In Situ Measurements and Modeling Used to Constrain Heat Transfer in the Western Greenland Ice Sheet

• Main Author: Hills, Benjamin H
• Format: Other/Unknown Material
• Language: unknown
• Published: University of Montana 2017
• Subjects: Ice; Heat Transfer; Greenland; Ablation Zone; Diffusion; Latent Heat; Glaciology; Ice Sheet
• Online Access: https://scholarworks.umt.edu/etd/10940; https://scholarworks.umt.edu/context/etd/article/11991/viewcontent/Hills_Benjamin_Thesis.pdf

The temperature of ice in the Greenland Ice Sheet results from the interaction of multiple heat sources and heat transfer mechanisms. We present a large set of in situ ice temperature measurements within the ablation zone of southwest Greenland, including twenty boreholes to the bed at six sites and seven shallow boreholes to 20 m depth at three of those sites. We use these measurements with modeling to establish constraints on the sourcing of heat and its transfer over a range of length scales. First, we examine the ice temperature conditions along the surface boundary of the ice sheet. We compare the measured ice temperature below a maximum depth of seasonal variations to the measured air temperature. We identify five processes that may cause the ice temperature to differ from the mean annual air temperature. Near-surface temperature and meteorological data are input to a simple modeling case study to assess the relative importance of each of the five processes on near-surface heat transfer and the impacts on near surface ice temperature. Second, we investigate ice temperature across the full ice depth. We find that, overlain on a longitudinal warming gradient which extends across the ablation zone, there are horizontal gradients in ice temperature over three distinct length scales. Simple modeling results imply that variations in vertical ice advection lead to the development of horizontal gradients on the scale of an ice thickness. In addition, latent heating causes the evolution of horizontal gradients at two scales: 1) at the regional scale (km's), probably associated with large crevasse fields, and 2) at a highly confined and localized scale (hundreds of meters), likely associated with isolated crevasse or moulin features. This work shows that the thermal structure of Greenland's ablation zone is more complex than previously thought, with horizontal temperature gradients resulting in heat flow in all directions and across a range of length scales.