Ocean-induced Melting of Greenland Ice Shelves

The Greenland glaciers have been experiencing ongoing acceleration and significant calving events during the last two decades. Ocean-induced melt is a potential trigger for destabilizing the glaciers and ice shelves, and consequently contributing to global sea level rise. However, its mechanism is still uncertain.In this dissertation, we employ observational and numerical methods to improve our under- standings of ocean-induced melt under major Greenland glaciers. Using improved remote sensing data, we calculate melt rates with an improved accuracy. We then employ the Mas- sachusetts Institute of Technology general circulation model (MITgcm) to study ice-ocean interactions beneath an ice shelf in a 2-D configuration at a high resolution. We include ther- mal forcing from the ocean, cavity shape, and for the first time subglacial water discharge at the grounding line. We optimize the heat and salt transfer coefficients to match observed results. The model replicates the general pattern of melting: high near the grounding zone, decreasing rapidly downstream. Melt increases below linear with subglacial discharge and above linear with thermal forcing from the ocean. Next, we investigate the role of the slope of the ice shelf draft in controlling ice shelf melt. The simulations indicate that the melt rate is sensitive to the slope, hence is larger for steeper ice shelves; and the location of the region of high melt migrates toward the grounding line as the slope becomes steeper. In the limit case of a vertical wall, no ice shelf, we know that the locus of ice melt undercuts the glacier.This study provides major new insights on the sensitivity of ice shelf melt to (1) subglacial water discharge: a direct product of ice sheet surface melt (2) thermal forcing from the ocean: a direct product of changes in ocean circulation as a result of wind forcing, and (3) a time-evolving cavity which affects the melt regimes: shallow, nearly flat cavities do not favor high melt; deep, steep cavities favor high melt. These results are important to interpret recent changes on the ice shelves and to inform ice sheet numerical models how to parameterize ice shelf melt in a changing climate