Ocean melting of the Zachariae Isstrøm and Nioghalvfjerdsfjorden glaciers, northeast Greenland

Lu An (1) , Eric Rignot (1, 2) , Michael Wood (1, 2) , Josh Willis (2) , Jérémie Mouginot (3, 1) , Shfaqat Khan (4)

1 UC Irvine - University of California [Irvine]
2 JPL - Jet Propulsion Laboratory
3 IGE - Institut des Géosciences de l’Environnement
4 DTU - Danmarks Tekniske Universitet = Technical University of Denmark

Zachariae Isstrøm (ZI) and Nioghalvfjerdsfjorden (79N) are marine-terminating glaciers in northeast Greenland that hold an ice volume equivalent to a 1.1-m global sea level rise. ZI lost its floating ice shelf, sped up, retreated at 650 m/y, and experienced a 5-gigaton/y mass loss. Glacier 79N has been more stable despite its exposure to the same climate forcing. We analyze the impact of ocean thermal forcing on the glaciers. A three-dimensional inversion of airborne gravity data reveals an 800-m-deep, broad channel that allows subsurface, warm, Atlantic Intermediate Water (AIW) (+1. 25 ○ C) to reach the front of ZI via two sills at 350-m depth. Subsurface ocean temperature in that channel has warmed by 1.3 ± 0 . 5 ○ C since 1979. Using an ocean model, we calculate a rate of ice removal at the grounding line by the ocean that increased from 108 m/y to 185 m/y in 1979–2019. Observed ice thinning caused a retreat of its flotation line to increase from 105 m/y to 217 m/y, for a combined grounding line retreat of 13 km in 41 y that matches independent observations within 14%. In contrast, the limited access of AIW to 79N via a narrower passage yields lower grounded ice removal (53 m/y to 99 m/y) and thinning-induced retreat (27 m/y to 50 m/y) for a combined retreat of 4.4 km, also within 12% of observations. Ocean-induced removal of ice at the grounding line, modulated by bathymetric barriers, is therefore a main driver of ice sheet retreat, but it is not incorporated in most ice sheet models.

Mots clés: Greenland; glaciology; sea level; ice–ocean interaction; climate

Domaines: Glaciologie; Océanographie

Lu An, Eric Rignot, Michael Wood, Josh Willis, Jérémie Mouginot, et al.. Ocean melting of the Zachariae Isstrøm and Nioghalvfjerdsfjorden glaciers, northeast Greenland. Proceedings of the National Academy of Sciences of the United States of America, 2021, 118 (2), pp.e2015483118. ⟨10.1073/pnas.2015483118⟩. ⟨hal-03403514⟩