Pro- and postglacial invertebrate communities of Pingualuit Crater Lake, Nunavik (Canada), and their paleoenvironmental implications

Abstract

Zoological remains were examined from the sediments of the Pingualuit Crater Lake, Nunavik, Canada. Our objective was to describe past climate events in the area of delayed deglaciation in northernmost Ungava Peninsula. Our record covers 3 separate sections of deglacial and postglacial invertebrate dynamics interrupted by laminated proglacial sediments and a basin-scale erosive slumping event. The abundance of animal remains in the ultra-oligotrophic and extremely deep arctic lake was low, but distinct faunal assemblages were found among the intervals, results implying that they were environmentally heterogeneous. The lowermost fine-grained interval (before 6850 calibrated years before present [cal BP]), revealed that Cladocera Chydorus sphaericus-type and Bosmina (Eubosmina) longispina-type were common in the lake, whereas Chironomidae were relatively rare. The dominance of B. longispina-type showed that planktonic communities were successful at the time, probably indicating more favorable climatic conditions than today soon after the last deglaciation (∼7000 cal BP). In the middle interval (between ∼6850 and 5750 cal BP), chironomids became more common and were dominated by Heterotrissocladius subpilosus-type and Protanypus, taxa that are characteristic of oligotrophic lakes. The extirpation of B. longispina-type suggests that planktonic invertebrate communities were not successful, probably because of predation by Arctic char. The presence of the chironomid Oliveridia tricornis-type during the late Holocene (between ∼4200 and 600 cal BP) suggested general climate cooling. Our paleoclimatic conclusions on the regional environmental history suggest a stationary ice front in the initial stages of the Holocene, favorable climatic conditions in the mid-Holocene and a general late-Holocene cooling. Our records also indicate a subtle increase in nutrient availability throughout the Holocene. The paleoecological record from Pingualuit Crater Lake is valuable in describing the faunal history and biotic resilience in this environmentally extreme lake, which presently contains one of the world’s softest and most transparent waters.