Greenland ice-sheet melt exciting ocean extremes (G-shocx)

• Applicant: Dr. Torge Martin
• Subject Area: Oceanography
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 431440277

• Final Report Year: 2024

Final Report Abstract

For more than two decades the Greenland ice sheet mass balance was negative in each single year. Liquid meltwater runoff and solid ice discharge from the ice sheet into the surrounding ocean has increased by 40-50% from the late 1990s to the 2010s. As the ice sheet is anticipated to decay with an accelerating rate under global warming, much faster than it can reaccumulate, this has been identified as a tipping element in the climate system. Moreover, the freshwater that is added in consequence to the subpolar North Atlantic may critically reduce upper ocean density, which would limit the formation of dense water masses in the subpolar North Atlantic. Massive cooling of the ocean at subpolar latitudes leads to the sinking of surface waters to depths of 1000-2000 m in the ocean near Greenland. This so-called overturning is— as its name says—a major driver of the Atlantic Meridional Overturning Circulation (AMOC). The AMOC is an important component in the northward transport of heat making northern Europe a habitable place even at high latitudes. The AMOC is also identified as another tipping element in the climate system as it does not respond linearly to drastic freshwater forcing in climate model simulations. The goal of the G-shocx project was to identify a potential emergence of impacts by the strongly enhanced mass loss of the Greenland ice sheet on the surrounding ocean and to investigate whether extreme runoff could also trigger ocean extremes. This meant to study salinity anomalies on the Greenland shelf on two different, monthly to interannual and decadal time scales. In a first study, we analyzed the East Greenland Current (EGC) system for magnitude, pathways and propagation times of salinity anomalies. In brief, the study demonstrates that (1) extreme runoff anomalies, such as in 2010 and 2012, only show in the coastal part of the EGC as pronounced salinity anomaly but are quickly diluted offshore and (2) strong anomalies in sea ice melt and wind can cause salinity anomalies of similar or stronger magnitude as runoff. With respect to a potential imprint on the deep water formation, wind events are found to be dominant and runoff extremes are only exported from the boundary to the interior with coinciding, favorable winds. A pair of dedicated model experiments presented in a second paper served to identify imprints of enhanced Greenland melt on the regional ocean. Comparing two simulations with an eddy-rich 1/20˚ ocean/sea-ice model, one with realistically increased Greenland runoff after 1997 and one with maintained lower 20th century climatological runoff, demonstrates that (1) the boundary current is accelerating, (2) Labrador Sea deep convection is reduced, and (3) deep convection in the Irminger Sea is intensified and shifted farther to the east. The AMOC, however, does not (yet) show any imprint of these changes.

Publications

• Do salinity variations along the East Greenland shelf show imprints of increasing meltwater runoff?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5135. abstract / talk
  Schiller-Weiss, T. Martin, A. Biastoch & J. Karstensen
  
• Do salinity variations along the East Greenland shelf show imprints of increasing meltwater runoff? DRAKKAR workshop, Grenoble, France, 30 Jan–1 Feb 2023
  Schiller-Weiss, T. Martin J. Karstensen & A. Biastoch
  
• Do Salinity Variations Along the East Greenland Shelf Show Imprints of Increasing Meltwater Runoff?. Journal of Geophysical Research: Oceans, 128(10).
  Schiller‐Weiss, Ilana; Martin, Torge; Karstensen, Johannes & Biastoch, Arne
  
• Does freshwater content of the East Greenland Current show imprints of increasing meltwater runoff? EGU General Assembly 2023, Vienna, Austria, 23–28 April 2023, EGU23-6219. abstract / poster
  Schiller-Weiss, T. Martin J. Karstensen & A. Biastoch
  
• Emerging impacts of enhanced Greenland melting on Labrador Sea dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024. abstract / talk
  Schiller-Weiss, I., Martin, T. & F. Schwarzkopf
  
• Emerging Influence of Enhanced Greenland Melting on Boundary Currents and Deep Convection Regimes in the Labrador and Irminger Seas. Geophysical Research Letters, 51(9).
  Schiller‐Weiss, Ilana; Martin, Torge & Schwarzkopf, Franziska U.
  
• Enhanced Greenland Meltwater Impacts on Labrador Sea Dynamics, DRAKKAR workshop, Grenoble, France, 29–31 Jan 2024.
  Schiller-Weiss, T. Martin & F. Schwarzkopf