Evaporitic carbonates record surface melting in Antarctica

Abstract. Changes in Pleistocene Antarctic temperatures often coincide with variations in Northern Hemisphere summer insolation. While models invoking global CO₂ changes and shifts in oceanic and atmospheric circulation explain the temperature coherence between the poles, the role of Southern Hemisphere insolation in local Antarctic temperatures remain unclear. Here we present a temporal and geochemical record of Antarctic surface melting recorded by evaporitic carbonate formation from eight sites spanning the Amundsen Sea to the Ross Sea and 365m - 2000m in elevation. Isotopic data indicate water sourced from surface melt that weathers local rock and saturates carbonate through evaporation. U–Th dates restrict carbonate formation to three of the five most recent periods of high Southern Hemisphere summer insolation. These observations calibrate the effective albedo of darkened surfaces near nunataks and identify a Southern Hemisphere summer insolation threshold at which surface melt can occur under polar conditions.