Glacier surface albedo from MODIS data and links to annual mass balance for the Gardens of Eden and Allah, New Zealand

Abstract

The Gardens of Eden and Allah (GoEA) are two of New Zealand’s largest icefields. However, their remote location and protected conservation status has resulted in a lack of in situ observations and measurements. As a result, the behaviour and dynamics of these unique glaciers are poorly understood. Long-term records of mass balance are required to understand the response of these glaciers to climate change. Recent studies have used the remotely sensed annual minimum glacier-wide albedo as a proxy for in situ glacier mass balance, thus avoiding the need for direct measurements. This research aims to characterise the variability of annual minimum glacier-wide albedo over the GoEA, and in-turn produce a long-term proxy record of glacier mass balance. To achieve this aim, records of annual minimum glacier-wide albedo are retrieved from near-daily satellite imagery captured since February 2000 by Terra’s MODerate-resolution Imaging Spectroradiometer (MODIS). For this analysis, 12 outlet glaciers are identified in the GoEA, using a new and objective approach to determining glacier boundaries. To investigate the variability of annual minimum glacier-wide albedo yr and its link to mass balance across the GoEA, a 17-year time-series of near-daily glacier surface albedo is produced for each outlet glacier (2000–2017).

Between 2000 and 2017, the outlet glaciers demonstrate significant variability in the timing and magnitude of annual minimum glacier-wide albedo, which is influenced in-part by glacier aspect and topography. In spite of the variability between glaciers; a coherent record of behaviour is produced from the average annual minimum glacier-wide albedo across the outlet glaciers since 2000. Positive and negative shifts in the average annual minimum glacier-wide albedo of the GoEA broadly reflect in situ and proxy mass balance records from other glaciers in the Southern Alps during the same period. These results suggest that the GoEA follow the broad response of glaciers in the Southern Alps to climate. The reconstruction of these long-term albedo records from previously unmonitored glaciers will continue to inform on the spatial variability in glacier response to climatic change. These results demonstrate the value of MODIS for monitoring large, remote glaciers, and in doing so, will allow for better management of New Zealand’s important cryospheric resources.