Abstract
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.
Highlights
The East Greenland Ice-core Project (EastGRIP) is the first attempt to retrieve a deep ice core inside an active ice stream
The drill site is located in the upstream part of the Northeast Greenland Ice Stream (NEGIS; Fahnestock et al, 1993), which is a substantial contributor to the Greenland Ice Sheet (GrIS) mass balance (Khan et al, 2014) and accounts for around 12 % of its total ice discharge (Rignot and Mouginot, 2012)
Particle trajectories were calculated from the simulated velocity field with the mean model parameters and indicate the source location of ice found at the modelled isochrone depth in the EastGRIP ice core
Summary
The East Greenland Ice-core Project (EastGRIP) is the first attempt to retrieve a deep ice core inside an active ice stream. The drill site is located in the upstream part of the Northeast Greenland Ice Stream (NEGIS; Fahnestock et al, 1993), which is a substantial contributor to the Greenland Ice Sheet (GrIS) mass balance (Khan et al, 2014) and accounts for around 12 % of its total ice discharge (Rignot and Mouginot, 2012). Large-scale ice-sheet models are essential tools to anticipate the future development of the NEGIS and its potential impact on the stability of the GrIS (Joughin et al, 2001; Khan et al, 2014; Vallelonga et al, 2014). The high ice-flow velocities in the upstream area of the NEGIS and the clearly defined shear margins are difficult to reproduce with ice-flow models (Beyer et al, 2018). A recent study by Smith-Johnsen et al (2020a) showed that the high surface velocities in the onset region of the ice stream could be reproduced with their model, using an exceptionally
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
