Holocene-like summer climate during Marine Isotope Stage 11 in northwestern Greenland

Determining the climatic conditions under which the Greenland Ice Sheet (GrIS) was smaller than present is important to quantify GrIS sensitivity to climate change. We use biomarkers in sediment collected beneath the GrIS at Camp Century, northwestern Greenland, to reconstruct summer temperature and atmospheric circulation 416 000 ± 38 000 years ago, at some point during Marine Isotope Stage 11 (MIS 11). We find that northwestern Greenland summer climate during MIS 11 was similar to the middle Holocene but different than the 20th century. Air temperature was 4.7 ± 3.2 °C warmer, and atmospheric water vapor isotope values were 22 ± 18 ‰ 2 H-enriched, indicating a greater contribution of locally evapotranspired moisture. These conditions are similar to or slightly warmer than during peak Holocene warmth on Greenland, when the Camp Century site remained ice-covered, and cooler than the Last Interglacial (LIG). Biomarkers from lower in the section likely represent an earlier ice-free interval, potentially during the Pliocene or early Pleistocene, and record climatic conditions similar to MIS 11. These data add to the sparse available climate data for the early and middle Pleistocene on Greenland, and suggest interglacial periods had similar temperature throughout the Pleistocene. We interpret the reduced GrIS extent in northwestern Greenland during MIS11 compared to the Holocene, despite similar temperature, to indicate ice-sheet response to prolonged warmth, as reconstructed in southern Greenland. Therefore, efforts to reduce both the magnitude and duration of summer warmth in the coming centuries will be important to curbing ice-sheet retreat.