The Northeast Greenland Ice Stream triggered past ice-surface elevation changes in central Greenland

A Glimpse into the Past
Greenland ice sheet holds a wealth of information about Earth’s climatic history. By studying ice cores – cylinders of ice drilled from the ice sheet – scientists can extract valuable data on past ice accumulation and melt rates, past air temperature and greenhouse gas concentrations spanning thousands of years. Ice cores also reveal changes in surface elevation at drilling sites, indicating that since the beginning of the Holocene (~11,700 years ago), Greenland’s surface elevation has significantly dropped, with hundreds of meters of thinning observed across the ice sheet (Vinther et al., 2009). Interestingly, three-dimensional ice sheet models, which can reconstruct past ice-sheet behavior, struggle to reproduce such a thinning, especially in central Greenland. This discrepancy raises questions about the accuracy of these models and reconstructions from ice cores. 
The Role of the Northeast Greenland Ice Stream (NEGIS). 
The Northeast Greenland Ice Stream (NEGIS) is currently the largest ice stream in Greenland, spanning approximately 600 km and extending far inland to the ice divide. Evidence of a similar stream during the early Holocene and the existence of a now-extinct northern tributary (Franke et al., 2022) suggest that the paleo NEGIS might have influenced the ice-sheet dynamics during the Holocene. Despite this, most current models fail to accurately reproduce NEGIS-like dynamics, hindering a full assessment of its impact. 
The new study from Tabone et al. (2024), published in Nature Communications, examines the effects of the Northeast Greenland retreat on ice-sheet dynamics during the Holocene. Using a large ensemble of simulations with a three-dimensional ice-sheet model (Robinson et al., 2020), the research reveals that the  early Holocene retreat in Northeast Greenland triggered changes in ice elevation at the ice divide through changes in the ice dynamics. The process behind this is quite simple: at the onset of the Holocene, the northeast margin of the ice sheet retreated due to rising temperatures. This retreat led to upstream velocity propagation along the paleo NEGIS, driven by increased subglacial water production and enhanced sliding at the ice base, resulting in extensive dynamic effects on the interior of the ice sheet. This finding highlights the significant role of the NEGIS dynamics in shaping the ice sheet’s past evolution.
Implications for Future Research
This study represents a significant advancement in understanding the processes that controlled the thinning of the Greenland ice sheet during the last deglaciation. Moreover, it provides crucial insights into the role of the NEGIS in the context of current climate warming. Since most ice-sheet models do not accurately represent the current velocity pattern of the NEGIS, the findings suggest that the extent of dynamic thinning in north-central Greenland may be underestimated in future projections. By incorporating the ice stream dynamics more accurately into numerical models, the accuracy of both past reconstructions and future projections can be improved. This has profound implications for understanding ice-sheet stability and its contribution to sea-level rise in a warming world.

References
Vinther, B. et al. Holocene thinning of the Greenland ice sheet. Nature 461, 385–388 (2009).
Franke, S. et al. Holocene ice-stream shutdown and drainage basin reconfiguration in northeast Greenland. Nat. Geosci. 15, 995–1001 (2022). 

Tabone, I. et al. Holocene thinning in central Greenland controlled by the Northeast Greenland Ice Stream. Nat Commun 15, 6434 (2024). https://doi.org/10.1038/s41467-024-50772-5

Robinson, A. et al. Description and validation of the ice-sheet model Yelmo (version 1.0). Geosci. Model. Dev. 13, 2805–2823 (2020).