THE “CRYSTAL EYE OF NUNAVIK” (PINGUALUIT CRATER LAKE): DIATOM INFERRED PALEOENVIRONMENTAL RECORD FOR THREE PREVIOUS INTERGLACIAL PERIODS

Most lakes in the northern circumpolar region are of glacial origin and allow reconstructions that date back only until the last deglaciation several thousand years ago, due to glacial erosion of their sediment infill. With the exception of the El'gygytgyn Crater Lake in Siberia, all other climate archives of the Arctic covering several interglacials originate from marine sediments or ice cores. The sediments of the 1.4. Ma old Pingualuit Crater Lake (Nunavik, Canada; 61°17'N, 73°41'W) - known as the “Crystal Eye of Nunavik”- offer the unique opportunity to study terrestrial climate dynamics not only during the postglacial period, but potentially over several hundreds of thousands of years as its deep sediment infill promises to yield an uninterrupted arctic paleoclimate record covering several interglacial-glacial cycles. Previous attempts to core the lake have resulted in the collection of only 14 cm of sediments that spanned the last ~5000 years. In May, 2007 ~10 m of sediments was recovered from the crater lake at a water depth of 270 m using a UWITEC piston percussion corer system. Here we will present initial results of limnological measurements (PAR, UV light transparency) performed on the water column of one of the deepest and most transparent lakes on this planet, as well as preliminary sedimentological, micropaleontological and stratigraphic interpretations. The initial results revealed the presence of at least two decimetre-thick intervals composed of laminated, dark grey clayey silts characterized by a relatively low density and magnetic susceptibility, that contrast sharply with the thicker over- and underlying sections with light grey, denser, sandy sediments. Moreover, these two intervals revealed the presence of fossil diatoms and chrysophytes, suggesting that these two intervals represent ice-free conditions and thus likely interglacials, whereas the more extensive light grey and sandy sediments probably reflect glacial intervals. This interpretation will be tested by ongoing paleomagnetic (i.e., magnetostratigraphy) and multi-proxy biostratigraphic analyses (diatoms, chironomids, cladocerans, pollen), as well as radiocarbon and thermoluminescence (TL) dating. A first TL estimation in the uppermost laminated (interglacial) interval suggests it is MIS 5d.