Title

Firn Densification in the Percolation Zone of Western Greenland

Presentation Type

Poster

Abstract

The contribution to sea level rise by the Greenland Ice Sheet (GrIS) is controlled by surface mass balance (accumulation and ablation) and dynamical discharge. Ablation and dynamical discharge can increase sea level by introducing this mass into the oceans as fresh water. In the accumulation zone of a glacier, where annual snowfall exceeds melt, the densification of snow that has survived a melt season (firn), contributes to surface elevation changes without loss of mass. This complicates mass balance assessment since a change in surface elevation doesn’t directly translate to a change in mass for the ice sheet. The densification process is well understood for “dry snow zones” where seasonal surface melt is absent; however, lower in the accumulation zone, densification processes are complicated by seasonal melt water which penetrates down into the firn and refreezes. Refreezing melt water can enhance densification by redistributing mass and by releasing heat when transitioning from a liquid to a frozen state. This study (a work in progress) addresses what depths these occur and how much heat is generated through the analysis of firn temperature data collected from ten sites along a 90 km transect through the percolation zone of western Greenland. Comparing a partial differential equation that describes how temperature diffuses in the absence of refreezing with temperature data that includes these events, a residual heat value which represents the total amount of heat that results from at least three distinct types of refreezing events is calculated. One of these types of refreezing events is addressed using measured temperature data to find anomalies unique to this event type. The likelihood for refreezing in specific depth ranges below the surface is represented by a probability density function that will later be used to constrain a firn densification model.

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Apr 12th, 3:00 PM Apr 12th, 4:00 PM

Firn Densification in the Percolation Zone of Western Greenland

UC Ballroom

The contribution to sea level rise by the Greenland Ice Sheet (GrIS) is controlled by surface mass balance (accumulation and ablation) and dynamical discharge. Ablation and dynamical discharge can increase sea level by introducing this mass into the oceans as fresh water. In the accumulation zone of a glacier, where annual snowfall exceeds melt, the densification of snow that has survived a melt season (firn), contributes to surface elevation changes without loss of mass. This complicates mass balance assessment since a change in surface elevation doesn’t directly translate to a change in mass for the ice sheet. The densification process is well understood for “dry snow zones” where seasonal surface melt is absent; however, lower in the accumulation zone, densification processes are complicated by seasonal melt water which penetrates down into the firn and refreezes. Refreezing melt water can enhance densification by redistributing mass and by releasing heat when transitioning from a liquid to a frozen state. This study (a work in progress) addresses what depths these occur and how much heat is generated through the analysis of firn temperature data collected from ten sites along a 90 km transect through the percolation zone of western Greenland. Comparing a partial differential equation that describes how temperature diffuses in the absence of refreezing with temperature data that includes these events, a residual heat value which represents the total amount of heat that results from at least three distinct types of refreezing events is calculated. One of these types of refreezing events is addressed using measured temperature data to find anomalies unique to this event type. The likelihood for refreezing in specific depth ranges below the surface is represented by a probability density function that will later be used to constrain a firn densification model.