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Sediment cores from 13 lakes in a 1500 km transect along the eastern North American Arctic contain up to four superposed stratified interglacial units. All 13 lakes contain one unit with sediment similar in character and mass to Holocene gyttja, with 14C ages >40 ka, luminescence ages 90 to 120 ka, and pollen assemblages that require nearly complete Laurentide deglaciation, supporting a Last Interglacial (LIG; MIS 5e) age. Two lakes preserve an older interglacial, with luminescence ages suggesting an MIS 7 age. Four adjacent lakes record a thin, stratified organic unit between the LIG and Holocene units with 14C ages >50 ka, that is probably from late in MIS 5. Temperature estimates from biotic proxies suggest LIG summer temperatures 4–6°C above mid‐20th century values; pollen, chironomids and DNA document a poleward expansion of woody plants and invertebrate species during the LIG, supporting arguments that positive feedbacks native to the Arctic amplified insolation‐driven summer temperature increases. The stratigraphic succession implies the Laurentide Ice Sheet remained intact with sea level below ‐40 m from ~115 ka to ~11 ka, and places new constraints on the interpretation of cosmogenic radionuclide inventories in erratic boulders older than the Holocene throughout this region. [ABSTRACT FROM AUTHOR]

Although recent ecological changes are widespread in Arctic lakes, it remains unclear whether they are more strongly associated with climate warming or the deposition of reactive nitrogen (Nr) from anthropogenic sources. We developed a 3500-yr paleolimnological record from the world's northernmost lake to explore this question. Microfossils indicate that siliceous diatoms and chrysophytes were abundant initially, but disappeared 2400 yr ago in concert with Neoglacial cooling. Microfossils reappear in 20th-century sediments and reach unprecedented concentrations in sediments deposited after ca. A.D. 1980, tracking increasing summer temperatures in the absence of evidence for atmospheric nutrient subsidies. These results indicate that current warming in northern Greenland is unprecedented in the context of the past 2400 yr, and that climate change alone is responsible for the marked biological changes observed. [ABSTRACT FROM AUTHOR]

Sediments from Qipisarqo Lake provide a continuous Holocene paleoenvironmental record from southern Greenland. Following deglaciation and glacio-isostatic emergence of the basin from the sea ∼9100 cal yr B.P., proxies of lake paleoproductivity, including biogenic silica and organic matter, increased markedly until 6000 cal yr B.P. and thereafter remained stable over the ensuing warm three millennia. Subsequent decreases in these proxies, most dramatically between 3000 and 2000 cal yr B.P., show the lake''s responses to initial Neoglacial cooling. Intervals of ameliorated limnological conditions occurred between 1300 and 900 and between 500 and 280 cal yr B.P., briefly interrupting the decreasing trend in productivity that culminated in the Little Ice Age. Increased lake productivity during the latter half of the 20th century, which reflects the limnological response to circum-arctic warming, still has not reached peak Holocene values. The Neoglacial climate of the last 2000 yr includes the most rapid high-amplitude environmental changes of the past nine millennia. The Norse thus migrated around the North Atlantic Ocean region in the most environmentally unstable period since deglaciation. Lacustrine sediment records provide a context with which to consider future environmental changes in the Labrador Sea region. In particular, any future warming will be superposed on a regional climate system that is currently exhibiting highly unstable behavior at submillennial timescales. [Copyright &y& Elsevier]

The article explores whether spruce grew in southern Greenland during the Pleistocene period and thus provided evidence that the ice sheet was sufficiently reduced to allow for regional development of boreal forests. It says that there is independent evidence to prove that spruce lived in Greenland in the mid-Pleistocene. Meanwhile, it cites pollen data suggesting that the Greenland ice sheet was much smaller during previous warm periods. It predicts that the Arctic region will likely become warmer than it was during the Pleistocene period and will remain warmer for thousands of years if greenhouse gas concentrations continue to increase over the next century.

Background: Although arctic lakes have responded sensitively to 20(th)-century climate change, it remains uncertain how these ecological transformations compare with alpine and montane-boreal counterparts over the same interval. Furthermore, it is unclear to what degree other forcings, including atmospheric deposition of anthropogenic reactive nitrogen (Nr), have participated in recent regime shifts. Diatom-based paleolimnological syntheses offer an effective tool for retrospective assessments of past and ongoing changes in remote lake ecosystems., Methodology/principal Findings: We synthesized 52 dated sediment diatom records from lakes in western North America and west Greenland, spanning broad latitudinal and altitudinal gradients, and representing alpine (n = 15), arctic (n = 20), and forested boreal-montane (n = 17) ecosystems. Diatom compositional turnover (beta-diversity) during the 20(th) century was estimated using Detrended Canonical Correspondence Analysis (DCCA) for each site and compared, for cores with sufficiently robust chronologies, to both the 19(th) century and the prior approximately 250 years (Little Ice Age). For both arctic and alpine lakes, beta-diversity during the 20(th) century is significantly greater than the previous 350 years, and increases with both latitude and altitude. Because no correlation is apparent between 20(th)-century diatom beta-diversity and any single physical or limnological parameter (including lake and catchment area, maximum depth, pH, conductivity, [NO(3)(-)], modeled Nr deposition, ambient summer and winter air temperatures, and modeled temperature trends 1948-2008), we used Principal Components Analysis (PCA) to summarize the amplitude of recent changes in relationship to lake pH, lake:catchment area ratio, modeled Nr deposition, and recent temperature trends., Conclusions/significance: The ecological responses of remote lakes to post-industrial environmental changes are complex. However, two regions reveal concentrations of sites with elevated 20(th)-century diatom beta-diversity: the Arctic where temperatures are increasing most rapidly, and mid-latitude alpine lakes impacted by high Nr deposition rates. We predict that remote lakes will continue to shift towards new ecological states in the Anthropocene, particularly in regions where these two forcings begin to intersect geographically.

Concentrations and stable isotope ratios of lead (Pb) from lake sediments were used to quantify temporal patterns of anthropogenic Pb pollution in the Clyde River region of Baffin Island, Arctic Canada. Surface sediments from eight lakes on eastern Baffin Island and one from northern-most Greenland, spanning a gradient of 20 degrees latitude, showed great variability with respect to Pb concentration and stable isotopic Pb ratios, with little apparent latitudinal trend. To constrain the temporal evolution of regional Pb pollution, a well-dated core from one of the sites, Lake CF8 on east-central Baffin Island, was analyzed geochemically at high stratigraphic resolution. A pronounced decrease in the (206)Pb/(207)Pb ratio occurs in sediments deposited between 1923 and the mid-1970s, likely reflecting alkyl-Pb additives derived from the combustion of fossil fuels at a global scale. A two-component mixing model indicates that 17-26% of the Pb in the labile fraction of sediments deposited in Lake CF8 between 2001 and 2005 is from anthropogenic input. A Pb-Pb co-isotopic plot ((206)Pb/(207)Pb vs.(208)Pb/(206)Pb ratios) of the Lake CF8 time series data indicates multiple possible sources of industrial Pb pollution. Despite widespread reductions in industrial Pb emissions since the 1970s, there is no evidence for attendant reductions of pollution Pb at Lake CF8. Enhanced scavenging from increased primary production as well as changing precipitation rates as climate warms may represent important factors that modulate Pb deposition to Lake CF8, and Arctic lakes elsewhere.