is conventionally assumed to have been in approximate equilibrium, can influence the magnitude of “recent mass loss” used to partition surface balance and ice dynamics components of mass loss.

We also assessed whether surface balance or ice dynamics were responsible for subtle reference period mass gain. We concluded it was more likely long term ice dynamics, resulting from the downward advection through the ice sheet of the transition between relatively soft Wisconsin ice (deposited > 10.8 KaBP) and relatively hard Holocene ice (deposited < 10.8 KaBP). In 1985, Niels Reeh proposed that subtly increasing effective ice viscosity was resulting in cm-scale ice sheet thickening3. Increased iceberg calving, or enhanced ice dynamics, are conventionally assumed to be responsible for c. 100 Gt/yr of recent mass loss4. Since we conclude ice dynamics were likely responsible for subtle reference period mass gain, we are implying that mass loss due to ice dynamics may actually be c. 20 Gt/yr greater than conventionally assumed, or c. 120 Gt/yr rather than c. 100 Gt/yr since 2005. Without invoking any departures from the conventional view of changes in surface balance since reference period, this infers 20 % more mass loss due to ice dynamics since reference period. This becomes important if diagnostic ice sheet model simulations are calibrated to underestimated recent ice dynamic mass loss, which may subsequently bias prognostic model simulations to similarly underestimate future ice dynamic mass loss.

Wisconsin_Tiff

An ice sheet composed of relatively hard Holocene ice is theoretically c. 15 % thicker than one composed of relative soft Wisconsin ice. Today’s ongoing transition from Wisconsin to Holocene ice within the Greenland ice sheet should theoretically result in cm-scale transient thickening (after Reeh, 1985).

Pondering how a millennial-scale shift in ice dynamics may be responsible for subtle mass gain during the 1961-1990 period, and how that ultimately influences our understanding of present-day mass loss partition, is definitely a rather nuanced topic. I am guessing there are not many non-scientists still reading at this point. Spread over the high elevation ice sheet interior, a 20 Gt/yr mass gain is equivalent to a thickening rate of just 2 cm/yr, which is within the uncertainty of virtually all mass balance observation methods, including in situ point measurements. I suppose the thrust of our study is to be receptive to the idea that millennial scale ice dynamics may be contributing to a subtle ice sheet thickening that underlies both past and present ice sheet mass balance, and to appreciate the non-trivial uncertainty in partitioning recent mass loss into surface balance and ice dynamic components that stems from the particular reference period mass balance assumption that is invoked.

1Van den Broeke, M., J. Bamber, J. Ettema, E. Rignot, E. Schrama, W. van de Berg, E. van Meijgaard, I. Velicogna and B. Wouters. 2009. Partitioning Recent Greenland Mass Loss. Science. 326: 984-986.

2Colgan, W., J. Box, M. Andersen, X. Fettweis, B. Csatho, R. Fausto, D. van As and J. Wahr. 2015. Greenland high-elevation mass balance: inference and implication of reference period (1961-90) imbalance. Annals of Glaciology. 56: doi:10.3189/2015AoG70A967.

3Reeh, N. 1985. Was the Greenland ice sheet thinner in the late Wisconsinan than now?
Nature. 317: 797-799.

4Enderlin, E., I. Howat, S. Jeong, M. Noh, J. van Angelen and M. van den Broeke. 2014. An improved mass budget for the Greenland ice sheet. Geophysical Research Letters. 41: doi:10.1002/2013GL059010.

5Alison, I., W. Colgan, M. King and F. Paul. 2014. Ice Sheets, Glaciers, and Sea Level Rise. Snow and Ice-Related Hazards, Risks and Disasters. W. Haeberli and C. Whiteman. Elsevier. 713-747.

Tags: , , , , , , , ,

Greenland data rescue: An appeal

Posted by William Colgan on November 24, 2014
Communicating Science, Glaciology History, New Research / No Comments

As described in this month’s newsletter No 7, the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) is nearing completion of its comprehensive database of surface mass budget observations from the Greenland ice sheet melt area and peripheral glaciers. We now have just over 2400 unique observations spanning from the 1938 Freja Glacier expedition to the present. Approximately half these observations have never been published. These historic measurements were fragmented across studies, most of which were pre-digital or unpublished, effectively making this highly valuable data inaccessible to the global research community. Despite our best efforts, however, we are still missing data from a handful of known expeditions. For example, does someone you know perhaps have a copy of Alfred Wegener’s 1930 Qaamarujuk Glacier observations? There is a chance we might even be unaware of some expeditions, especially recent private sector prospecting work. Please get in touch with Horst Machguth (homac@byg.dtu.dk) of the www.promice.dk team if you can help us out with this community data assimilation project!

Colgan, W., H. Machguth and A. Ahlstrom. 2014. Data Rescue: Greenland Surface Mass Budget Database. PROMICE newsletter No 7. Ed. S. Andersen and H. Pedersen.

database_map

Map of the location, with temporal description, of the Greenland ice sheet melt area and local glacier surface mass budget observations presently contained in the database. The grey sites are the missing data (from a manuscript in preparation).

Tags: , , , , ,

Greenland ice loss: 8300 tonnes per second

Posted by William Colgan on November 19, 2014
Communicating Science, New Research, Sea Level Rise / 1 Comment

We have a new study coming out in Earth and Planetary Science Letters that looks into the mass loss of the Greenland ice sheet (Andersen et al., 2015). We used the “input-output” approach, whereby an estimated iceberg production rate is differenced from an estimated snow accumulation rate. The input-output approach we used was slightly different from previous studies (such as Rignot et al., 2008 or Enderlin et al., 2014) because the ice sheet perimeter across which we observed ice flow (or the “flux gate”) was relatively far inland. That meant we had to make a different assumption about the vertical velocity profile at the flux gate, as well as account for changes in ice volume between the flux gate and the tidewater glacier grounding lines. We also used a new combination of satellite-derived ice surface velocity product, airborne radar-derived ice thickness observations, and surface mass balance simulations. Despite all this, our mass loss estimate agrees pretty well with previous studies!

The numbers are pretty striking: We estimate that between 2007 and 2011 the Greenland ice sheet alone, not counting all the peripheral glaciers in Greenland, lost 262 Gt of ice per year. That works out to about 8300 tonnes per second! That means the Greenland ice sheet probably weighs 250,000 tonnes less than when you started reading this blog post. No wonder we can measure its mass loss by gravitational anomalies! The ice sheet is currently losing mass via both surface runoff (the difference between accumulation and melt) and ice dynamics (the production of icebergs). We estimate that runoff comprised about 61 % of the ice sheet’s mass loss, or about 5000 tonnes per second, with iceberg production comprising the remaining 3300 tonnes per second of mass loss. Some big numbers that confirm the Greenland ice sheet is presently raising global mean sea level by about 0.73 mm per year.

Enderlin, E., I. Howat, S. Jeong, M. Noh, J. van Angelen & M. van den Broeke. 2014. An improved mass budget for the Greenland ice sheet. Geophysical Research Letters. 41: doi:10.1002/2013GL059010.

Rignot, E., J. Box, E. Burgess & E. Hanna. 2008. Mass balance of the Greenland ice sheet from 1958 to 2007. Geophysical Research Letters. 35: doi:10.1029/2008GL035417.

Andersen, M., L. Stenseng, H. Skourup, W. Colgan, S. Khan, S. Kristensen, S. Andersen, J. Box, A. Ahlstrøm, X. Fettweis & R. Forsberg. 2015. Basin-scale partitioning of Greenland ice sheet mass balance components (2007–2011). Earth and Planetary Science Letters. 409: 89–95. doi:10.1016/j.epsl.2014.10.015.

Greenland_InputOutput

Diagram showing differences in methodology between our study (TOP) and previous studies (BOTTOM) in converted estimated ice flux (F) into estimated iceberg production (D). We adopt a higher elevation “flux gate”, which necessitates accounting for downstream changes in ice volume (∆S), as well as making a different assumption about the vertical velocity profile at the flux gate. We also use different velocity and ice thickness observations, and a different surface mass balance (SMB) model (from Andersen et al., 2015).

Tags: , , , ,

Sixty Years of Snow Runways

Posted by William Colgan on November 14, 2014
Cold War Science, Glaciology History / 3 Comments

About sixty years ago, in September 1955, the US Army Corps of Engineers conducted the first test landings of wheeled military transport planes on a prepared snow runway at Site II, Greenland. The 3000 meter (10,000 foot) snow runway was prepared by repeatedly pulverizing and compressing the ice sheet’s snow surface with low ground pressure tractors. Driving the tractors from Camp TUTO to Site II, high in the ice sheet interior, took several days.

Eight successful landings with a C-47 Skytrain, led to six successful landings with a C-54 Skymaster, and finally seven successful landings with a C-124 Globemaster. Landing the pug-nosed C-124, which has an empty weight of 45,000 kg (100,000 lbs), on prepared snow runways formed the backbone of ice sheet logistics in both Greenland and Antarctica throughout the International Geophysical Year (1957-1958). The slightly more nimble ski-equipped LC-130 Hercules, now a symbol of polar research, was not tested in Northwest Greenland for six more years.

So, perhaps a nod to the 60th anniversary of snow runways, without which ice sheet camps and their precious ice cores and other glaciological data would not be possible!

Correction: In an earlier post version I said the first C-124 usage of a snow runway was in September 1954. In fact, the snow runway technique was developed in September 1954, but the first C-124 usage of a snow runway was not until September of 1955. The 59.5th anniversary of transport planes and snow runways?

Polar Ice Coring and IGY 1957-58: An Interview with Dr. Anthony J. “Tony” Gow.

(skimmed from my upcoming Cold War science project.)

 

C124_icecap

A wheeled C-124 Globemaster unloading on a snow runway at McMurdo Station, Antarctica, to deliver a smaller ski-equipped plane in 1956 (photo by Jim Waldron; http://icecores.org)

C130_icecap

A ski-equipped C130 Hercules taxing at Dye-2, Greenland, after dropping of our field party for there weeks in the spring of 2013. (personal photo!)

Tags: , , , , , ,

New Book: Snow and Ice-Related Hazards

Posted by William Colgan on October 11, 2014
Communicating Science, New Research / No Comments

A new textbook, “Snow and Ice-Related Hazards, Risks, and Disasters”, is scheduled for release October 15 as part of Elsevier’s Hazards and Disasters series. With 80+ authors and 800+ pages, the textbook covers a range of diverse cryospheric hazards, from permafrost degradation to avalanches, as well as a number of glacier hazards, including chapters on: glacier surges, glacier outburst floods, glacier loss and slope stability, glacierized volcanoes, and glacier-derived sea level rise. A chapter on “Radioactive Waste Under Conditions of Future Ice Ages” even sounds mildly intriguing! The target audience is applied earth and environmental scientists. The pre-order purchase price is currently c. 100 USD via elsevier.com. As an overly keen contributing author, I have of course already ordered my copy!

Haeberli, W., and C. Whiteman (ed). 2014. Snow and Ice-Related Hazards, Risks, and Disasters. Elsevier. ISBN: 9780123948496.

snow_ice_related_hazards_textbook_cover

Cover and spine of “Snow and Ice-Related Hazards, Risks, and Disasters” from Elsevier (ISBN: 9780123948496). (from W. Haeberli)