Oceanic and climatic impacts of freshwater release over the last few decades (D3.4)

• Main Authors: Swingedouw, Didier, Herbaut, Christophe, Garric, Gilles, Devilliers, Marion, Mignot, Juliette, Houssais, Marie-Noelle, Blaizot, Anne-Cecile
• Format: Report
• Language: English
• Published: Zenodo 2019
• Subjects: Greenland; Ice Sheet; North Atlantic; Sea ice
• Online Access: https://doi.org/10.5281/zenodo.3559468

Summary: The Greenland ice sheet has been melting at an increasing rate for the last few decades. Large rates of melting have also been reported to have occurred in the 1920s, due to a warming of the region during this decade. Recent reconstructions of the ocean circulation in the North Atlantic have suggested that the large-scale overturning circulation might have been reduced over the last century, possibly due to the freshwater released by Greenland ice sheet melting. To evaluate this hypothesis, we have conducted a series of ocean-only and fully-coupled climate simulations where we include or exclude the observed melting of Greenland ice sheet, which is usually neglected in climate simulations of the last century. Based on a recent estimate of the Greenland ice sheet melting, we have constructed a forcing melting field for the ~100 km resolution IPSL-CM6A-LR climate model (including ocean, atmosphere land and sea ice), and also for a ~2-3 km NEMO regional coupled sea ice-ocean model. The use of two different resolutions for the ocean allows us to evaluate the importance of small-scale oceanic processes for the impact of the Greenland ice sheet melting. We have then integrated these two types of models over two different time periods: 1920-2014 for the climate model, with 10 different members to account for the potential role of intrinsic variability of the climate, and 2004-2017 for the high-resolution ocean-only model, due to its high cost in terms of computing time. We have considered two types of simulations: one where the freshwater release from Greenland ice sheet is computed within the climate model (through a basic freshwater closure) and the other where we apply time-varying observation-based estimates. The main results highlight several crucial insights. First, the climate model simulations show that the observation-based melting of Greenland ice sheet, even if it has a modest amplitude, does have a significant impact on the state of the North Atlantic, and even induces a slight reduction of the ...