scholarly journals Greenland Ice Mapping Project: Ice Flow Velocity Variation at submonthly to decadal time scales

2018 ◽  
Author(s):  
Ian Joughin ◽  
Ben E. Smith ◽  
Ian Howat
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Velocity Variation ◽  
Landsat 8 ◽  
Ice Flow ◽  
Speed Up ◽  
Ice Velocity ◽  
Year 2000 ◽  
The Impact ◽  
Ice Sheet Mapping

Abstract. We describe several new ice velocity maps produced by the Greenland Ice Sheet Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel 1A/B data. We then focus on several sites where we analyse these data in conjunction with earlier data from this project, which extend back to the year 2000. At Jakobshavn Isbrae and Koge Bugt, we find good agreement when comparing results from different sensors. In a change from recent behaviour, Jakobshavn Isbrae began slowing substantially in 2017, with a mid-summer peak that was even slower than some previous winter minimums. Over the last decade, we identify two major slowdown events at Koge Bugt that coincide with short-term advances of the terminus. We also examined populations of glaciers in northwest and southwest Greenland to produce a record of speedup since 2000. Collectively these glaciers continue to speed up, but there are regional differences in the timing of periods of peak speedup. In addition, we computed trends for much of the southwest margin of the ice sheet where other work has suggested slowing ice flow in response to increased melting. Contrary to the earlier results, we find no evidence for a slowdown distributed over a wide area. Finally, although consistency of the data generally is good through time and across sensors, our analysis indicates substantial differences can arise in regions with high strain rates (e.g., shear margins) where sensor resolution can become a factor. For applications such as constraining model inversions, users should factor in the impact that the data's resolution has on their results.

scholarly journals Greenland Ice Mapping Project: ice flow velocity variation at sub-monthly to decadal timescales

2018 ◽  
Vol 12 (7) ◽  
pp. 2211-2227 ◽  
Author(s):  
Ian Joughin ◽  
Ben E. Smith ◽  
Ian Howat
Keyword(s):  
Flow Speed ◽  
Velocity Variation ◽  
Landsat 8 ◽  
North West ◽  
South West ◽  
Speed Up ◽  
Ice Velocity ◽  
Year 2000 ◽  
The Impact ◽  
Good Agreement

Abstract. We describe several new ice velocity maps produced by the Greenland Ice Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel 1A/B data. We then focus on several sites where we analyse these data in conjunction with earlier data from this project, which extend back to the year 2000. At Jakobshavn Isbræ and Køge Bugt, we find good agreement when comparing results from different sensors. In a change from recent behaviour, Jakobshavn Isbræ began slowing substantially in 2017, with a midsummer peak that was even slower than some previous winter minima. Over the last decade, we identify two major slowdown events at Køge Bugt that coincide with short-term advances of the terminus. We also examined populations of glaciers in north-west and south-west Greenland to produce a record of speed-up since 2000. Collectively these glaciers continue to speed up, but there are regional differences in the timing of periods of peak speed-up. In addition, we computed trends in winter flow speed for much of the south-west margin of the ice sheet and find little in the way of statistically significant changes over the period covered by our data. Finally, although the consistency of the data is generally good over time and across sensors, our analysis indicates that substantial differences can arise in regions with high strain rates (e.g. shear margins) where sensor resolution can become a factor. For applications such as constraining model inversions, users should factor in the impact that the data's resolution has on their results.

5 Years of Polar Land Ice Velocity and Discharge observed by Sentinel-1

2020 ◽  
Author(s):  
Jan Wuite ◽  
Thomas Nagler ◽  
Markus Hetzenecker ◽  
Lars Keuris ◽  
Ludivine Libert ◽  
...  
Keyword(s):  
Climate Change ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Polar Regions ◽  
Space Applications ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Temporal Sampling ◽  
Acquisition Scheme ◽  
Ice Velocity

<p>Recent years have seen major advancements in satellite Earth observation of polar land ice. Among the most notable are the developments enabled by the Copernicus Sentinel program, including the Sentinel-1 SAR mission. The Sentinel-1 constellation, with its dedicated polar acquisition scheme, has provided the opportunity to derive ice flow velocity of the Greenland and Antarctic ice sheets at an unprecedented scale and temporal sampling. A continuous observational record of the ice sheet margins since October 2014, augmented by dedicated ice sheet wide mapping campaigns, enabled the operational monitoring of key climate variables like ice velocity and glacier discharge. In 2019 additional tracks have been added to the regular acquisition scheme, covering the slow-moving interior of the Greenland Ice Sheet, opening up new opportunities for interferometric applications and permitting to derive monthly ice sheet wide velocity maps. </p><p><br>Based on repeat pass Sentinel-1 SAR data, acquired in Interferometric Wide (IW) swath mode, we have generated a dense archive of ice velocity maps covering the polar regions and encompassing the entire mission duration, now spanning well over 5 years. Including the latest observational data, we present ice velocity maps of Greenland, Antarctica and other major ice caps, focusing on time series of ice flow fluctuations of major outlet glaciers. The ice velocity maps, complemented by high resolution DEMs and ice thickness data, form the basis for studying ice dynamics and discharge fluctuations and trends at sub-monthly to multi-annual time scales. Our results underscore the value of long-term comprehensive monitoring of the polar ice masses, which is vital for to gain insight for predicting their response to ongoing climate warming.</p><p>This poster highlights some of the main achievements and latest developments of 5 years of Sentinel-1 ice flow mapping in the Polar regions facilitated by the ESA Climate Change Initiative (CCI), EU Copernicus Climate Change Service (C3S) and Austrian Space Applications Programme (ASAP). </p>

scholarly journals A complete map of Greenland ice velocity derived from satellite data collected over 20 years

2017 ◽  
Vol 64 (243) ◽  
pp. 1-11 ◽  
Author(s):  
IAN JOUGHIN ◽  
BEN E. SMITH ◽  
IAN M. HOWAT
Keyword(s):  
Flow Velocity ◽  
Feature Tracking ◽  
Ice Sheet ◽  
Synthetic Aperture ◽  
Landsat 8 ◽  
Ice Flow ◽  
Interferometric Phase ◽  
Ice Velocity ◽  
Slow Moving ◽  
Good Agreement

ABSTRACTWhile numerous maps of Greenland ice flow velocity exist, most have gaps in coverage and/or accuracy is limited. We processed a large volume of synthetic aperture radar and Landsat 8 imagery collected between 1995 and 2015 to produce a nearly complete map of ice flow velocity for Greenland at a far greater accuracy than most prior products. We evaluated the accuracy of this map by comparing it with a variety of measured and estimated velocities. For the slow-moving interior of the ice sheet, where estimates are determined from interferometric phase, the errors are ~2 m a−1 or better. For coastal areas, where estimates are determined entirely from speckle- or feature-tracking methods, errors are 2–3 m a−1, which is in good agreement with the estimated formal errors. Especially for the slow-moving majority of the ice sheet, this map provides an important source of data for numerous types of glaciological studies.

scholarly journals The annual glaciohydrology cycle in the ablation zone of the Greenland ice sheet: Part 1. Hydrology model

2011 ◽  
Vol 57 (204) ◽  
pp. 697-709 ◽  
Author(s):  
William Colgan ◽  
Harihar Rajaram ◽  
Robert Anderson ◽  
Konrad Steffen ◽  
Thomas Phillips ◽  
...  
Keyword(s):  
Residence Time ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Hydraulic Head ◽  
Ablation Zone ◽  
Hydrology Model ◽  
Hydrologic System ◽  
Speed Up ◽  
Ice Velocity ◽  
Subglacial Drainage

AbstractWe apply a novel one-dimensional glacier hydrology model that calculates hydraulic head to the tidewater-terminating Sermeq Avannarleq flowline of the Greenland ice sheet. Within a plausible parameter space, the model achieves a quasi-steady-state annual cycle in which hydraulic head oscillates close to flotation throughout the ablation zone. Flotation is briefly achieved during the summer melt season along a ∼17 km stretch of the ∼50 km of flowline within the ablation zone. Beneath the majority of the flowline, subglacial conduit storage ‘closes’ (i.e. obtains minimum radius) during the winter and ‘opens’ (i.e. obtains maximum radius) during the summer. Along certain stretches of the flowline, the model predicts that subglacial conduit storage remains open throughout the year. A calculated mean glacier water residence time of ∼2.2 years implies that significant amounts of water are stored in the glacier throughout the year. We interpret this residence time as being indicative of the timescale over which the glacier hydrologic system is capable of adjusting to external surface meltwater forcings. Based on in situ ice velocity observations, we suggest that the summer speed-up event generally corresponds to conditions of increasing hydraulic head during inefficient subglacial drainage. Conversely, the slowdown during fall generally corresponds to conditions of decreasing hydraulic head during efficient subglacial drainage.

scholarly journals Data Reduction Using Statistical and Regression Approaches for Ice Velocity Derived by Landsat-8, Sentinel-1 and Sentinel-2

2020 ◽  
Vol 12 (12) ◽  
pp. 1935
Author(s):  
Anna Derkacheva ◽  
Jeremie Mouginot ◽  
Romain Millan ◽  
Nathan Maier ◽  
Fabien Gillet-Chaulet
Keyword(s):  
Time Series ◽  
Greenland Ice Sheet ◽  
Landsat 8 ◽  
Post Processing ◽  
Local Regression ◽  
Ice Flow ◽  
Ice Velocity ◽  
Noisy Measurements ◽  
Different Characteristics ◽  
Sentinel 2

During the last decade, the number of available satellite observations has increased significantly, allowing for far more frequent measurements of the glacier speed. Appropriate methods of post-processing need to be developed to efficiently deal with the large volumes of data generated and relatively large intrinsic errors associated with the measurements. Here, we process and combine together measurements of ice velocity of Russell Gletscher in Greenland from three satellites—Sentinel-1, Sentinel-2, and Landsat-8, creating a multi-year velocity database with high temporal and spatial resolution. We then investigate post-processing methodologies with the aim of generating corrected, ordered, and simplified time series. We tested rolling mean and median, cubic spline regression, and linear non-parametric local regression (LOWESS) smoothing algorithms to reduce data noise, evaluated the results against ground-based GPS in one location, and compared the results between two locations with different characteristics. We found that LOWESS provides the best solution for noisy measurements that are unevenly distributed in time. Using this methodology with these sensors, we can robustly derive time series with temporal resolution of 2–3 weeks and improve the accuracy on the ice velocity to about 10 m/yr, or a factor of three compared to the initial measurements. The presented methodology could be applied to the entire Greenland ice sheet with an aim of reconstructing comprehensive sub-seasonal ice flow dynamics and mass balance.

scholarly journals Consequences of the 2019 Greenland Ice Sheet Melt Episode on Albedo

2021 ◽  
Vol 13 (2) ◽  
pp. 227
Author(s):  
Arthur Elmes ◽  
Charlotte Levy ◽  
Angela Erb ◽  
Dorothy K. Hall ◽  
Ted A. Scambos ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Surface Albedo ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Energy Budget ◽  
Landsat 8 ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Seasonal Snow Cover

In mid-June 2019, the Greenland ice sheet (GrIS) experienced an extreme early-season melt event. This, coupled with an earlier-than-average melt onset and low prior winter snowfall over western Greenland, led to a rapid decrease in surface albedo and greater solar energy absorption over the melt season. The 2019 melt season resulted in significantly more melt than other recent years, even compared to exceptional melt years previously identified in the moderate-resolution imaging spectroradiometer (MODIS) record. The increased solar radiation absorbance in 2019 warmed the surface and increased the rate of meltwater production. We use two decades of satellite-derived albedo from the MODIS MCD43 record to show a significant and extended decrease in albedo in Greenland during 2019. This decrease, early in the melt season and continuing during peak summer insolation, caused increased radiative forcing of the ice sheet of 2.33 Wm−2 for 2019. Radiative forcing is strongly influenced by the dramatic seasonal differences in surface albedo experienced by any location experiencing persistent and seasonal snow-cover. We also illustrate the utility of the newly developed Landsat-8 albedo product for better capturing the detailed spatial heterogeneity of the landscape, leading to a more refined representation of the surface energy budget. While the MCD43 data accurately capture the albedo for a given 500 m pixel, the higher spatial resolution 30 m Landsat-8 albedos more fully represent the detailed landscape variations.

Greenland land-terminating glaciers velocity trends during the last two decades

2021 ◽  
Author(s):  
Paul Halas ◽  
Jeremie Mouginot ◽  
Basile de Fleurian ◽  
Petra Langebroek
Keyword(s):  
Water Pressure ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Melting ◽  
Limited Area ◽  
Ice Dynamics ◽  
Basal Sliding ◽  
Surface Melt ◽  
Ice Sheet Dynamics ◽  
The Impact

<div> <p>Ice losses from the Greenland Ice Sheet have been increasing in the last two decades, leading to a larger contribution to the global sea level rise. Roughly 40% of the contribution comes from ice-sheet dynamics, mainly regulated by basal sliding. The sliding component of glaciers has been observed to be strongly related to surface melting, as water can eventually reach the bed and impact the subglacial water pressure, affecting the basal sliding.  </p> </div><div> <p>The link between ice velocities and surface melt on multi-annual time scale is still not totally understood even though it is of major importance with expected increasing surface melting. Several studies showed some correlation between an increase in surface melt and a slowdown in velocities, but there is no consensus on those trends. Moreover those investigations only presented results in a limited area over Southwest Greenland.  </p> </div><div> <p>Here we present the ice motion over many land-terminating glaciers on the Greenland Ice Sheet for the period 2000 - 2020. This type of glacier is ideal for studying processes at the interface between the bed and the ice since they are exempted from interactions with the sea while still being relevant for all glaciers since they share the same basal friction laws. The velocity data was obtained using optical Landsat 7 & 8 imagery and feature-tracking algorithm. We attached importance keeping the starting date of our image pairs similar, and avoided stacking pairs starting before and after melt seasons, resulting in multiple velocity products for each year.  </p> </div><div> <p>Our results show similar velocity trends for previously studied areas with a slowdown until 2012 followed by an acceleration. This trend however does not seem to be observed on the whole ice sheet and is probably specific to this region’s climate forcing. </p> </div><div> <p>Moreover comparison between ice velocities from different parts of Greenland allows us to observe the impact of different climatic trends on ice dynamics.</p> </div>

Early Holocene ocean conditions off the Zachariæ Isstrøm, Northeast Greenland

2021 ◽  
Author(s):  
Joanna Davies ◽  
Anders Møller Mathiasen ◽  
Kristiane Kristensen ◽  
Christof Pearce ◽  
Marit-Solveig Seidenkrantz
Keyword(s):  
Climate Change ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Atlantic Water ◽  
The Arctic ◽  
Future Climate Change ◽  
Polar Regions ◽  
Ice Shelf ◽  
Outlet Glacier ◽  
The Impact

<p>The polar regions exhibit some of the most visible signs of climate change globally; annual mass loss from the Greenland Ice Sheet (GrIS) has quadrupled in recent decades, from 51 ± 65 Gt yr<sup>−1</sup> (1992-2001) to 211 ± 37 Gt yr<sup>−1</sup> (2002-2011). This can partly be attributed to the widespread retreat and speed-up of marine-terminating glaciers. The Zachariae Isstrøm (ZI) is an outlet glacier of the Northeast Greenland Ice Steam (NEGIS), one of the largest ice streams of the GrIS (700km), draining approximately 12% of the ice sheet interior. Observations show that the ZI began accelerating in 2000, resulting in the collapse of the floating ice shelf between 2002 and 2003. By 2014, the ice shelf extended over an area of 52km<sup>2</sup>, a 95% decrease in area since 2002, where it extended over 1040km<sup>2</sup>. Paleo-reconstructions provide an opportunity to extend observational records in order to understand the oceanic and climatic processes governing the position of the grounding zone of marine terminating glaciers and the extent of floating ice shelves. Such datasets are thus necessary if we are to constrain the impact of future climate change projections on the Arctic cryosphere.</p><p>A multi-proxy approach, involving grain size, geochemical, foraminiferal and sedimentary analysis was applied to marine sediment core DA17-NG-ST8-92G, collected offshore of the ZI, on  the Northeast Greenland Shelf. The aim was to reconstruct changes in the extent of the ZI and the palaeoceanographic conditions throughout the Early to Mid Holocene (c.a. 12,500-5,000 cal. yrs. BP). Evidence from the analysis of these datasets indicates that whilst there has been no grounded ice at the site over the last 12,500 years, the ice shelf of the ZI extended as a floating ice shelf over the site between 12,500 and 9,200 cal. yrs. BP, with the grounding line further inland from our study site. This was followed by a retreat in the ice shelf extent during the Holocene Thermal Maximum; this was likely to have been governed, in part, by basal melting driven by Atlantic Water (AW) recirculated from Svalbard or from the Arctic Ocean. Evidence from benthic foraminifera suggest that there was a shift from the dominance of AW to Polar Water at around 7,500 cal. yrs. BP, although the ice shelf did not expand again despite of this cooling of subsurface waters.</p>

scholarly journals Last Interglacial climate and sea-level evolution from a coupled ice sheet–climate model

2016 ◽  
Vol 12 (12) ◽  
pp. 2195-2213 ◽  
Author(s):  
Heiko Goelzer ◽  
Philippe Huybrechts ◽  
Marie-France Loutre ◽  
Thierry Fichefet
Keyword(s):  
Surface Temperature ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Last Interglacial ◽  
A Minor ◽  
The Antarctic ◽  
The Impact ◽  
And Sea Level

Abstract. As the most recent warm period in Earth's history with a sea-level stand higher than present, the Last Interglacial (LIG,  ∼  130 to 115 kyr BP) is often considered a prime example to study the impact of a warmer climate on the two polar ice sheets remaining today. Here we simulate the Last Interglacial climate, ice sheet, and sea-level evolution with the Earth system model of intermediate complexity LOVECLIM v.1.3, which includes dynamic and fully coupled components representing the atmosphere, the ocean and sea ice, the terrestrial biosphere, and the Greenland and Antarctic ice sheets. In this setup, sea-level evolution and climate–ice sheet interactions are modelled in a consistent framework.Surface mass balance change governed by changes in surface meltwater runoff is the dominant forcing for the Greenland ice sheet, which shows a peak sea-level contribution of 1.4 m at 123 kyr BP in the reference experiment. Our results indicate that ice sheet–climate feedbacks play an important role to amplify climate and sea-level changes in the Northern Hemisphere. The sensitivity of the Greenland ice sheet to surface temperature changes considerably increases when interactive albedo changes are considered. Southern Hemisphere polar and sub-polar ocean warming is limited throughout the Last Interglacial, and surface and sub-shelf melting exerts only a minor control on the Antarctic sea-level contribution with a peak of 4.4 m at 125 kyr BP. Retreat of the Antarctic ice sheet at the onset of the LIG is mainly forced by rising sea level and to a lesser extent by reduced ice shelf viscosity as the surface temperature increases. Global sea level shows a peak of 5.3 m at 124.5 kyr BP, which includes a minor contribution of 0.35 m from oceanic thermal expansion. Neither the individual contributions nor the total modelled sea-level stand show fast multi-millennial timescale variations as indicated by some reconstructions.

scholarly journals The Holocene thermal maximum in the Nordic Seas: the impact of Greenland Ice Sheet melt and other forcings in a coupled atmosphere–sea-ice–ocean model

2013 ◽  
Vol 9 (4) ◽  
pp. 1629-1643 ◽  
Author(s):  
M. Blaschek ◽  
H. Renssen
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Early Holocene ◽  
Surface Cooling ◽  
Holocene Climate ◽  
Nordic Seas ◽  
The Holocene ◽  
Holocene Thermal Maximum ◽  
Thermal Maximum ◽  
The Impact

Abstract. The relatively warm early Holocene climate in the Nordic Seas, known as the Holocene thermal maximum (HTM), is often associated with an orbitally forced summer insolation maximum at 10 ka BP. The spatial and temporal response recorded in proxy data in the North Atlantic and the Nordic Seas reveals a complex interaction of mechanisms active in the HTM. Previous studies have investigated the impact of the Laurentide Ice Sheet (LIS), as a remnant from the previous glacial period, altering climate conditions with a continuous supply of melt water to the Labrador Sea and adjacent seas and with a downwind cooling effect from the remnant LIS. In our present work we extend this approach by investigating the impact of the Greenland Ice Sheet (GIS) on the early Holocene climate and the HTM. Reconstructions suggest melt rates of 13 mSv for 9 ka BP, which result in our model in an ocean surface cooling of up to 2 K near Greenland. Reconstructed summer SST gradients agree best with our simulation including GIS melt, confirming that the impact of the early Holocene GIS is crucial for understanding the HTM characteristics in the Nordic Seas area. This implies that modern and near-future GIS melt can be expected to play an active role in the climate system in the centuries to come.

Sign in / Sign up

Export Citation Format

Share Document