Remote Sensing of Icebergs in Greenland\u27s Fjords and Coastal Waters

Increases in ocean water temperature are implicated in driving recent accelerated rates of mass loss from the Greenland Ice Sheet. Icebergs provide a key tool for gaining insight into ice-ocean interactions and until recently have been relatively understudied. Here we develop several methods that exploit icebergs visible in optical satellite imagery to provide insight on the ice--ocean environment and explore how iceberg datasets can be used to examine the physics of iceberg decay and parent glacier properties. First, a semi-automated algorithm, which includes a machine learning-based cloud mask, is applied to six years (2000-2002 and 2013-2015) of the Landsat archive to derive iceberg size distributions for Disko Bay. These data show an increase in the total number of icebergs and suggest a change in the shape of the iceberg size distribution, concurrent with a shift in the dominant calving style of Sermeq Kujalleq (Jakobshavn Isbrae), their parent glacier. Second, bathymetry is qualitatively and quantitatively inferred using icebergs as drifters; regions of iceberg drifting and stranding indicate relative bathymetric lows and highs, respectively. To quantify water depth in shallow regions, iceberg draft is inferred from iceberg freeboard under the assumption of hydrostatic equilibrium where very high-resolution stereo image pairs of icebergs are available to construct digital elevation models. Although this results in water depths with relatively large uncertainties, the method provides valuable quantitative data in regions where bathymetric observations are unavailable, improving our understanding of sill locations and the consequent ability of warm ocean waters to reach glacier termini. Third, we use the iceberg datasets derived using the previously described methods to probe the spatial patterns of iceberg size distributions. Rigorous discrimination between power law and lognormal size distributions is challenging, but our datasets corroborate the idea that as icebergs move farther from the parent glacier and the primary control on iceberg size transitions from fracture to melting, their size distribution shifts from power law to lognormal. Overall, our analysis suggests that future thorough investigations of iceberg size distributions will serve as a valuable tool to gain insights into the physics of iceberg decay and properties of the parent glacier