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Journal ArticleDOI: 10.1177/0959683614556376

Diatom-based evidence of regional aridity during the mid-Holocene period in boreal lakes from northwest Ontario (Canada)

01 Jan 2015-The Holocene (SAGE Publications)-Vol. 25, Iss: 1, pp 166-177
Abstract: Boreal regions and their freshwater ecosystems may be susceptible to future climate change under projected warmer conditions. Northwest Ontario is a boreal region adjacent to the climatically sensitive prairie-forest ecotone (PFE). Pollen records spanning the Holocene from near the Manitoba/Ontario border to lakes up to ~300 km east of the PFE indicate a warmer and possibly wetter mid-Holocene period across northwest Ontario from ~8000 to 4500 cal. yr BP. To date, only one Holocene-scale record of changes in effective moisture, as indicated through diatom-inferred changes in lake level (Experimental Lakes Area (ELA) Lake 239), is available from this region. Our study expands the regional context of Holocene climate changes, with the analysis of diatom assemblages in sediment cores from two additional lakes, which span a distance of over 200 km across the present-day boreal forest, from 80 km west of ELA Lake 239 to ~150 km to the northeast. In cores from both lakes, benthic taxa predominate in the early-to-mid-Holocene period, with a low abundance of planktonic taxa, suggesting lower lake levels by ~2–5 m. Increases in the abundance of planktonic taxa to >50% occurred in both lakes beginning ~4500–4000 cal. yr BP suggesting positive water balance over the last 4000 years in comparison with the mid-Holocene period. This new evidence supports a regional mid-Holocene period of aridity, with reduced water levels across the boreal region of northwest Ontario. If future climate change results in lower effective moisture, then conditions could become similar to the mid-Holocene period aridity, leading to real challenges for the management of water resources across the region. more

Topics: Boreal (57%), Holocene (55%), Freshwater ecosystem (51%)

Open accessJournal ArticleDOI: 10.1002/ECS2.2287
01 Jun 2018-Ecosphere
Abstract: The North American boreal forest has been developing since the end of the last glaciation approximately 10,000 yr ago. With climate warming and human occupation, it is anticipated that fire danger, ignition, and activity will be increasing, compromising forests’ benefits for generations to come. In this study, we show, however, that a century of rapid climate changes and human densification has had the opposite effect in the boreal eastern interior of the North American continent, reducing biomass burning to values below two millennia of historical levels. A multi-millennial fire history was reconstructed for eight forested landscapes from the Lake of the Woods Ecoregion (LWE) located at the boreal–prairie ecotone. Fire history was reconstructed using a combination of archival (period 1920–2010), tree-ring (stand initiations and fire scars: period 1690–2010), and lake sediment charcoal (2500 BP to present) records. The archival record revealed recent large fires (>200 ha) in 1948, 1980, and 1988. An additional 19 fires were identified by the fire-scar record. Fire events in 1805, 1840, 1863, and the 1890s were identified in numerous locations around multiple lakes suggesting that they were of large extents. In accordance with the tree-ring record, the charcoal accumulation rate (CHAR) peak record generally identified the major fires but tended to lag from the tree-ring records by several decades. Within LWE, the long-term charcoal record revealed that CHAR was higher for each lake in the earlier portion of the record including the warm Medieval Climate Anomaly (AD 900 to AD 1000), followed by a progressive decrease toward the cool Little Ice Age period. This decline was abruptly interrupted in the midto late 19th century with large synchronized fires, also reported over western and central North America, and resumed approximately four decades later. Fire disturbance level is today below the historical range, despite the accentuated climate warming. Aging of the forest landscape may create biodiversity loss notably in fire-adapted species while at the same time setting the tone for major fires in upcoming decades if no action is taken for managing fuels. more

Topics: Boreal (58%), Paleoecology (55%), Climate change (51%)

9 Citations

Journal ArticleDOI: 10.1016/J.QUASCIREV.2015.06.025
Abstract: This study investigates regional changes in primary producers in boreal head-water lakes during the warmer early-to-mid-Holocene (EMH) period, across the present-day boreal forest in northwest Ontario, a region that is adjacent to the prairie-forest ecotone. We quantified changes in algal abundance and composition over the Holocene period using pigments, spectrally-inferred chlorophyll a and diatom assemblages in well-dated sediment cores from three lakes. All three indicators showed a coherent pattern of enhanced primary producers in two of the study lakes (Gall Lake and Lake 239) during the EMH, whereas only diatom assemblages suggested higher levels of nutrients in Meekin Lake. Overall, this study supports a regional pattern of enhanced primary producers during the EMH, likely as a function of lower water-levels and warmer temperatures. Elevated concentrations of cyanobacterial pigments also occurred in two of the three lakes during the EMH, whereas pigments from purple-sulphur bacteria provide evidence of enhanced deep-water anoxia in one lake. These findings suggest that future climatic warming in boreal regions could include regional eutrophication and associated increases in cyanobacteria. more

Topics: Boreal (53%), Eutrophication (51%), Primary producers (51%) more

6 Citations

Open accessJournal ArticleDOI: 10.1088/1748-9326/AB59C9
Abstract: Climate changes are expected toprogressively increase extremewildfire frequency in forests. Findingpast analogs for periodsof extremebiomass burningwouldprovide valuable insights regardingwhat the effects ofwarmingmight be for tree speciesdistribution, ecosystem integrity, atmospheric greenhouse gas balance, andhuman safety.Here,weused anetworkof 42 lake-sediment charcoal records across a∼2000 km transect in easternborealNorthAmerica to inferwidespreadperiodsofwildfire activity in associationwith past climate conditions.The reconstructedfluctuations inbiomassburning arebroadly consistentwith variations in ethane concentration inGreenlandpolar ice cores.Biomassburningfluctuations also significantly co-variedwithGreenland temperatures estimated from ice cores, at least for thepast 6000 years.Our retrospective analysis of pastfire activity allowedus to identify twofire periods centered around 4800 and1100BP, coincidingwith large-scalewarming innorthern latitudes andhaving respectively affected an estimated∼71%and∼57%of the study area.These twoperiods co-occurredwithwidespread decreases inmeanfire-return intervals.The twoperiods are likely thebest analogs forwhat couldbe anticipated in termsof impacts offireonecosystemservices providedby these forests in comingdecades. more

Topics: Boreal (56%)

5 Citations


Open accessJournal ArticleDOI: 10.2458/AZU_JS_RC.55.16947
Paula J. Reimer1, Edouard Bard2, Alex Bayliss3, J. Warren Beck4  +26 moreInstitutions (20)
01 Jan 2009-Radiocarbon
Abstract: Additional co-authors: TJ Heaton, AG Hogg, KA Hughen, KF Kaiser, B Kromer, SW Manning, RW Reimer, DA Richards, JR Southon, S Talamo, CSM Turney, J van der Plicht, CE Weyhenmeyer more

13,118 Citations

Open access
01 Jan 2002-
Abstract: Canoco is a software package for multivariate data analysis, with an emphasis on dimesional reduction (ordination), regression analysis, and the combination of the two, constrained ordination. Canoco makes effective and powerful ordination methods easilyt accessible for scientists wanting to infer and visualize pattern and structure in complex multivariate data, e.g. biologists researching the relations between plant and animal communities and their environment. Canoco contains linear and unimodal ordination methods, with the possibility to account for background variation specified by covariates. In combination with extensive facilities for permutation tests, these methods have proven to be remarkably effective in solving applied research problems. more

Topics: Ordination (58%)

7,472 Citations

Abstract: A modified ignition loss method is described for determining organic and carbonate carbon in calcareous sedimentary materials using equipment found in most laboratories. The method has been found to equal or excel the accuracy and precision of other methods tested and has the advantage of being considerably faster if large numbers of samples are to be analyzed. more

Topics: Carbonate (60%), Calcareous (58%), Loss on ignition (55%) more

2,770 Citations

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