Climatic implications of reconstructed early-mid Pliocene equilibrium-line altitudes in the McMurdo Dry Valleys, Antarctica

Early mid Pliocene moraines in the McMurdo Dry Valleys, Antarctica, are more extensive than the present alpine glaciers in this region, indicating substantial climatic differences between the early mid Pliocene and the present. To quantify this difference in the glacier climate regime, we estimated the equilibrium-line altitude (ELA) change since the early mid Pliocene by calculating the modern ELA and reconstructing the ELAs of four alpine glaciers in Wright and Taylor Valleys at their early mid Pliocene maxima. The area altitude balance ratio method was used on modern and reconstructed early mid Pliocene hypsometry. In Wright and Victoria Valleys, mass-balance data identify present-day ELAs of 800-1600m a.s.l. and an average balance ratio of 1.1. The estimated ELAs of the much larger early mid Pliocene glaciers in Wright and Taylor Valleys range from 600 to 950 +/- 170 m a.s.l., and thus are 250-600 +/- 170 m lower than modern ELAs in these valleys. The depressed ELAs during the early-mid-Pliocene most likely indicate a wetter and therefore warmer climate in the Dry Valleys during this period than previous studies have recognized.