Holocene warmth explains the Little Ice Age advance of Sermeq Kujalleq

Our understanding of the processes driving the sea-level contribution of fast-flowing marine-terminating glaciers of the Greenland ice sheet is largely based on observations from the 20th century, with a large bias towards retreating glaciers. The pre-industrial extent of the ice edge is preconditioned by the long and warm Holocene period (from 9700 BCE), followed by a cooling culminating in the Little Ice Age (1250–1900 CE). To improve our understanding of ice dynamics, the evolution of rapidly flowing outlet glaciers should be reviewed in the context of centennial to millennial scale climate variability. Using proxy records and a numerical ice sheet model, we reconstruct the advance of Sermeq Kujalleq (Jakobshavn Isbrae) during the Little Ice Age. We find that the recorded extent of the advance requires an upstream source of soft and deformable ice, combined with reduced calving at the front. We highlight that the Little Ice Age marks the maximum extent of the glacier, following a longer, centennial, period of advance. The subsequent retreat of the glacier front from the Little Ice Age overlaps with the current period of Anthropogenic climate warming, making it difficult to disentangle the Anthropogenic contribution to the 20th century retreat.