Cladocerans and diatoms from an Early Pleistocene interglacial deposit at Pingorsuit, North-West Greenland

At the margin of the Pingorsuit Glacier in North-West Greenland, an organic-rich deposit that has recently emerged from the retreating ice cap was discovered in 2019 at an elevation of 480 m above sea level. Here we report on cladoceran and diatom analyses of this freshwater deposit from three samples of detritus gyttja, which occurred beneath a thin cover of till and glaciofluvial deposits. The cladoceran fauna comprises many non-Greenlandic, non-Arctic taxa, in accordance with previous studies of Coleoptera, Trichoptera and vascular plants. The fossil assemblages from the Pingorsuit beds resemble other fossil assemblages from Greenland that have been assigned an Early Pleistocene age, and a similar age has been suggested for the sediments found at the margin of the Pingorsuit Glacier. The fossil cladoceran and diatom species indicate a shallow lake with oligo- and dystrophic, circumneutral to slightly acidic waters. Their assemblages are more diverse compared to Holocene assemblages from northern Greenland, further indicating warmer summers than present.