Description: 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 (d18O 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 d18O diatom record from an 82 cm sediment core (Ni-2B). The well-mixed lake (d18O water = -17.4‰) is influenced by a heavier (less negative) isotope composition (-18.80‰) from Amadjuak River draining Amadjuak Lake to the South and water of lighter (more negative) isotopic composition (-16.4‰) from the Isurtuq River originating from Penny Ice Cap in the North-East. From the d18O water and d18O diatom of the topmost sample of core Ni-2B a D18O silica-water of 1000 ln alpha(silica-water) = 40.2‰ 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 d18O diatom variations in the core of more than 13‰ are mainly induced by changes in the isotopic composition of the lake water due to a shift from glaciomarine (d18O diatom = +34.6‰) through brackish (+23.4 to +27.2‰) towards lacustrine (+21.5‰) 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 d18O diatom. Additionally, for the lacustrine section it could be demonstrated that d18O diatom may serve as a proxy for past air temperature within the same core recording a late Holocene cooling of about 4°C being consistent with other published values for the greater Baffin region.

Description: The need for better understanding of long-term climate and environmental variability in the Foxe Basin (Nunavut, Canada) is highlighted by the major environmental changes in this highly sensitive region, which occupies a transitional position between areas undergoing drastic and more subtle changes in the High and Low Canadian Arctic over the course of the last millennium, respectively. However, high-resolution long-term climate records remain scarce in the Foxe Basin region even though it is of key importance to understanding Holocene climate evolution since the last deglaciation. In order to reconstruct the regional postglacial climatic and environmental variability, we adopted a multi-proxy paleolimnological approach analysing sedimentary records retrieved from Nettilling Lake on southern Baffin Island, involving elemental geochemistry from high-resolution µ-XRF analyses, diatom assemblage composition and oxygen isotope records from fossil diatom silica (δ18Odiatom). The oxygen isotope composition of diatoms (δ18Odiatom) yields extremely large δ18Odiatom variations in the core of more than 13‰ which are mainly driven by changes in the isotopic composition of the lake water due to a shift from glacio-marine to brackish (at ca. 7400 yr cal BP) towards lacustrine conditions (at ca. 6000 yr cal BP) associated with decreasing salinity also documented by shifts in the composition of diatom assemblages. Our study provides evidence that paleo-salinity can be inferred from δ18Odiatom. Additionally, in the lacustrine section of the core,, δ18Odiatom may also serve as a proxy for past air temperatures recording a late Holocene cooling of about 4°C for the greater Baffin region. Furthermore, the results obtained from our study provide new insights into the timing of regional glacier retreat (ca. 8300 cal BP) and the duration of the postglacial marine invasion (from ca. 7400 cal BP to ca. 6000 cal. BP), thereby complementing ongoing research of postglacial environmental dynamics in the Foxe Basin and on south-western Baffin Island.

Description: Thermokarst lakes are widespread in arctic and subarctic regions. In subarctic Québec (Nunavik), they have grown in number and size since the mid-20th century. Recent studies have identified that these lakes are important sources of greenhouse gases. This is mainly due to the supply of catchment-derived dissolved organic carbon that generates anoxic conditions leading to methane production. To assess the potential role of climate-driven changes in hydrological processes to influence greenhouse-gas emissions, we utilized water isotope tracers to characterize the water balance of thermokarst lakes in Nunavik during three consecutive mid- to late summer seasons (2012-2014). Lake distribution stretches from shrub-tundra overlying discontinuous permafrost in the north to spruce-lichen woodland with sporadic permafrost in the south. Calculation of lake-specific input water isotope compositions (I) and lake-specific evaporation-to-inflow (E/I) ratios based on an isotope-mass balance model reveal a narrow hydrological gradient regardless of diversity in regional landscape characteristics. Nearly all lakes sampled were predominantly fed by rainfall and/or permafrost meltwater, which suppressed the effects of evaporative loss. Only a few lakes in one of the southern sampling locations, which overly highly degraded sporadic permafrost terrain, appear to be susceptible to evaporative lake-level drawdown. We attribute this lake hydrological resiliency to the strong maritime climate in coastal regions of Nunavik. Predicted climate-driven increases in precipitation and permafrost degradation will likely contribute to persistence and expansion of thermokarst lakes throughout the region. If coupled with an increase in terrestrial carbon inputs to thermokarst lakes from surface runoff, conditions favorable for mineralization and emission of methane, these water bodies may become even more important sources of greenhouse gases.

Description: The need for better understanding of long-term climate and environmental variability in the Foxe Basin (Nunavut, Canada) is highlighted by the major environmental changes in this highly sensitive region, which occupies a transitional position between areas undergoing drastic and more subtle changes in the High and Low Canadian Arctic over the course of the last millennium, respectively. However, high-resolution long-term climate records remain scarce in the Foxe Basin region even though it is of key importance to understanding Holocene climate evolution since the last deglaciation. In order to reconstruct the regional postglacial climatic and environmental variability, we adopted a multi-proxy paleolimnological approach analysing sedimentary records retrieved from Nettilling Lake on southern Baffin Island, involving elemental geochemistry from high-resolution µ-XRF analyses, diatom assemblage composition and oxygen isotope records from fossil diatom silica (δ18Odiatom). The oxygen isotope composition of diatoms (δ18Odiatom) yields extremely large δ18Odiatom variations in the core of more than 13‰ which are mainly driven by changes in the isotopic composition of the lake water due to a shift from glacio-marine to brackish (at ca. 7400 yr cal BP) towards lacustrine conditions (at ca. 6000 yr cal BP) associated with decreasing salinity also documented by shifts in the composition of diatom assemblages. Our study provides evidence that paleo-salinity can be inferred from δ18Odiatom. Additionally, in the lacustrine section of the core,, δ18Odiatom may also serve as a proxy for past air temperatures recording a late Holocene cooling of about 4°C for the greater Baffin region. Furthermore, the results obtained from our study provide new insights into the timing of regional glacier retreat (ca. 8300 cal BP) and the duration of the postglacial marine invasion (from ca. 7400 cal BP to ca. 6000 cal. BP), thereby complementing ongoing research of postglacial environmental dynamics in the Foxe Basin and on south-western Baffin Island.

Description: Nettilling Lake (Baffin Island, Nunavut) is currently the largest lake in the Canadian Arctic Archipelago. Despite its enormous size, this freshwater system remains little studied until the present-day. Existing records from southern Baffin Island indicate that in the early postglacial period, the region was submerged by the postglacial Tyrell Sea due to isostatic depression previously exerted by the Laurentide Ice Sheet. However, these records are temporally and spatially discontinuous, relying on qualitative extrapolation. This paper presents the first quantitative reconstruction of the postglacial environmental succession of the Nettilling Lake basin based on a 8300 yr-long high resolution sedimentary record. Our multi-proxy investigation of the glacio-isostatic uplift and subsequent changes in paleosalinity and sediment sources is based on analyses of sediment fabric, elemental geochemistry (m-XRF), diatom assemblage composition, as well as on the first diatom-based oxygen isotope record from the eastern Canadian Arctic. Results indicate that the Nettilling Lake basin experienced a relatively rapid and uniform marine invasion in the early Holocene, followed by progressive freshening until about 6000 yr BP when limnological conditions similar to those of today were established. Our findings present evidence for deglacial processes in the Foxe Basin that were initiated at least 400yrs earlier than previously thought.