Paleo-environmental gateways in the eastern Canadian arctic - Recent isotope hydrology and diatom oxygen isotopes from Nettilling Lake, Baffin Island, Canada

[摘要] Nettilling Lake is located on Baffin Island, Nunavut, Canada between the areas of past warming (Canadian High Arctic to the North) and climatic stability (Northern Quebec and Labrador region to the South). Despite being the largest lake in the Nunavut region with a postglacial marine to lacustrine transition history only a few paleo-environmental investigations were completed in this area. The oxygen isotope composition of diatoms (delta O-18(diatom)) can provide valuable insights into paleo-environmental conditions. Here, the recent (isotope) hydrology and hydrochemical data from the lake are presented to facilitate the interpretation of a delta O-18(diatom) record from an 82 cm sediment core (Ni-2B). The well-mixed lake (delta O-18(water) = 17.4 parts per thousand) is influenced by a heavier (less negative) isotope composition (-18.80 parts per thousand) from Amadjuak River draining Aniadjuak Lake to the South and water of lighter (more negative) isotopic composition (-16.4 parts per thousand) from the Isurtuq River originating from Penny Ice Cap in the North-East. From the delta O-18(water) and delta O-18(diatom) of the topmost sample of core Ni-2B a Delta O-18(silica-water) of 1000 In alpha((silica-water)) = 40.2 parts per thousand for sub -recent diatoms of Nettilling Lake was calculated matching the known water -silica fractionation for fossil sediments well and thereby showing the general applicability of this proxy for paleo-reconstructions in this region. Extremely large delta O-18(diatom) variations in the core of more than 13 parts per thousand are mainly induced by changes in the isotopic composition of the lake water due to a shift from glaciomarine (delta O-18(diatom) = +34.6 parts per thousand) through brackish (+23.4 to +27.2 parts per thousand) towards lacustrine (+21.5 parts per thousand) conditions (transition zones glaciomarine to brackish at 69 cm/7300 yr cal. BP and brackish to lacustrine at 35 cm/6000 yr cal. BP) associated with a shift in the degree of salinity. Our study provides the first evidence that paleo-salinity can be reconstructed by delta O-18(diatom). Additionally, for the lacustrine section it could be demonstrated that delta O-18(diatom) may serve as a proxy for past air temperature within the same core recording a late Holocene cooling of about 4 degrees C being consistent with other published values for the greater Baffin region. (C) 2016 Elsevier Ltd. All rights reserved.

[发布日期] 2016-09-01

[效力级别]  Proceedings Paper

[关键词] Biogenic silica;Climate-reconstruction;Arctic;Post-glacial;Marine-lacustrine transition