Nanna Bjørnholt Karlsson

Nanna Bjørnholt Karlsson
Geological Survey of Denmark and Greenland · Department of Glaciology and Climate

Phd

About

105
Publications
24,325
Reads
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2,874
Citations
Introduction
As a glaciologist, my research is driven by a need to understand the processes that govern the response of ice sheets to climate change, in particular I am interested in the interaction between observations and models, and how this gap might be bridged. I work with ice-penetrating radar data from diverse places such as Greenland, Antarctica and Mars. I am interested in what the data can tell us about past and present conditions, and I use the data in conjunction with models to extract this information.
Additional affiliations
December 2023 - December 2028
Technical University of Denmark
Position
  • Professor (Full)
Description
  • Affiliated Professor at DTU Space
January 2016 - June 2017
Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research
Position
  • PostDoc Position
Description
  • Postdoc and project manager on the "Reconnaissance for the Oldest Ice" project, part of the European "Beyond EPICA - Oldest Ice" project.
November 2010 - December 2015
University of Copenhagen
Position
  • PostDoc Position
Description
  • Postdoc on the "Water under the Ice", ERC Advanced Grant with PI Dorthe Dahl-Jensen.

Publications

Publications (105)
Preprint
Full-text available
Radio-echo sounding (RES) has revealed an internal architecture within Antarctica’s ice sheets that records their depositional, deformational and melting histories. Crucially, spatially-widespread RES-imaged internal-reflecting horizons, tied to ice-core age-depth profiles, can be treated as isochrones that record the age-depth structure across the...
Article
Full-text available
We present an ice-penetrating radar data set acquired over the Greenland ice sheet by aircraft during the years 1971, 1972, 1974, 1978, and 1979. The data set comprises over 177 000 km of flight lines and contains a wealth of information on the state of the Greenland ice sheet, including information on ice thickness and englacial properties. During...
Article
Full-text available
The firn layer on the Greenland Ice Sheet (GrIS) plays a crucial role in buffering surface meltwater runoff, which is constrained by the available firn pore space and impermeable ice layers that limit deeper meltwater percolation. Understanding these firn properties is essential for predicting current and future meltwater runoff and its contributio...
Preprint
Full-text available
The interaction between glacier fronts and ocean waters is one of the key uncertainties for projecting future ice mass loss. Direct observations at glacier fronts are sparse but studies indicate that the magnitude and timing of freshwater fluxes are crucial in determining fjord circulation, ice frontal melt and ecosystem habitability. Particularly...
Article
Full-text available
Interactions between coastal waters and marine-terminating glaciers in the Polar Regions play a significant role in global sea level rise fueled by a rapidly warming Arctic. The risk of glacier calving, and the abundance of ice, can make it impossible for surface vessels to access the waters near glacier termini. Alternative methods using manned ai...
Article
Full-text available
Sediment discharged from the Greenland Ice Sheet delivers nutrients to marine ecosystems around Greenland and shapes seafloor habitats. Current estimates of the total sediment flux are constrained by observations from land-terminating glaciers only. Addressing this gap, our study presents a budget derived from observations at 30 marine-margin locat...
Preprint
Full-text available
We present an ice-penetrating radar data set acquired over the Greenland ice sheet by aircraft during the years 1971, 1972, 1974, 1978, and 1979. The data set comprises over 177,000 km of flight lines and contains a wealth of information on the state of the Greenland ice sheet including information on ice thickness and englacial properties. During...
Article
Full-text available
Subglacial lakes form beneath ice sheets and ice caps if water is available and if bedrock and surface topography are able to retain the water. On a regional scale, the lakes modulate the timing and rate of freshwater flow through the subglacial system to the ocean by acting as reservoirs. More than 100 hydrologically active subglacial lakes that d...
Data
The SUMup database is a compilation of surface mass balance (SMB), subsurface temperature and density measurements from the Greenland and Antarctic ice sheets available at https://www.doi.org/10.18739/A2M61BR5M (Vandecrux et al., 2023). This 2023 release contains 4 490 442 data points: 1 778 540 SMB measurements, 2 706 413 density measurements and...
Article
Full-text available
The Greenland Climate Network (GC-Net) consists of 31 automatic weather stations (AWSs) at 30 sites across the Greenland Ice Sheet. The first site was initiated in 1990, and the project has operated almost continuously since 1995 under the leadership of the late Konrad Steffen. The GC-Net AWS measured air temperature, relative humidity, wind speed,...
Preprint
Full-text available
The firn layer on the Greenland Ice Sheet (GrIS) plays a crucial role in buffering surface meltwater runoff, which is constrained by the available firn pore space and impermeable ice layers that limit deeper meltwater percolation. Understanding these firn properties is essential for predicting current and future meltwater runoff and its contributio...
Article
Full-text available
Here, we present a compilation of 95 ice temperature profiles from 85 boreholes from the Greenland ice sheet and peripheral ice caps, as well as local ice caps in the Canadian Arctic. Profiles from only 31 boreholes (36 %) were previously available in open-access data repositories. The remaining 54 borehole profiles (64 %) are being made digitally...
Article
Full-text available
The loss of mass from the Greenland ice sheet causes an increasing influx of freshwater to the Greenlandic fjords and the oceans. Freshwater fluxes from marine-terminating glaciers are important to understand fjord circulation and ecosystem dynamics. Here, we present a data set constructed by reformulating existing products into a shared temporal a...
Article
Full-text available
We introduce the design and performance of an electrothermal ice-drilling system designed to insert a temperature sensor cable into ice. The melt tip is relatively simple and low-cost, designed for a one-way trip to the ice–bed interface. The drilling system consists of a melt tip, umbilical cable, winch, interface, power supply, and support items....
Preprint
Full-text available
The Greenland Climate Network (GC-Net) consists of 31 automatic weather stations (AWS) at 30 sites across the Greenland ice sheet. The first site was initiated in 1990, and the project has operated almost continuously since 1995 under 30 the leadership of the late Prof. Konrad Steffen. The GC-Net AWS measured air temperature, relative humidity, win...
Article
Full-text available
Plain Language Summary Above the equilibrium line elevation, seasonal snow is not entirely removed by summer melting. As a result, firn—an interannual layer made of old snow and refrozen meltwater—builds up. Firn holds the potential to buffer sea level rise by trapping liquid water within its pore space. However, surface melting has increased in re...
Preprint
We use airborne accumulation radar data acquired over the Greenland Ice Sheet between 2002 and 2018 to identify changes in ice slab extent and thickness. We show that ice slabs several metres thick were already present at least as early as 2002. Between 2012 and 2018, they expanded 13,400-17,600 inland, or by 37-44%. Our results document that the e...
Technical Report
Geofagene har med deres fokus på samspillet mellem menneske, natur, samfund og miljø unikke muligheder for at bidrage med forskningsmæssige perspektiver på og løsninger til de globale, regionale og lokale udfordringer, som verden står overfor i dag, såsom klimaforandringer, miljøforurening og stigende ulighed. Derfor er det af yderste vigtighed, at...
Article
Full-text available
The dynamics of the Greenland Ice Sheet are affected by surface meltwater reaching the base of the ice, altering ice contact with the bedrock. Lack of understanding of this evolution hampers the ability to predict the effects of increasing temperatures on the Greenland Ice Sheet mass balance. Here we present a unique high-resolution study of ice ve...
Preprint
Full-text available
Subglacial lakes form beneath ice sheets and ice caps if water is available, and if bedrock and surface topography are able to retain the water. On a regional scale, the lakes modulate the timing and rate of freshwater flow through the subglacial system to the ocean by acting as reservoirs. More than one hundred hydrologically active subglacial lak...
Preprint
Full-text available
We use airborne accumulation radar data acquired over the Greenland Ice Sheet between 2002 and 2018 to identify changes in ice slab extent and thickness. We show that ice slabs several metres thick were already present at least as early as 2002. Between 2012 and 2018, they expanded 13,400-17,600 inland, or by 37-44%. Our results document that the e...
Article
Full-text available
The magnitude and azimuth of horizontal ice flow at Camp Century, Greenland have been measured several times since 1963. Here, we provide a further two independent measurements over the 2017–21 period. Our consensus estimate of horizontal ice flow from four independent satellite-positioning solutions is 3.65 ± 0.13 m a ⁻¹ at an azimuth of 236 ± 2°....
Preprint
Full-text available
We introduce the design and performance of a melt-tip ice-drilling system designed to insert a temperature sensor cable into ice. The melt tip is relatively simple and low cost, designed for a one-way trip to the ice-bed interface. The drilling system consists of a melt tip, umbilical cable, winch, interface, power supply, and support items. The me...
Article
Full-text available
Mass loss near the ice-sheet margin is evident from remote sensing as frontal retreat and increases in ice velocities. Velocities in the ice sheet interior are orders of magnitude smaller, making it challenging to detect velocity change. Here, we analyze a 35-year record of remotely sensed velocities, and a 6-year record of repeated GPS observation...
Preprint
Full-text available
Here, we present a compilation of 85 ice temperature profiles from 79 boreholes from the Greenland Ice Sheet and peripheral ice caps, as well as local ice caps in the Canadian Arctic. Only 25 profiles (32 %) were previously available in open-access data repositories. The remaining 54 profiles (68 %) are being made digitally available here for the f...
Article
Full-text available
The basal thermal state (frozen or thawed) of the Greenland Ice Sheet is under-constrained due to few direct measurements, yet knowledge of this state is becoming increasingly important to interpret modern changes in ice flow. The first synthesis of this state relied on inferences from widespread airborne and satellite observations and numerical mo...
Article
Full-text available
We compile and analyze all available geothermal heat flow measurements collected in and around Greenland into a new database of 419 sites and generate an accompanying spatial map. This database includes 290 sites previously reported by the International Heat Flow Commission (IHFC), for which we now standardize measurement and metadata quality. This...
Preprint
Full-text available
The basal thermal state (frozen or thawed) of the Greenland Ice Sheet is under-constrained due to few direct measurements, yet knowledge of this state is becoming increasingly important to interpret modern changes in ice flow. The first synthesis of this state relied on inferences from widespread airborne and satellite observations and numerical mo...
Article
Full-text available
We propose the exploration of polar areas on Mars by a next-generation orbiter mission. In particular, we aim at studying the seasonal and regional variations in snow-deposits, which – in combination with measurements of temporal variations in rotation and gravity field – will improve models of the global planetary CO2 cycle. A monitoring of polar...
Conference Paper
Subglacial lakes may form beneath ice sheets and ice caps, given the availability of water and appropriate bedrock and surface topography to capture the water. On a regional scale, these lakes can modulate the freshwater output to the ocean by acting as reservoirs that may periodically drain and recharge. Several such active subglacial lakes have b...
Article
Full-text available
Basal conditions play an essential role in the dynamics of outlet glaciers, but direct observations at the bed of glaciers are challenging to obtain. Instead, inverse methods can be used to infer basal parameters from surface observations. Here, we use a simple ice-flow model as a forward model in an inversion scheme to retrieve the spatio-temporal...
Article
Full-text available
The mass of the Greenland ice sheet is declining as mass gain from snow accumulation is exceeded by mass loss from surface meltwater runoff, marine-terminating glacier calving and submarine melting, and basal melting. Here we use the input–output (IO) method to estimate mass change from 1840 through next week. Surface mass balance (SMB) gains and l...
Preprint
Full-text available
We compile, analyse and map all available geothermal heat flow measurements collected in and around Greenland into a new database of 419 sites and generate an accompanying spatial map. This database includes 290 sites previously reported by the International Heat Flow Commission (IHFC), for which we now standardize measurement and metadata quality....
Article
Full-text available
The Programme for Monitoring of the Greenland Ice Sheet (PROMICE) has been measuring climate and ice sheet properties since 2007. Currently, the PROMICE automatic weather station network includes 25 instrumented sites in Greenland. Accurate measurements of the surface and near-surface atmospheric conditions in a changing climate are important for r...
Article
Full-text available
We present the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) Ice Velocity product (10.22008/promice/data/sentinel1icevelocity/greenlandicesheet, ), which is a time series of Greenland Ice Sheet ice velocity mosaics spanning September 2016 through to the present. The product is based on Sentinel-1 synthetic aperture radar data and ha...
Article
Full-text available
The Greenland ice sheet has been one of the largest sources of sea-level rise since the early 2000s. However, basal melt has not been included explicitly in assessments of ice-sheet mass loss so far. Here, we present the first estimate of the total and regional basal melt produced by the ice sheet and the recent change in basal melt through time. W...
Article
Full-text available
Understanding the contribution of the West Antarctic Ice Sheet (WAIS) to past and future sea level has been a major scientific priority over the last three decades. In recent years, observed thinning and ice‐flow acceleration of the marine‐based Pine Island Glacier has highlighted that understanding dynamic changes is critical to predicting the lon...
Preprint
Full-text available
The mass of the Greenland ice sheet is declining as mass gain from snowfall is exceeded by mass loss from surface meltwater runoff, marine-terminating glacier calving and submarine melting, and basal melting. Here we use the input/output (IO) method to estimate mass change from 1840 through next week. Mass gains come from three regional climate mod...
Article
Full-text available
Camp Century is an American military base built in 1959 under the surface of the Greenland ice sheet and decommissioned in 1967. Here, we use outputs from RACMO2.3p2 and CanESM2 climate models, adjusted to meteorological observations, and a firn model to simulate the firn density and temperature at Camp Century between 1966 and 2100. The model outp...
Preprint
Full-text available
The Programme for Monitoring of the Greenland Ice Sheet (PROMICE) has been measuring climate and ice sheetproperties since 2007. Currently the PROMICE automatic weather station network includes 25 instrumented sites in Greenland.Accurate measurements of the surface and near-surface atmospheric conditions in a changing climate is important for relia...
Article
Full-text available
Subglacial hydrological systems require innovative technological solutions to access and observe. Wireless sensor platforms can be used to collect and return data, but their performance in deep and fast-moving ice requires quantification. We report experimental results from Cryoegg: a spherical probe that can be deployed into a borehole or moulin a...
Preprint
Full-text available
We present the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) ice velocity product (https://doi.org/10.22008/promice/data/sentinel1icevelocity/greenlandicesheet) (Solgaard and Kusk, 2021)) which is a September 2016 through present time series of Greenland Ice Sheet ice-velocity mosaics. The product is based on Sentinel-1 synthetic ap...
Data
This dataset contains the position and depth of four spatially extensive Internal Reflecting Horizons (or IRHs) traced on the British Antarctic Survey's PASIN system and NASA Operation IceBridge's MCoRDS2 system across the Pine Island Glacier catchment. Using the WAIS Divide icecore chronology and a 1D steadystate model, we assign ages to our four...
Preprint
Full-text available
In a warming climate concise knowledge of the mass balance of the Greenland ice sheet is of utter importance. Speculations that current warming will increase the snow accumulation and mitigate mass balance losses are unconstrained as accumulation data across large regions of the northern ice sheet are scarce. We reconstructed the accumulation from...
Article
Full-text available
This paper provides the first chronology for the deep ice core from the East Greenland Ice-core Project (EGRIP) over the Holocene and the late last glacial period. We rely mainly on volcanic events and common peak patterns recorded by dielectric profiling (DEP) and electrical conductivity measurement (ECM) for the synchronization between the EGRIP,...
Article
Full-text available
The Northeast Greenland Ice Stream (NEGIS) extends around 600 km upstream from the coast to its onset near the ice divide in interior Greenland. Several maps of surface velocity and topography of interior Greenland exist, but their accuracy is not well constrained by in situ observations. Here we present the results from a GPS mapping of surface ve...
Preprint
Full-text available
The Greenland ice sheet is one of the largest sources of sea-level rise since the early 2000s. Basal melt has not been included explicitly in assessments of ice-sheet mass loss so far. Here, we present the first full-coverage estimate of the ice-sheet wide basal melt in Greenland and its recent change through time. We find that presently basal melt...
Preprint
Full-text available
Subglacial hydrological systems require innovative technological solutions to access and observe. Wireless sensor platforms can be used to collect and return data, but their performance in deep and fast-moving ice requires quantification. We report experimental results from Cryoegg: a spherical probe that can be deployed into a borehole or moulin a...
Article
Full-text available
The internal stratigraphy of snow and ice as imaged by ground-penetrating radar may serve as a source of information on past accumulation. This study presents results from two ground-based radar surveys conducted in Greenland in 2007 and 2015, respectively. The first survey was conducted during the traverse from the ice-core station NGRIP (North Gr...
Preprint
Full-text available
Abstract. The Northeast Greenland Ice Stream (NEGIS) extends around 600 km upstream from the coast to its onset near the ice divide in interior Greenland. Several maps of surface velocity and topography in the interior Greenland exist, but the accuracy is not well constrained by in situ observations and limiting detailed studies of flow structures...
Presentation
Full-text available
Cryoegg: development and field trials of a wireless subglacial probe for deep, fast-moving ice
Article
Full-text available
On 30 September 2017, an Air France Airbus A380-800 suffered a failure of its fourth engine while over Greenland. This failure resulted in the loss of the engine fan hub, fan blades and surrounding structure. An initial search recovered 30 pieces of light debris, but the primary part of interest, a ~220 kg titanium fan hub, was not recovered becaus...
Article
Full-text available
We use remotely sensed ice velocities in combination with observations of surface elevation and glacier area change to investigate the dynamics of Hagen Bræ, North Greenland in high detail over the last 35 years. From our data, we can establish for the first time that Hagen Bræ is a surge-type glacier with characteristics of both Alaskan- and Svalb...
Article
Full-text available
Radar sounding is a powerful geophysical approach for characterizing the subsurface conditions of terrestrial and planetary ice masses at local to global scales. As a result, a wide array of orbital, airborne, ground-based, and in situ instruments, platforms and data analysis approaches for radioglaciology have been developed, applied or proposed....
Article
Full-text available
The Antarctic ice sheet has been losing mass over past decades through the accelerated flow of its glaciers, conditioned by ocean temperature and bed topography. Glaciers retreating along retrograde slopes (that is, the bed elevation drops in the inland direction) are potentially unstable, while subglacial ridges slow down the glacial retreat. Desp...
Preprint
Full-text available
Abstract. This paper provides the first chronology for the deep ice core from the East GReenland Ice-core Project (EGRIP) over the Holocene and late last glacial period. We rely mainly on volcanic events and common patterns of peaks in dielectric profiling (DEP), electrical conductivity measurements (ECM) and tephra records for the synchronization...