A first chronology for the East Greenland Ice-core Project (EGRIP) over the Holocene and last glacial termination

Mojtabavi, Seyedhamidreza; Wilhelms, Frank; Cook, Eliza; Davies, Siwan M.; Sinnl, Giulia; Jensen, Mathias Skov; Dahl-Jensen, Dorthe; Svensson, Anders; Vinther, Bo M.; Kipfstuhl, Sepp; Jones, Gwydion; Karlsson, Nanna B.; Faria, Sérgio H.; Gkinis, Vasileios; Kjær, Helle Astrid; Erhardt, Tobias; Berben, Sarah M P; Nisancioglu, Kerim H.; Koldtoft, Iben; Rasmussen, Sune Olander

doi:10.5194/cp-16-2359-2020

Cited by 44 publications

(34 citation statements)

References 37 publications

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“…Variability between samples from similar depths is small below 1200 m. NEEM grain size increases until a depth of 740 m and is rather stable until 1350 m even though grain size variability is extreme such that is varies for several square millimetres between samples from similar depths. The cores are roughly 450 km apart but show a similar depth-age relationship in the investigated depth range: the Glacial-Holocene transition is at 1375 m of depth at EGRIP (Mojtabavi et al, 2020) and at 1420 m at NEEM (Rasmussen et al, 2013). The ice stream thus seems to have an impact on grain growth via dynamic recrystallisation in the upper several hundreds of metres.…”

Section: Discussionmentioning

confidence: 71%

“…At EGRIP the brittle ice zone is between 550 and 1000 m of depth according to visual stratigraphy and the core break record. Following Walker et al (2018) the Holocene (present-11.7 ka) is in the upper 1240 m, the Younger Dryas (11.7-12.8 ka) at 1240-1280 m, and the Bølling Allerød (12.8-14.7 ka) at 1280-1375 m (Mojtabavi et al, 2020). We focus on the analysis of the upper 1340 m in this study.…”

Section: The East Greenland Ice Core Projectmentioning

confidence: 99%

“…The nine shallower samples are from the Holocene, and the deepest sample is from the last glacial termination, i.e. the Bølling Allerød (Mojtabavi et al, 2020).…”

Section: Sample Choice and Preparationmentioning

confidence: 99%

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Microstructure, micro-inclusions, and mineralogy along the EGRIP ice core – Part 1: Localisation of inclusions and deformation patterns

et al. 2021

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Abstract. Impurities deposited in polar ice enable the reconstruction of the atmospheric aerosol concentration of the past. At the same time they impact the physical properties of the ice itself such as its deformation behaviour. Impurities are thought to enhance ice deformation, but observations are ambiguous due to a shortage of comprehensive microstructural analyses. For the first time, we systematically analyse micro-inclusions in polar fast flowing ice, i.e. from the East Greenland Ice Core Project ice core drilled through the Northeast Greenland Ice Stream. In direct relation to the inclusions we derive the crystal preferred orientation, fabric, grain size, and microstructural features at 10 depths, covering the Holocene and Late Glacial. We use optical microscopy to create microstructure maps to analyse the in situ locations of inclusions in the polycrystalline, solid ice samples. Micro-inclusions are more variable in spatial distribution than previously observed and show various distributional patterns ranging from centimetre-thick layers to clusters and solitary particles, independent of depth. In half of all samples, micro-inclusions are more often located at or close to the grain boundaries by a slight margin (in the areas occupied by grain boundaries). Throughout all samples we find strong indications of dynamic recrystallisation, such as grain islands, bulging grains, and different types of sub-grain boundaries. We discuss the spatial variability in micro-inclusions, the link between spatial variability and mineralogy, and possible effects on the microstructure and deformation behaviour of the ice. Our results emphasise the need for holistic approaches in future studies, combining microstructure and impurity analysis.

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Section: Discussionmentioning

confidence: 71%

Section: The East Greenland Ice Core Projectmentioning

confidence: 99%

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Microstructure, micro-inclusions, and mineralogy along the EGRIP ice core – Part 1: Localisation of inclusions and deformation patterns

et al. 2021

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“…To account for any differences in surface elevation or topography between RES data from different years, the ice surface reflections of the radar profiles were aligned to the surface elevation from ArcticDEM (Porter et al, 2018). The bed topography in the data gaps of the profiles was derived from the BedMachine v3 data set (Morlighem et al, 2017).…”

Section: Eastgrip Flow Linesmentioning

confidence: 99%

Upstream flow effects revealed in the EastGRIP ice core using Monte Carlo inversion of a two-dimensional ice-flow model

et al. 2021

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Abstract. The Northeast Greenland Ice Stream (NEGIS) is the largest active ice stream on the Greenland Ice Sheet (GrIS) and a crucial contributor to the ice-sheet mass balance. To investigate the ice-stream dynamics and to gain information about the past climate, a deep ice core is drilled in the upstream part of the NEGIS, termed the East Greenland Ice-core Project (EastGRIP). Upstream flow can introduce climatic bias into ice cores through the advection of ice deposited under different conditions further upstream. This is particularly true for EastGRIP due to its location inside an ice stream on the eastern flank of the GrIS. Understanding and ultimately correcting for such effects requires information on the atmospheric conditions at the time and location of snow deposition. We use a two-dimensional Dansgaard–Johnsen model to simulate ice flow along three approximated flow lines between the summit of the ice sheet (GRIP) and EastGRIP. Isochrones are traced in radio-echo-sounding images along these flow lines and dated with the GRIP and EastGRIP ice-core chronologies. The observed depth–age relationship constrains the Monte Carlo method which is used to determine unknown model parameters. We calculate backward-in-time particle trajectories to determine the source location of ice found in the EastGRIP ice core and present estimates of surface elevation and past accumulation rates at the deposition site. Our results indicate that increased snow accumulation with increasing upstream distance is predominantly responsible for the constant annual layer thicknesses observed in the upper part of the ice column at EastGRIP, and the inverted model parameters suggest that basal melting and sliding are important factors determining ice flow in the NEGIS. The results of this study form a basis for applying upstream corrections to a variety of ice-core measurements, and the inverted model parameters are useful constraints for more sophisticated modelling approaches in the future.

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“…A GB =accumulated area occupied by grain boundaries, R GB =ratio of grain boundary area to percentage of micro-inclusions at grain boundaries, b2k=before 2000 (Mojtabavi et al, 2020) at depths of 415.3, 757.21 and 1062.65 m, respectively. The deepest sample from a depth of 1339.75 m showed the highest amount of micro-inclusions at grain boundaries (42.4%) and the largest area occupied by grain boundaries (43.2%) as here we have the smallest grain size of all inspected samples (Fig.…”

Section: Micro-inclusions At Grain Boundariesmentioning

confidence: 99%

Microstructure, Micro-inclusions and Mineralogy along the EGRIP ice core – Part 1: Localisation of inclusions and deformation patterns

Stoll

Eichler

Hörhold

et al. 2021

Preprint

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Abstract. Impurities deposited in polar ice allow the reconstruction of the atmospheric aerosol concentration of the past. At the same time they impact the physical properties of the ice itself such as its deformation behaviour. Impurities are thought to enhance ice deformation, but observations are ambiguous due to a shortage of comprehensive microstructural analyses. For the first time, we systematically analyse micro-inclusions in polar fast flowing ice, i.e. from the East Greenland Ice Core Project ice core drilled trough the Northeast Greenland Ice Stream. In direct relation to the inclusions we derive the crystal-preferred orientation, fabric, grain size, and microstructural features at ten depths, covering the Holocene and Late Glacial. We use optical microscopy to create microstructure maps to analyse the in situ locations of inclusions in the polycrystalline, solid ice samples. Micro-inclusions are more variable in spatial distribution than previously observed, and show various distributional patterns ranging from centimetre-thick layers to clusters and solitary particles, independent of depth. Analysing the area occupied by grain boundaries in the respective samples shows that micro-inclusions are slightly more often located at or close to grain boundaries in half of all samples. Throughout all samples we find strong indications of dynamic recrystallisation, such as grain islands, bulging grains and different types of subgrain boundaries. We discuss the spatial variability of micro-inclusions, the link between spatial variability and mineralogy, and possible effects on the microstructure and deformation behaviour of the ice. Our results emphasise the need for holistic approaches in future studies, combining microstructure and impurity analysis.

show abstract

A first chronology for the East Greenland Ice-core Project (EGRIP) over the Holocene and last glacial termination

Cited by 44 publications

References 37 publications

Microstructure, micro-inclusions, and mineralogy along the EGRIP ice core – Part 1: Localisation of inclusions and deformation patterns

Microstructure, micro-inclusions, and mineralogy along the EGRIP ice core – Part 1: Localisation of inclusions and deformation patterns

Upstream flow effects revealed in the EastGRIP ice core using Monte Carlo inversion of a two-dimensional ice-flow model

Microstructure, Micro-inclusions and Mineralogy along the EGRIP ice core – Part 1: Localisation of inclusions and deformation patterns

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