Heightened sensitivity of a poorly buffered high arctic lake to late-Holocene climatic change (original) (raw)
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Écoscience, 2021
ABSTRACT The Arctic has warmed significantly over the past decades. However, the evolution of Arctic climate during the Holocene remains to be clarified in more detail, and regional factors controlling aquatic ecosystem evolution need to be better defined to grasp the sensitivity of lakes to rapid environmental change. Nettilling Lake was studied for changes in sedimentary diatom assemblages over the last 5 000 years. Lake water pH was reconstructed by applying a diatom-based lake water pH inference model. We hypothesized that the changes in diatom assemblages were driven by variations in lake water transparency and attendant water turbidity associated with the input of fine suspended solids from glacial meltwaters. Reduced underwater light resulted in greater abundance of planktonic over benthic taxa from ca. 5 000 to 3 000 yrs. cal. BP, followed by less turbid conditions and proliferation of benthic taxa during regional cooling. The lake water was slightly alkaline throughout the Holocene, ranging between pH 7.1 and 7.7. Our results support the notion that hydrological processes, dependent on climate variations, have a first-order influence on the regulation of the lake water pH through glacial meltwater inputs, which will likely continue to control the lake's long-term chemical and biological evolution.
2002
A fossil diatom record covering the past 3000 cal. years BP was analyzed from a small lake in northwesterń Quebec near the northern limit of present-day tree-line. Fragilaria virescens var. exigua Grunow in Van Heurck was the dominant species throughout the core with abundances ranging between 13-35% of the total valve count. There was a replacement of alkaliphilous taxa by acidophilous taxa beginning ca. 1300 cal. yr ago, probably reflecting long-term, natural acidification processes. A diatom-based transfer function was used to provide quantitative estimates of variations in lakewater dissolved organic carbon (DOC). These inferred values showed 21 that DOC concentrations have remained stable over the past 3000 years (mean 6 S.D. 5 5 6 0.43 mg C l ), suggesting relatively constant allochthonous carbon inputs and underwater light conditions during the late Holocene. The reconstructed DOC data were compared to the palynological record from the same lake. Our study indicates that, in contrast to paleolimnological records from lakes in central and western Canada, climatic variations and associated vegetational shifts have been too subtle to cause pronounced variations in DOC in thiś northern Quebec site.
2016
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 i...
2016
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 i...
Journal of Quaternary Science, 2014
Inference models from diatoms preserved in lake sediments can be used to reconstruct long-term pH changes to better understand the process of lake ontogeny. An expanded diatom training set was developed using taxonomically harmonized modern assemblages in surface sediments of 171 lakes spanning a variety of geological and climatic settings across the Canadian Arctic. Lake-water pH emerged as a significant variable and the most influential in structuring diatom assemblages. The resulting two-component weighted-averaging partial least squares pH inference model performs strongly, even after identifying effects of spatial autocorrelation at distances <20 km. The model was then applied to three dated Holocene diatom stratigraphies from Arctic regions of contrasting bedrock geology and buffering capacity, and the significance of the pH reconstructions was assessed. At Lake CF3 in a poorly buffered catchment, a gradual but significant pH decline begins 5000 years after lake inception, coincident with regional Late Holocene cooling. Reconstructions for two well-buffered, more alkaline sites were not significant, probably due to poor analogues and other factors driving changes in diatom assemblages. Due to sparse soil and vegetation in these and other Arctic basins, bedrock composition is the most important regulator of Holocene pH, and only in poorly buffered lakes does pH primarily represent a climate signal.
The Holocene, 2021
The paleolimnological record of diatoms and climate, spanning the last 2800 years, was investigated in a small subarctic lake (Pocket Lake) that from AD 1948 to 2004 was contaminated by gold smelting waste. An age-depth model was constructed using a combination of 210Pb, 14C, and tephra to determine a 2800 year history of lake ontogeny (natural aging), biological diversity, and regional climate variability. Diatoms form six strong paleoecological assemblages over time in response to changes in local hydrological and sedimentological conditions (including metals). Selected environmental variables explained 28.8% of the variance in the diatom assemblages, with Fe, Ca, and sediment end member distribution being important indicators. The diatom assemblages correlated to the Iron Age Cold Epoch (2800–2300 cal BP), Roman Warm Period (2250–1610 cal BP), Dark Age Cold Period (1500–1050 cal BP), Medieval Climate Anomaly (ca. 1100–800 cal BP), and the Little Ice Age (800–200 cal BP). The disa...
Journal of Quaternary Science, 2021
Sedimentary diatoms have been used to quantitatively reconstruct climate-related variables, such as temperature at different timescales. Even though temperature is often less of a key driver of diatom ecology than other environmental parameters (water chemistry), diatom inference models have been shown to be reliable in deducing past temperature trends. In addition, the oxygen isotope composition (δ 18 O diatom) preserved in buried diatom frustules has demonstrated its potential to reflect climatic and hydrological conditions at the time of frustule formation. This study combines results from both diatom-based climate proxies to reconstruct summer water and mean annual air temperatures, and hydrological trends in Nettilling Lake, Baffin Island, from ca. 5000 to 500 cal a BP. Diatom-inferred temperatures revealed an overall ca. 2°C cooling throughout the Late-Holocene. The δ 18 O diatom values showed an increasing trend up to ca. 1900 cal a BP, where they reached their highest values (+24.8‰ at 15 cm) and thereafter decreased to their lowest values (+21.4‰ at 4 cm). These trends were linked to meltwater inflows associated with Penny Ice Cap thaw rate that was in turn controlled by regional climatic conditions which went from intensified cooling during the Neoglacial period to slight warming thereafter. Our results suggest that diatom-and diatom-isotope-based temperature and hydrological reconstructions can identify trends related to the natural climate system variability. The diatom oxygen isotopes are useful for paleoenvironmental studies of terrestrial aquatic ecosystems, but not for all hydrological systems are the ideal temperature proxy. Hence, the combination of proxies helps to disentangle temperature and hydrological effects for paleoclimatic reconstructions and may support future studies of postglacial environmental change in northern lakes.
Quaternary Science Reviews
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 (d 18 O 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 d 18 O diatom record from an 82 cm sediment core (Ni-2B). The well-mixed lake (d 18 O water ¼ À17.4‰) is influenced by a heavier (less negative) isotope composition (À18.80‰) from Amadjuak River draining Amadjuak Lake to the South and water of lighter (more negative) isotopic composition (À16.4‰) from the Isurtuq River originating from Penny Ice Cap in the NorthEast. From the d 18 O water and d 18 O diatom of the topmost sample of core Ni-2B a D 18 O silica-water of 1000 ln a (silica-water) ¼ 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 d 18 O 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 (d 18 O diatom ¼ þ34.6‰) through brackish (þ23.4 to þ27.2‰) towards lacustrine (þ21.5‰) 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 d 18 O diatom. Additionally, for the lacustrine section it could be demonstrated that d 18 O 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.
Diatom response to mid-Holocene climate in three small Arctic lakes in northernmost Finnmark
The Holocene
Palaeoclimatic reconstructions from lake sediment biological records can be challenging, due to variation in non-climatic factors, which alter ecosystem responses. To consider this, it is important to replicate a study regionally, so as to gain information on spatial variability of ecosystem response and the influence of site-specific conditions. Previous pollen-based palaeoclimatic records from three well-dated Arctic lake sites highlight the response of regional Scots Pine ( Pinus sylvestris) and Mountain Birch ( Betula pubescens ssp. czerepanovii) forest-tundra transition to Holocene climatic variability and suggest the northernmost Peninsulas of Finnmark to be climatically sensitive. This study analysed dated sediment sequences between c. 3970 and c. 6200 cal. yr BP from these three previously published shallow lakes: Liten Čap’pesjav’ri (LCJ), over Gunnarsfjorden (OGF) and over Kobbkrokvatnet (OKV), for freshwater diatoms. Diatom assemblages showed an increase in the planktonic...