Spatial analysis of cirques from three regions of Iceland: implications for cirque formation and palaeoclimate

摘要

> This study is a quantitative analysis of cirques in three regions of Iceland: Tr?llaskagi, the East Fjords and Vestfireir. Using Google Earth and the National Land Survey of Iceland Map Viewer, we identified 347 new cirques on Tr?llaskagi and the East Fjords region, and combined these data with 100 cirques previously identified on Vestfireir. We used Arc GIS to measure length, width, aspect, latitude and distance to coastline of each cirque. Palaeo‐equilibrium‐line altitudes (palaeo‐ ELA s) of palaeo‐cirque glaciers were calculated using the altitude‐ratio method, cirque‐floor method and minimum‐point method. The mean palaeo‐ ELA values in Tr?llaskagi, the East Fjords and Vestfireir are 788, 643 and 408?m a.s.l, respectively. Interpolation maps of palaeo‐ ELA s demonstrate a positive relationship between palaeo‐ ELA and distance to coastline. A positive relationship between palaeo‐ ELA and latitude is observed on Vestfireir, a negative relationship is observed on Tr?llaskagi and no statistically significant relationship is present on the East Fjords. The modal orientation of cirques on Tr?llaskagi and Vestfireir is northeast, while orientation of cirques in the East Fjords is north. Palaeo‐wind reconstructions for the LGM show that modal aspect is?aligned with the prevailing north‐northeast wind directions, although aspect measurements demonstrate wide dispersion. Cirque length is similar on Tr?llaskagi and the East Fjords, but cirques are approximately 200?m shorter in Vestfireir. Cirque widths are similar in all three regions. Comparisons with a global data set show that cirques in Iceland are smaller and more circular than cirques in other regions of the world. Similar to glaciers in Norway and Kamchatka, our results demonstrate that access to a moisture source is a key parameter in determining palaeo‐ ELA s in Iceland. Temperatures interpreted from palaeo‐ ELA depressions suggest that these cirques may have been glaciated as recently as the Little Ice Age.