Monitoring the Petermann Ice Island with TanDEM-X

This paper presents the processing of TanDEM-X acquisitions for the monitoring of the topography of the Petermann ice island. In this particular case the area under study is continuously moving and the acquisition geometry is changing, so the processing of the iceberg’s DEMs is challenging and additional effects are to be considered. The SAR processing chain used is presented and the results obtained summarized, showing the effects and limitations observed during the process

Grounding line migration from 1992 to 2011 on Petermann Glacier, North-West Greenland

We use satellite radar interferometry to investigate changes in the location of the Petermann Glacier grounding line between 1992 and 2011. The grounding line location was identified in 17 quadruple-difference interferograms produced from European Remote Sensing (ERS)-1/2 data – the most extensive time series assembled at any ice stream to date. There is close agreement (20.6 cm) between vertical displacement of the floating ice shelf and relative tide amplitudes simulated by the Arctic Ocean Dynamics-based Tide Model 5 (AODTM-5) Arctic tide model. Over the 19 a period, the groundling line position varied by 470 m, on average, with a maximum range of 7.0 km observed on the north-east margin of the ice stream. Although the mean range (2.8 km) and variability (320 m) of the grounding line position is considerably lower if the unusually variable north-east sector is not considered, our observations demonstrate that large, isolated movements cannot be precluded, thus sparse temporal records should be analysed with care. The grounding line migration observed on Petermann Glacier is not significantly correlated with time (R2 = 0.22) despite reported ice shelf thinning and episodes of large iceberg calving, which suggests that unlike other ice streams, on the south-west margin of the Greenland ice sheet, Petermann Glacier is dynamically stable

Iceberg topography and volume classification using TanDEM-X interferometry

Icebergs in polar regions affect water salinity, alter marine habitats, and impose serious hazards on maritime operations and navigation. These impacts mainly depend on the iceberg volume, which remains an elusive parameter to measure. We investigate the capability of TanDEM-X bistatic single-pass synthetic aperture radar interferometry (InSAR) to derive iceberg subaerial morphology and infer total volume. We cross-verify InSAR results with Operation IceBridge (OIB) data acquired near Wordie Bay, Antarctica, as part of the OIB/TanDEM-X Antarctic Science Campaign (OTASC). While icebergs are typically classified according to size based on length or maximum height, we develop a new volumetric classification approach for applications where iceberg volume is relevant. For icebergs with heights exceeding 5 m, we find iceberg volumes derived from TanDEM-X and OIB data match within 7 %. We also derive a range of possible iceberg keel depths relevant to grounding and potential impacts on subsea installations. These results suggest that TanDEM-X could pave the way for future single-pass interferometric systems for scientific and operational iceberg mapping and classification based on iceberg volume and keel depth

Locating Ice Sheet Grounding Lines Using Satellite Radar Interferometry and Altimetry

In this thesis, I use synthetic aperture radar (SAR) and radar altimeter data to make new observations of Antarctic and Greenland ice sheet grounding lines. I use ERS SAR data acquired between 1992 and 2011 to map the Petermann Glacier grounding line on 17 occasions using quadruple difference interferometric SAR (QDInSAR). Over the 19-year period, the grounding line position varied by 0.5 km, on average, with no significant trend over time. Although tidal forcing explains a fraction (34 %) of the movement, localised variations in the glacier thickness could explain it all were they to alter the glaciers hydrostatic balance as they advect downstream – a hitherto unconsidered possibility that would reduce the accuracy with which changes in grounding line position can be detected. Next, I developed a new technique for detecting grounding lines using differential range direction offset tracking (DRDOT) in incoherent SAR data. I then applied this technique to a sequence of 11 TerraSAR-X images acquired in 2009 over Petermann Glacier. The DRDOT technique is able to reproduce the shape and location of the grounding line with an estimated lateral precision of 0.8 km and, although this is 30 times poorer than QDInSAR, provides a complementary method given the paucity of coherent SAR data. Finally, I developed another new method for detecting the grounding line as the break in ice sheet surface slope computed from CryoSat-2 elevation measurements. I then applied this technique to map grounding lines in the sectors of Antarctica buttressed by the Filchner-Ronne, Ekström, Larsen-C, and Amundsen Sea ice shelves. The technique is able to map the grounding line to within 4.5 km, on average, and, although this is far poorer than either QDInSAR or DRDOT, it is computationally efficient and can succeed where SAR-based methods fail, offering an additional complementary approach

FABIAN: A daily product of fractional austral-summer blue ice over Antarctica during 2000-2021 based on MODIS imagery using Google Earth Engine

Antarctic blue ice areas are exposed due to erosion and sublimation of snow. At the same time, surface melt can form surface types that are spectrally similar to blue ice, especially at low elevations. These are termed melt-induced blue ice areas. Both types of blue ice are sensitive indicators of climate change. Satellite remote sensing is a powerful technique to retrieve the spatial extent of blue ice areas and their variation in time. Yet, existing satellite-derived blue ice area products are either mono-temporal for the entire Antarctic ice sheet, or multi-temporal for a limited area. Here, we present FABIAN, a product of blue ice fraction over Antarctica, derived from the moderate resolution imaging spectroradiometer (MODIS) archive covering the period 2000–2021. A spectral mixture analysis (SMA) in Google Earth Engine, based on a careful selection of endmember spectra, accurately reconstructs the reflectance observed by MODIS in blue ice areas. Based on a validation with contemporaneous Sentinel-2 images, FABIAN has a root mean square error in blue ice fraction of approximately 10% ∼ 20% in wind-induced blue ice areas, and 20% ∼ 30% in melt-induced blue ice areas across six selected test sites in the coastal East Antarctic ice sheet. FABIAN is challenged in regions with shallow melt streams and lakes, since their spectral profiles are similar to those from blue ice areas in MODIS bands. For further analyses and applications, FABIAN holds the potential for (1) deriving annual blue ice area maps, (2) distinguishing between wind-and melt-induced blue ice types, (3) evaluating and correcting (regional) climate models, and (4) analyzing temporal variations in blue ice abundance and exposure

Program for Arctic Regional Climate Assessment (PARCA)

The Program for Arctic Regional Climate Assessment (PARCA) is a NASA-sponsored initiative with the prime objective of understanding the mass balance of the Greenland ice sheet. In October 1998, PARCA investigators met to review activities of the previous year, assess the program's progress, and plan future investigations directed at accomplishing that objective. Some exciting results were presented and discussed, including evidence of dramatic thinning of the ice sheet near the southeastern coast. Details of the investigations and many of the accomplishments are given in this report, but major highlights are given in the Executive Summary of the report

On the evolution of an ice shelf melt channel at the base of Filchner Ice Shelf, from observations and viscoelastic modeling

Ice shelves play a key role in the stability of the Antarctic Ice Sheet due to their buttressing effect. A loss of buttressing as a result of increased basal melting or ice shelf disintegration will lead to increased ice discharge. Some ice shelves exhibit channels at the base that are not yet fully understood. In this study, we present in situ melt rates of a channel which is up to 330 m high and located in the southern Filchner Ice Shelf. Maximum observed melt rates are 2 m yr−1. Melt rates inside the channel decrease in the direction of ice flow and turn to freezing ∼55 km downstream of the grounding line. While closer to the grounding line melt rates are higher within the channel than outside, this relationship reverses further downstream. Comparing the modeled evolution of this channel under present-day climate conditions over 250 years with its present geometry reveals a mismatch. Melt rates twice as large as the present-day values are required to fit the observed geometry. In contrast, forcing the model with present-day melt rates results in a closure of the channel, which contradicts observations. The ice shelf experiences strong tidal variability in vertical strain rates at the measured site, and discrete pulses of increased melting occurred throughout the measurement period. The type of melt channel in this study diminishes in height with distance from the grounding line and is hence not a destabilizing factor for ice shelves.</p

The marine and continental cryosphere in NW Greenland : holocene dynamics under a changing climate and interplay with the oceanographic context

Thèse en cotutelle : Université Laval, Québec, Canada et Université de Bordeaux, Talence, FranceLe détroit de Nares constitue l'un des trois domaines de l'Archipel Arctique Canadien (AAC) reliant l'océan Arctique à la baie de Baffin. Le potentiel d'eau douce transporté via ces détroits atteint, au sud de la baie de Baffin, la mer du Labrador, et module ainsi les caractéristiques physico-chimiques des eaux de surface et de sub-surface de cette région, siège de la formation d'une des composantes majeures de la circulation profonde de l'Atlantique Nord. Le détroit de Nares, à la frontière est de l'AAC, est à 80% couvert de glace de mer pendant 11 mois de l'année sous l'influence (1) de l'apport de banquise multi-annuelle provenant de l'océan Arctique au Nord, et (2) de la formation in situ de glace de mer. L'histoire hydrologique de cette région est donc intimement liée à celle de ces deux composantes. Par ailleurs, ce couvert de glace régule le transport d'eaux dessalées et de glace vers la baie de Baffin, et entretient l'existence d'une zone ouverte : la polynie des eaux du nord. La polynie des eaux du nord est aujourd'hui essentiellement une polynie à chaleur latente. L'arc de glace du bassin de Kane empêche la dérive de glace de mer et d'icebergs vers la baie de Baffin, pendant que les vents puissants chassent la glace formée à la surface de la polynie. Deux processus physiques important ont alors lieu : (1) la formation de glace de mer en continue entretient la formation de saumures ou « brines », des eaux salées et froides, et (2) sous l'effet du vent, les masses d'eaux de surface sont déviées vers l'île d'Ellesmere. Un mouvement vertical est initié par la plongée des brines et le pompage d'Ekman résultant du déplacement des masses d'eaux par le vent induit la remontée d'eaux atlantiques chaudes, riches en nutriments. La remontée d'eaux atlantiques peut promouvoir la fonte de la glace en surface, ce qui confère à la polynie des eaux du nord son caractère sensible. La productivité primaire est alimentée en continu par des eaux pacifiques riches en silicates à travers le détroit de Nares et la remontée d'eaux atlantiques riches en nitrates dans la polynie, jusqu'à la rupture estivale du pont de glace qui entraine l'entrée de glace dans la polynie et l'arrêt de la remontée de nitrates. Depuis les années 1980, la durée moyenne du pont de glace est en diminution, engendrant une chute de la productivité. Le détroit de Nares a été affecté durant la période post-glaciaire par (1) un retrait rapide des calottes groenlandaise et innuitienne, initialement ancrées sur le fond et convergeant au niveau du détroit de Nares, (2) une baisse importante du niveau marin (rebond isostatique) et (3) des conditions variables de glace de mer pérenne ou saisonnière. Ces trois phénomènes, dont la chronologie et le synchronisme à l'échelle régionale sont très mal contraints, font du détroit de Nares un domaine unique d'examen de la réponse de la cryosphère marine et continentale à un changement climatique rapide tel celui amplifié aujourd'hui dans les régions arctiques sous le forçage du réchauffement global. Les archives sédimentaires prélevées lors des campagnes (2014 et 2016) du NGCC Amundsen dans le cadre de l'ANR GreenEdge et du programme canadien ArcticNet offrent une opportunité unique de reconstituer l'histoire post-glaciaire à tardi-holocène de la région. Notre travail repose sur une analyse multi-proxies de ces archives incluant pour chaque carotte une étude sédimentologique approfondie (granulométrie et lithofaciès), une analyse micropaléontologique (assemblages de foraminifères benthiques et planctoniques), des mesures géochimiques continues de la distribution d'éléments majeurs et mineurs (banc XRF core-scanner), des analyses minéralogiques (q-XRD) et des mesures biogéochimiques (biomarqueurs de la glace de mer IP25 et HBI III). Nos résultats nous ont amené à proposer un âge d'ouverture pour le détroit de Nares situé entre 9 et 8.3 mille ans avant l'actuel (cal. ka BP), avec un âge probable autour de 8.5-8.3 cal. ka BP. Les conditions environnementales suivant la connexion de l'océan Arctique avec la baie de Baffin ont été très variables en lien avec le maximum thermique holocène (induisant de très fortes températures atmosphériques) et l'apport important d'eau de fonte lié au recul des calottes. Dans un environnement plus glacio-distal, un minimum de couvert de glace de mer est observé entre 8.1 et 7.5 cal. ka BP. Avec la chute de températures atmosphériques, le couvert de glace de mer saisonnière est établi de façon régulière à partir de 7.5 cal. ka BP, mais ce n'est qu'à partir de 5.5 cal. ka BP que le pont de glace du bassin de Kane s'inscrit durablement au printemps et en été. La polynie est initiée à partir de 5.5 cal. ka BP, mais elle repose sur une chaleur essentiellement latente. Ce n'est qu'à partir de 4.5 cal. ka BP, lorsque les températures atmosphériques sont assez froides, que la formation de brines est assez importante pour engendrer le transport vertical d'eaux atlantiques. A partir de 3.7/3.0 cal. ka BP, le pont de glace nord est présent de façon quasi-pérenne, ce qui empêche l'entrée de glace de mer arctique épaisse dans le détroit de Nares et abouti à la fragilisation du pont de glace dans le bassin de Kane. Le détroit de Nares devient libre de glace de façon saisonnière et, du fait de l'absence de convection, les eaux de la région nord de la baie de Baffin deviennent stratifiées. Le rétablissement du pont de glace du bassin de Kane est limité à une courte période centrée autour de 500 ans avant l'actuel.Nares Strait is one of three channels of the Canadian Arctic Archipelago (CAA) which connect the Arctic Ocean to Baffin Bay. The CAA throughflow is a major component of ocean circulation in western Baffin Bay. Nares Strait borders the CAA to the east, separating Ellesmere Island from Greenland, and is 80% covered in sea ice 11 months of the year. The heavy sea ice cover is constituted of (1) Arctic (multi-year) sea-ice having entered the strait by the north, and (2) locally formed first year sea ice, which consolidates the ice cover. The hydrological history of the area is intimately linked to the formation of land-fast sea ice in the strait, constituting ice arches. The seaice cover in Nares Strait regulates freshwater (liquid and solid) export towards Baffin Bay, and is integral to the formation of an area of open water in northernmost Baffin Bay: The North Water polynya. Nares Strait has been at the heart of major geomorphological changes over the past 10,000 years. Its deglacial and post-glacial history is marked by (1) rapid retreat of the Greenland and Innuitian ice-sheets which coalesced along Nares Strait during the Last Glacial Maximum, (2) post-glacial shoaling associated to isostatic rebound, and (3) variable multi-year and seasonal sea ice conditions. Little is known about the evolution of these three environmental components of the Nares Strait history, and they are poorly constrained in terms of chronology and synchronism with other regional changes. Nares Strait and its eventful Holocene history provide a unique case study of the response of the marine and continental cryosphere to rapid climate change, such as that affecting Arctic regions in modern times. The marine sediment archives that were retrieved during the ANR GreenEdge and ArcticNet (2014 and 2016) cruises of CCGS Amundsen offer a unique opportunity to investigate the Deglacial to Late Holocene history of Nares Strait. Our reconstructions are based on a multi-proxy study of these cores, including sedimentologic (grain size and lithofacies), geochemical (XRF), mineralogical (q-XRD), micropaleontological (planktic and benthic foraminiferal assemblages), and biogeochemical (sea ice biomarkers IP25 and HBI III). Our results include an age for the Deglacial opening of Nares Strait between 9.0 and 8.3 cal. ka BP, with the event likely occurring closer to the later bracket of the timeframe (i.e., ca 8.5-8.3 cal. ka BP). This event established the throughflow from the Arctic Ocean towards northernmost Baffin Bay. Environmental conditions were highly unstable in the Early Holocene, and marine primary productivity was limited. A period of minimum sea-ice cover occurred from ca 8.1 to 7.5 cal. ka BP, during the Holocene Thermal Maximum, when atmospheric temperatures were higher than today in Nares Strait. Sea-ice cover became more stably established as a seasonal feature around 7.5 cal. ka BP and primary productivity related to ice edge blooms increased. Eventually, the duration of the ice arches increased and they were present in spring and into the summer from 5.5 to 3.7 cal. ka BP, which allowed the inception of the North Water polynya. The North Water reached its maximal potential between 4.5 and 3.7 cal. ka BP, when warmer Atlantic-sourced water upwelled in the polynya, providing nutrients for primary productivity. The establishment of a near-perennial ice arch in northern Nares Strait prevented export of multi-year sea ice into Nares Strait and hindered the formation of the southern ice arch, ultimately resulting in a less productive polynya over the past ca 3.0 cal. ka BP

Empirical Removal of Tides and Inverse Barometer Effect on DInSAR From Double DInSAR and a Regional Climate Model

Ice shelves-the floating extensions of the Antarctic ice sheet-regulate the Antarctic contribution to sea-level rise by restraining the grounded ice flowing from upstream. Therefore, ice-shelf change (e.g., ice-shelf thinning) results in accelerated ice discharge into the ocean, which has a direct effect on sea level. Studying ice-shelf velocity allows the monitoring of the ice shelves' stability and evolution. Differential synthetic aperture radar interferometry (DInSAR) is a common technique from which highly accurate velocity maps can be inferred at high resolution. Because ice shelves are afloat, small sea-level changes-i.e., ocean tides and varying atmospheric pressure (aka inverse barometer effect) lead to vertical displacements. If not accounted for in the interferometric process, these effects will induce a strong bias in the horizontal velocity estimation. In this article, we present an empirical DInSAR correction technique from geophysical models and double DInSAR, with a study on its variance propagation. The method is developed to be used at large coverage on short timescales, essential for the near-continuous monitoring of rapidly changing areas on polar ice sheets. We used Sentinel-1 SAR acquisitions in interferometric wide and extra -wide swath modes. The vertical interferometric bias is estimated using a regional climate model (MAR) and a tide model (CATS2008). The study area is located on the Roi Baudouin Ice Shelf in Dronning Maud Land, East Antarctica. Results show a major decrease (67 m·a -1 ) in the vertical-induced displacement bias.Fil: Glaude, Quentin. Université Libre de Bruxelles; Bélgica. Université de Liège; BélgicaFil: Amory, Charles. Universite de Liege. Faculty Of Applied Sciences.; BélgicaFil: Berger, Sophie. Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung; Alemania. Université Libre de Bruxelles; BélgicaFil: Derauw, Dominique Maurice. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pattyn, Frank. Vrije Unviversiteit Brussel; Bélgica. Université Libre de Bruxelles; BélgicaFil: Barbier, Christian. Université de Liège; BélgicaFil: Orban, Anne. Université Catholique de Louvain; Bélgic

The historical Greenland Climate Network (GC-Net) curated and augmented level-1 dataset

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, atmospheric pressure, downward and reflected shortwave irradiance, net radiation, and ice and firn temperatures. The majority of the GC-Net sites were located in the ice sheet accumulation area (17 AWSs), while 11 AWSs were located in the ablation area, and two sites (three AWSs) were located close to the equilibrium line altitude. Additionally, three AWSs of similar design to the GC-Net AWS were installed by Konrad Steffen's team on the Larsen C ice shelf, Antarctica. After more than 3 decades of operation, the GC-Net AWSs are being decommissioned and replaced by new AWSs operated by the Geological Survey of Denmark and Greenland (GEUS). Therefore, making a reassessment of the historical GC-Net AWS data is necessary. We present a full reprocessing of the historical GC-Net AWS dataset with increased attention to the filtering of erroneous measurements, data correction and derivation of additional variables: continuous surface height, instrument heights, surface albedo, turbulent heat fluxes, and 10 m ice and firn temperatures. This new augmented GC-Net level-1 (L1) AWS dataset is now available at https://doi.org/10.22008/FK2/VVXGUT (Steffen et al., 2023) and will continue to be refined. The processing scripts, latest data and a data user forum are available at https://github.com/GEUS-Glaciology-and-Climate/GC-Net-level-1-data-processing (last access: 30 November 2023). In addition to the AWS data, a comprehensive compilation of valuable metadata is provided: maintenance reports, yearly pictures of the stations and the station positions through time. This unique dataset provides more than 320 station years of high-quality atmospheric data and is available following FAIR (findable, accessible, interoperable, reusable) data and code practices.</p