ABSTRACT: Fossil midges from Fog Lake, Baffin Island: long-term climate reconstruction in the Canadian Arctic and dynamics of species assemblages over a 90,000-year period.

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In order to answer questions concerning future global climate change, it is necessary to understand natural climate variation over a range of timescales in the past. The Canadian Arctic is an area particularly sensitive to climate change, and it is becoming critical to understand past climate change in the Arctic in detail. One proxy measure of temperature/climate that remains unexplored in arctic records is the fossil remains of the aquatic insect group Chironomidae (Diptera). Chironomid remains are being examined in a 137-cm core from Fog Lake on the Cumberland Peninsula, Baffin Island. The core was collected as part of the NSF-PALE initiative. Fog Lake probably remained unglaciated during the late Wisconsinan period. The core includes both Holocene sediments (Unit 5, gyttja), and pre-Holocene layers. Although sedimentation may not have been continuous in this lake, and dating of older strata remains problematic, it is believed that Units 1-4 represent a time period extending from the Holocene back to the penultimate glaciation. In addition to the Fog Lake core material, surface samples from a suite of lakes on a north-south transect of the Cumberland Peninsula were analyzed to provide additional data for chironomid-based temperature inference models developed for eastern Canada. Chironomid assemblages show dramatic shifts in species composition throughout the core, corresponding in part to the lithological units. Some taxa, such as Abiskomyia, are present only in the most recent intervals In Unit 4, a minerogenic laminated silt that probably represents OIS 2-4 during the last glacial maximum, Oliveridia is the dominant taxon, but is rare or absent in other sections of the core. Preliminary results indicate that water temperatures during this interval were around 10 C, although there may have been hiatuses in sediment accumulation during this period. The sediments in this unit may have been deposited during interstadials. Concentrations of head capsules were lowest in this time interval. In Unit 3, which was probably deposited during the last interglacial (OIS 5), inferred water temperatures are warmer than present. Warm conitions at this time were also suggested by the diatom and pollen data. Concentrations of head capsules were extremely high at the base of Unit 3, which is dated at approximately 90,000 yrs BP. Because assemblages are so distinctivE during Unit 4 (LGM), it does not appear that Fog L. was acting as a refugium for species that would colonize later, during the Holocene. This work represents one of the first stratigraphic studies of chironomid remains in Arctic Canada, and one of few anywhere to examine pre-Holocene assemblages.

Bibliography of Canadian Geomorphology