Recent evolution of the greenlandic ice shelves 

Abstract

<div>In the northern parts of Greenland, which hold more than 2.7 m of sea level equivalent, the ice flows through ice shelves, as in Antarctica. These floating platforms are the vulnerable parts of the ice sheets because they are the first element in contact with the warming ocean waters. Indeed, the advection of warm, salty ocean waters beneath the ice shelves increases basal melting, which reduces the buttressing effect of the ice shelves and can, in turn, trigger an increase in ice flow into the ocean. </div><div> </div><div>Indeed, It has been observed that Zachariae Isstrøm in northeast Greenland is retreating and accelerating, most likely due to increased melting of the base of its ice shelf, followed by breakup. Nioghalvfjerdsfjorden, its neighbor, also shows signs of thinning near its grounding line, as does Petermann Gletscher, 800 km further west. Here we study the recent dynamic and geometric changes of all present and former ice shelves along the north coast of Greenland, namely Humboldt Gletscher, Steensby Gletscher, Ryder Gletscher, Ostenfeld Gletscher, Marie Sophie Gletscher, Academy Gletscher and Hagen Bræ.</div><div> </div><div>We document the evolution of ice shelf surface elevation using data from the Greenland Ice Mapping Project, NASA's ICESat-½, NASA's ATM, LVIS and Ocean Melting Greenland instruments. In addition, we generate digital elevation models using stereo images acquired by ASTER for all ice shelves between 2000 and the present. For the same time period, surface ice velocity is also derived from multiple optical (Landsat-7/-8 and Sentinel-2) and radar (Sentinel-1, ENVISAT, ALOS/PALSAR, TerraSAR-X and RADARSAT) sensors. We also track thirty years of ice fronts with ASTER orthoimages and grounding line evolution with a double-difference SAR interferometry approach from a combination of ERS-½ and ESA Sentinel 1-a/b observations. We use the elevation time series to monitor the temporal evolution of the total ice shelf volume assuming hydrostatic equilibrium, and then combine them with the velocity time series to calculate basal melt rates in a Lagrangian framework. Finally, we compare our basal melt observations with CTD measurements of nearby ocean temperature and the TOPAZ4b reanalysis of Arctic ocean physics provided by Copernicus Marine Service.</div><div> </div><div>We show that significant changes for these last floating sectors of Greenland - some still undocumented - have occurred over the past 22 years. We analyze and discuss the relationship between recent ice shelf evolution and the loss of glacier mass draining through the ice shelves and the relationship with the evolution of deep ocean temperature and the evolution of the observed basal melt rate. We conclude with the possibility of current or future destabilization -or lack thereof- of glaciers in this area of Greenland.</div>