Preprints
https://doi.org/10.5194/egusphere-2023-1320
https://doi.org/10.5194/egusphere-2023-1320
28 Jul 2023
 | 28 Jul 2023

Extreme melting at Greenland’s largest floating ice tongue

Ole Zeising, Niklas Neckel, Nils Dörr, Veit Helm, Daniel Steinhage, Ralph Timmermann, and Angelika Humbert

Abstract. The 79° North Glacier (Nioghalvfjerdsbrae, 79NG) is one of three remaining glaciers with a floating tongue in Greenland. Although the glacier was considered exceptionally stable in the past, earlier studies indicate that the ice tongue has thinned in recent decades. By conducting high-resolution ground-based and airborne radar measurements in conjunction with satellite remote sensing observations, we find significant changes in the geometry of 79NG. In the vicinity of the grounding line, a 500 m high subglacial channel has grown since ~2010 and caused surface lowering of up to 7.6 m a-1. Our results show extreme basal melt rates exceeding 150 m a-1 within a distance of 5 km from the grounding line, where the ice has thinned by 42 % since 1998. We found a heterogeneous distribution of melt rates likely due to variability in water column thickness and channelization of the ice base. Time series of melt rates show a decrease in basal melting since 2018, indicating an inflow of colder water into the cavity below 79NG. We discuss the processes that have led to the changes in geometry and conclude that the inflow of warm ocean currents has led to the extensive thinning of 79NG's floating ice tongue near the grounding line in the last two decades. In contrast, we hypothesize that the growth of the channel results from increased subglacial discharge due to a considerably enlarged area of summer surface melt due to the warming of the atmosphere.

Ole Zeising, Niklas Neckel, Nils Dörr, Veit Helm, Daniel Steinhage, Ralph Timmermann, and Angelika Humbert

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1320', Anonymous Referee #1, 31 Aug 2023
    • AC1: 'Reply on RC1', Ole Zeising, 15 Sep 2023
  • RC2: 'Comment on egusphere-2023-1320', Christoph Mayer, 04 Sep 2023
    • AC2: 'Reply on RC2', Ole Zeising, 15 Sep 2023

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1320', Anonymous Referee #1, 31 Aug 2023
    • AC1: 'Reply on RC1', Ole Zeising, 15 Sep 2023
  • RC2: 'Comment on egusphere-2023-1320', Christoph Mayer, 04 Sep 2023
    • AC2: 'Reply on RC2', Ole Zeising, 15 Sep 2023
Ole Zeising, Niklas Neckel, Nils Dörr, Veit Helm, Daniel Steinhage, Ralph Timmermann, and Angelika Humbert
Ole Zeising, Niklas Neckel, Nils Dörr, Veit Helm, Daniel Steinhage, Ralph Timmermann, and Angelika Humbert

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Latest update: 21 Feb 2024
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This study addresses an important question regarding the stability of ice shelves, a question that is highly relevant for Greenland and Antarctica. Using a unique combination of observations, the authors document extensive thinning and extremely high basal melt rates at the floating tongue Nioghalvfjerdsbræ, North Greenland, an important and fast-changing part of the Greenland Ice Sheet. The increase in melt rates are suggested to be caused by an increase in surface melt that is funneling surface water under the ice shelf.
Short summary
The 79° North Glacier in Greenland is experiencing significant changes in the last decades. Due to extreme melt rates, the ice has thinned significantly in vicinity of the grounding line where a large subglacial channel has formed since 2010. We attribute these changes to warm ocean currents and an increased subglacial discharge from surface melt. However, basal melting has decreased since 2018, indicating colder water inflow into the cavity below the glacier.