uu.seUppsala University Publications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Climatology and firn processes in the lower accumulation area of the Greenland ice sheet
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Geological Survey of Denmark and Greenland (GEUS). (Ice, Climate and Environment)ORCID iD: 0000-0003-0853-697X
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Greenland ice sheet is the largest Northern Hemisphere store of fresh water, and it is responding rapidly to the warming climate. In situ observations document the changing ice sheet properties in the lower accumulation area, Southwest Greenland. Firn densities from 1840 meters above sea level retrieved in May 2012 revealed the existence of a 5.5-meter-thick, near-surface ice layer in response to the recent increased melt and refreezing in firn. As a consequence, vertical meltwater percolation in the extreme summer 2012 was inefficient, resulting in surface runoff. Meltwater percolated and refroze at six meters depth only after the end of the melt season. This prolonged autumn refreezing under the newly accumulated snowpack resulted in unprecedented firn warming with temperature at ten meters depth increased by more than four degrees Celsius. Simulations confirm that meltwater reached nine meters depth at most. The refrozen meltwater was estimated at 0.23 meters water equivalent, amounting to 25 % of the total 2012 ablation.

A surface energy balance model was used to evaluate the seasonal and interannual variability of all surface energy fluxes at that elevation in the years 2009 to 2013. Due to the meltwater presence at the surface in 2012, the summer-averaged albedo was significantly reduced (0.71 in 2012; typically 0.78). A sensitivity analysis revealed that 71 % of the subsequent additional solar radiation in 2012 was used for melt, corresponding to 36 % of the total 2012 surface lowering. This interplay between melt and firn properties highlights that the lower accumulation area of the Greenland ice sheet will be responding rapidly in a warming climate.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 81 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1372
Keyword [en]
climate change, Greenland ice sheet, accumulation area, automatic weather stations, surface energy balance, melt–albedo feedback, surface mass budget, snow, firn, meltwater, percolation, refreezing, runoff
National Category
Climate Research Environmental Sciences Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:uu:diva-284365ISBN: 978-91-554-9571-8 (print)OAI: oai:DiVA.org:uu-284365DiVA: diva2:920221
Public defence
2016-06-10, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:15 (English)
Opponent
Supervisors
Projects
Stability and Variations of Arctic Land Ice (SVALI)Programme for Monitoring of the Greenland Ice Sheet (PROMICE)Greenland Analogue Project (GAP)
Available from: 2016-05-20 Created: 2016-04-17 Last updated: 2016-06-15
List of papers
1. Automatic weather stations for basic and applied glaciological research
Open this publication in new window or tab >>Automatic weather stations for basic and applied glaciological research
Show others...
2015 (English)In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 33, 69-72 p.Article in journal (Refereed) Published
Abstract [en]

Since the early 1980s, the Geological Survey of Denmark and Greenland (GEUS) glaciology group has developed automatic weather stations (AWSs) and operated them on the Greenland ice sheet and on local glaciers to support glaciological research and monitoring projects (e.g. Olesen & Braithwaite 1989; Ahlstrøm et al. 2008). GEUS has also operated AWSs in connection with consultancy services in relation to mining and hydropower pre-feasibility studies (Colgan et al. 2015). Over the years, the design of the AWS has evolved, partly due to technological advances and partly due to lessons learned in the field. At the same time, we have kept the initial goal in focus: long-term, year-round accurate recording of ice ablation, snow depth and the physical parameters that determine the energy budget of glacierised surfaces. GEUS has an extensive record operating AWSs in the harsh Arctic environment of the diverse ablation areas of the Greenland ice sheet, glaciers and ice caps [...].

The GEUS AWS model in use now is a reliable tool that is adapted to the environmental and logistical conditions of polar regions. It has a proven record of more than 150 stationyears of deployment in Greenland since its introduction in 2007–2008, and a success rate of c. 90% defined as the fraction of months with more than 80% valid air-temperature measurements over the total deployment time of the 25 stations in the field. The rest of this paper focuses on the technical aspects of the GEUS AWS, and provides an overview of its design and capabilities.

Keyword
Greenland, AWS, automatic weather stations
National Category
Climate Research Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-280714 (URN)
Projects
Programme for Monitoring of the Greenland Ice Sheet (PROMICE)
Available from: 2016-03-14 Created: 2016-03-14 Last updated: 2017-11-30
2. Observed melt-season snowpack evolution on the Greenland ice sheet
Open this publication in new window or tab >>Observed melt-season snowpack evolution on the Greenland ice sheet
2015 (English)In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, no 33, 65-68 p.Article in journal (Refereed) Published
Abstract [en]

Due to recent warm and record-warm summers in Greenland (Nghiem et al. 2012), the melt of the ice-sheet surface and the subsequent runoff are increasing (Shepherd et al. 2012). About 84% of the mass loss from the Greenland ice sheet between 2009 and 2012 resulted from increased surface runoff (Enderlin et al. 2014). The largest melt occurs in the ablation zone, the low marginal area of the ice sheet (Van As et al. 2014), where melt exceeds wintertime accumulation and bare ice is thus exposed during each melt season. In the higher regions of the ice sheet (i.e. the accumulation area), melt is limited and the snow cover persists throughout the year. It is in the vast latter area that models struggle to calculate certain mass fluxes with accuracy. A better understanding of processes such as meltwater percolation and refreezing in snow and firn is crucial for more accurate Greenland ice sheet mass-budget estimates (Van Angelen et al. 2013).

In May 2012, the field campaign ‘Snow Processes in the Lower Accumulation Zone’ was organized by the Geological Survey of Denmark and Greenland (GEUS) at the KAN_U automatic weather station (67 degrees N, 47 degrees W; 1840 m above sea level), which delivers data to the Programme for Monitoring of the Greenland Ice Sheet (PROMICE; Van As et al. 2013) and is one of the few weather stations located in the lower accumulation area of Greenland. During the expedition, we installed thermistor strings, firn compaction monitors and a snowpack analyzer; we drilled firn cores, performed firn radar measurements, gathered meteorological data, dug snow pits and performed dye-tracing experiments. One important objective of the campaign was to understand the thermal variability in the snowpack during the melt season by monitoring with high-precision temperature probes [...].

Below, we present observations from the period 02 May to 23 July and interpret the atmosphere–surface interaction and its impact on the subsurface snow layers, with the goal to quantify refreezing in the Greenland accumulation area.

Keyword
snow, Greenland, ice sheet, percolation, refreezing
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-261333 (URN)000359477400016 ()
Projects
Stability and Variations of Arctic Land Ice (SVALI)Programme for Monitoring of the Greenland Ice Sheet (PROMICE)
Available from: 2015-09-01 Created: 2015-09-01 Last updated: 2017-12-04
3. Changing surface-atmosphere energy exchange and refreezing capacity of the lower accumulation area, West Greenland
Open this publication in new window or tab >>Changing surface-atmosphere energy exchange and refreezing capacity of the lower accumulation area, West Greenland
Show others...
2015 (English)In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 9, no 6, 2163-2181 p.Article in journal (Refereed) Published
Abstract [en]

We present 5 years (2009-2013) of automatic weather station measurements from the lower accumulation area (1840 m a.s.l. - above sea level) of the Greenland ice sheet in the Kangerlussuaq region. Here, the summers of 2010 and 2012 were both exceptionally warm, but only 2012 resulted in a strongly negative surface mass budget (SMB) and surface meltwater run-off. The observed run-off was due to a large ice fraction in the upper 10 m of firn that prevented meltwater from percolating to available pore volume below. Analysis reveals an anomalously low 2012 summer-averaged albedo of 0.71 (typically similar to 0.78), as meltwater was present at the ice sheet surface. Consequently, during the 2012 melt season, the ice sheet surface absorbed 28% (213 MJ m-2) more solar radiation than the average of all other years. A surface energy balance model is used to evaluate the seasonal and interannual variability of all surface energy fluxes. The model reproduces the observed melt rates as well as the SMB for each season. A sensitivity analysis reveals that 71% of the additional solar radiation in 2012 was used for melt, corresponding to 36% (0.64 m) of the 2012 surface lowering. The remaining 64% (1.14 m) of surface lowering resulted from high atmospheric temperatures, up to a + 2.6 degrees C daily average, indicating that 2012 would have been a negative SMB year at this site even without the melt-albedo feedback. Longer time series of SMB, regional temperature, and remotely sensed albedo (MODIS) show that 2012 was the first strongly negative SMB year, with the lowest albedo, at this elevation on record. The warm conditions of recent years have resulted in enhanced melt and reduction of the refreezing capacity in the lower accumulation area. If high temperatures continue, the current lower accumulation area will turn into a region with superimposed ice in coming years.

Keyword
energy balance, Greenland, ice sheet, melt, albedo, feedback, percolation, refreezing
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-275890 (URN)10.5194/tc-9-2163-2015 (DOI)000367523400010 ()
Projects
Stability and Variations of Arctic Land Ice (SVALI)Programme for Monitoring of the Greenland Ice Sheet (PROMICE)Greenland Analogue Project (GAP)
Available from: 2016-02-08 Created: 2016-02-08 Last updated: 2017-11-30
4. Greenland meltwater storage in firn limited by near-surface ice formation
Open this publication in new window or tab >>Greenland meltwater storage in firn limited by near-surface ice formation
Show others...
2016 (English)In: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 6, no 4, 390-393 p.Article in journal, Letter (Refereed) Published
Abstract [en]

Approximately half of Greenland's current annual mass loss is attributed to runoff from surface melt. At higher elevations, however, melt does not necessarily equal runoff, because meltwater can refreeze in the porous near-surface snow and firn. Two recent studies suggest that all or most of Greenland's firn pore space is available for meltwater storage, making the firn an important buffer against contribution to sea level rise for decades to come. Here, we employ in situ observations and historical legacy data to demonstrate that surface runoff begins to dominate over meltwater storage well before firn pore space has been completely filled. Our observations frame the recent exceptional melt summers in 2010 and 2012, revealing significant changes in firn structure at different elevations caused by successive intensive melt events. In the upper regions (more than similar to 1,900 m above sea level), firn has undergone substantial densification, while at lower elevations, where melt is most abundant, porous firn has lost most of its capability to retain meltwater. Here, the formation of near-surface ice layers renders deep pore space difficult to access, forcing meltwater to enter an efficient surface discharge system and intensifying ice sheet mass loss earlier than previously suggested.

Keyword
Greenland, ice sheet, refreezing, percolation, melt, firn
National Category
Climate Research
Identifiers
urn:nbn:se:uu:diva-280716 (URN)10.1038/nclimate2899 (DOI)000373060000016 ()
Projects
Stability and Variations of Arctic Land Ice (SVALI)Programme for Monitoring of the Greenland Ice Sheet (PROMICE)
Available from: 2016-03-14 Created: 2016-03-14 Last updated: 2017-11-30
5. Thermal tracing of retained meltwater in the lower accumulation area of the Southwestern Greenland ice sheet
Open this publication in new window or tab >>Thermal tracing of retained meltwater in the lower accumulation area of the Southwestern Greenland ice sheet
Show others...
2016 (English)In: Annals of Glaciology, ISSN 0260-3055, E-ISSN 1727-5644, Vol. 57, no 72, 1-10 p., 6000021Article in journal (Refereed) Published
Abstract [en]

We present in situ firn temperatures from the extreme 2012 melt season in the southwestern lower accumulation area of the Greenland ice sheet. The upper 2.5 m of snow and firn was temperate during the melt season, when vertical meltwater percolation was inefficient due to a c. 5.5 m thick ice layer underlying the temperate firn. Meltwater percolation and refreezing beneath 2.5 m depth only occurred after the melt season. Deviations from temperatures predicted by pure conductivity suggest that meltwater refroze in discrete bands at depths of 2.0–2.5, 5.0–6.0 and 8.0–9.0 m. While we find no indication of meltwater percolation below 9 m depth or complete filling of pore volume above, firn at 10 and 15 m depth was respectively 4.2–4.5 degrees C and 1.7 degrees C higher than in a conductivity-only simulation. Even though meltwater percolation in 2012 was inefficient, firn between 2 and 15 m depth the following winter was on average 4.7 degrees C warmer due to meltwater refreezing. Our observations also suggest that the 2012 firn conditions were preconditioned by two warm summers and ice layer formation in 2010 and 2011. Overall, firn temperatures during the years 2009–13 increased by 0.6 degrees C.

Keyword
Greenland ice sheet, accumulation area, firn, percolation, refreezing, superimposed ice
National Category
Climate Research
Identifiers
urn:nbn:se:uu:diva-284357 (URN)10.1017/aog.2016.2 (DOI)000385592800002 ()
Projects
Stability and Variations of Arctic Land Ice (SVALI)Programme for Monitiring of the Greenland Ice Sheet (PROMICE)Greenland Analogue Project (GAP)
Available from: 2016-04-17 Created: 2016-04-17 Last updated: 2017-11-30Bibliographically approved
6. Regional climate-model performance in Greenland firn derived from in situ observations
Open this publication in new window or tab >>Regional climate-model performance in Greenland firn derived from in situ observations
Show others...
2016 (English)In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 35, 75-78 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Copenahgen, Denmark: , 2016
Keyword
Regional climate model, RCM, Greenland ice sheet, firn, automatic weather stations, AWS
National Category
Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-284359 (URN)000383915800018 ()
Projects
Stability and Variations of Arctic Land Ice (SVALI)Programme for Monitoring of the Greenland Ice Sheet (PROMICE)Understanding and predicting non-linear change in the permeability of Greenland firn (RETAIN)
Available from: 2016-04-17 Created: 2016-04-17 Last updated: 2017-11-30Bibliographically approved

Open Access in DiVA

fulltext(5274 kB)261 downloads
File information
File name FULLTEXT01.pdfFile size 5274 kBChecksum SHA-512
5e7298f482a2776e8e3862cba3841e1f60a3d71a13a5bc653d430cc201b2b6d52ea63dbe17dcd4c4f877fafdb724b299eb0634e10739ad8fb90997073e11c173
Type fulltextMimetype application/pdf
Buy this publication >>

Authority records BETA

Charalampidis, Charalampos

Search in DiVA

By author/editor
Charalampidis, Charalampos
By organisation
LUVAL
Climate ResearchEnvironmental SciencesMeteorology and Atmospheric Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 261 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 2625 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf