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Mullan Donal Swindles Graeme Patterson Tim Galloway Jennifer Macumber Andrew Falck Hendrik Crossley Laura Chen Jie Pisaric Michael 《Theoretical and Applied Climatology》2017,129(3-4):1089-1108
Theoretical and Applied Climatology - Climate models project that the northern high latitudes will warm at a rate in excess of the global mean. This will pose severe problems for Arctic and... 相似文献
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Kayla Deasley Jennifer B. Korosi Joshua R. Thienpont Steven V. Kokelj Michael F. J. Pisaric John P. Smol 《Journal of Paleolimnology》2012,48(2):287-296
An increase in the frequency and intensity of marine storm surges is a predicted consequence of climate warming, and therefore it is important to better understand the biological responses to such events in coastal regions. In late September 1999, a major storm surge resulted in a saltwater intrusion event over a large area of the Mackenzie Delta (NT, Canada) front, causing rapid salinization of lakes on the alluvial plain. Due to a lack of long-term ecological monitoring data in the region, the impacts that the saltwater intrusion event had on the biota of affected lakes were unknown. We used high-resolution paleolimnological approaches to reconstruct past assemblage changes in Cladocera from impacted Lake DZO-29 (unofficial name) in order to determine how different cladoceran species responded to a major increase in lake salinity following the 1999 storm surge. Camptocercus were extirpated from the lake following the saltwater intrusion and have not recovered. We also observed an initial decrease in Alona relative abundance following the marine flooding, likely reflecting a loss of A. quadrangularis, A. barbulata, and A. costata from the lake. A. circumfimbriata, Chydorus biovatus, C. brevilabris, and Bosmina spp. were abundant both before and after the saltwater intrusion, and Paralona pigra was present following the storm surge, but not prior to it. The most notable shift in Cladocera in the recent sedimentary record, however, occurred much earlier, with an increase in pelagic Bosmina taxa and a subsequent decrease in the benthic/littoral taxa Chydorus and Camptocercus, an assemblage shift that is consistent with a response to climate warming in this region, and strongly correlated to other changes in the lake inferred to be as a result of regional warming. 相似文献
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Michael F.J. Pisaric 《Journal of Paleolimnology》2002,28(3):349-354
Paleoecologists widely accept macroscopic plant remains preserved in lake sediment as good indicators of the vegetation communities growing within and adjacent to the margin of a lake or mire. However, the study of ash fallout from a small to moderate size forest fire in a low elevation Pseudotsuga menziesii/Pinus contorta/Abies lasiocarpa stand near Bozeman, Montana suggests that certain macroscopic plant remains can be transported long distances through the atmosphere. Conifer needles, pollen cones, cone scales, bracts and wood fragments were transported via the atmosphere and subsequently deposited at least 20 km from the forest fire. The majority of the plant remains that were identified were A. lasiocarpa needles. Pseudotsuga menziesii and P. contorta needles were also identified, but both were less abundant than A. lasiocarpa. The plant material that was recovered exhibited varying degrees of charring suggesting that it may be difficult to distinguish plant material that has been transported long-distances by forest fires from that which has been derived locally. Severe convection and vortices associated with intense forest fires are believed to be the primary mechanisms responsible for transporting plant material via the atmosphere. 相似文献
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We present a reconstruction of June–July minimum temperatures since AD 1245 for the Mackenzie Delta region based on a 29-site network of white spruce (Picea glauca) ring-width series. Most but not all trees experienced a divergent temperature–growth response, similar to the divergence that has affected other white spruce trees across Yukon and Alaska. However, divergence in the study region began as early as AD 1900 and we have documented our methods to avoid including divergent signals in the reconstruction. Calibration/verification testing based on local temperature data, and multi-century coherence with nearby and large-scale temperature proxy records, confirm that our reconstruction is robust. The reconstruction shows cool conditions in the late 13th, early 18th and early 19th centuries, corresponding with solar minima and increased volcanism. These cool periods are interrupted by warm periods consistent with early to mid-20th century warmth. The late 20th century is the warmest interval, and the last decade is estimated to be 1.4°C warmer than any decade before the mid-20th century. The reconstructed climate history corroborates other proxy-based inferences and supports the notion that high-latitude regions such as the Mackenzie Delta have experienced rapid warming in recent decades that is exceptional in the last eight centuries. 相似文献
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Vegetation assemblages and associated disturbance regimes are spatially heterogeneous in mountain ecosystems throughout the world due to the complex terrain and strong environmental gradients. Given this complexity, numerous sites describing postglacial vegetation and fire histories are needed to adequately understand forest development and ecosystem responses to varying climate and disturbance regimes. To gain insight into long-term historical climate–fire–vegetation interactions in southeastern British Columbia, Canada, sedimentological and paleoecological analyses were performed on a sediment core recovered from a small subalpine lake. The pollen assemblages, stomata, and macroremains indicate that from 9500 to 7500 cal yr BP, Pinus-dominated forests occurred within the catchment and Alnus was also present. Climate was an important control of fire and fire frequency was highest at this time, peaking at 8 fires 1000 yr− 1, yet charcoal accumulation rates were low, indicative of low terrestrial biomass abundance. From 7500 to 4600 cal yr BP, Pinus decreased as Picea, Abies and Larix increased and fire frequencies decreased to 3–6 fires 1000 yr− 1. Since 7500 cal yr BP the fire regime varied at a millennial scale, driven by forest biomass abundance and fuel accumulation changes. Local scale (bottom-up) controls of fire increased in relative importance since at least 6000 cal yr BP. 相似文献
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Diatom responses to 20th century climate-related environmental changes in high-elevation mountain lakes of the northern Canadian Cordillera 总被引：1，自引：0，他引：1
Tammy?L.?Karst-RiddochEmail author Michael?F.?J.?Pisaric John?P.?Smol 《Journal of Paleolimnology》2005,33(3):265-282
Diatom responses to 20th century climate-related environmental change were assessed from three high-elevation lakes in the northern Canadian Cordillera. Dominance of small benthic Fragilaria diatoms reflect the generally cold conditions with long periods of ice cover that have characterized these mountain lakes over at least the last ~300 years until the period of recent warming. At the turn of the 20th century, salient shifts in the diatom assemblages reveal individualistic limnological responses with the onset of climate warming trends in northwest Canada. At YK3 Lake, an oligotrophic, chemically dilute, alpine lake, increased representation of the planktonic Cyclotella pseudostelligera may reflect longer ice-free conditions and/or more stable thermal stratification. By contrast, in the more productive, alkaline lakes (BC2 and Deadspruce lakes), changes to more diverse assemblages of periphytic diatoms suggest greater benthic habitat availability, most likely associated with the enhanced growth of aquatic plants with lengthening of the growing seasons. In addition, diatom assemblages from these lakes suggest less alkaline conditions following the onset of 20th century climate warming. Continued alkalinity reduction throughout the 20th century is qualitatively inferred at the lower elevation, treeline lake (Deadspruce Lake), while greater representation of alkaliphilous Fragilaria diatoms after ~1950 suggested increased alkalinity at the alpine BC2 Lake. Our results confirm the sensitivity of diatoms from high-elevation mountain lakes to regional climate change in northwest Canada. Individualistic limnological responses to 20th century warming are potentially attributed to differences in their physical setting (e.g., bedrock geology, elevation, catchment vegetation) in this complex mountain environment. 相似文献
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Trevor J. Porter Michael F. J. Pisaric Robert D. Field Steven V. Kokelj Thomas W. D. Edwards Peter deMontigny Richard Healy Allegra N. LeGrande 《Climate Dynamics》2014,42(3-4):771-785
High-latitude δ18O archives deriving from meteoric water (e.g., tree-rings and ice-cores) can provide valuable information on past temperature variability, but stationarity of temperature signals in these archives depends on the stability of moisture source/trajectory and precipitation seasonality, both of which can be affected by atmospheric circulation changes. A tree-ring δ18O record (AD 1780–2003) from the Mackenzie Delta is evaluated as a temperature proxy based on linear regression diagnostics. The primary source of moisture for this region is the North Pacific and, thus, North Pacific atmospheric circulation variability could potentially affect the tree-ring δ18O-temperature signal. Over the instrumental period (AD 1892–2003), tree-ring δ18O explained 29 % of interannual variability in April–July minimum temperatures, and the explained variability increases substantially at lower-frequencies. A split-period calibration/verification analysis found the δ18O-temperature relation was time-stable, which supported a temperature reconstruction back to AD 1780. The stability of the δ18O-temperature signal indirectly implies the study region is insensitive to North Pacific circulation effects, since North Pacific circulation was not constant over the calibration period. Simulations from the NASA-GISS ModelE isotope-enabled general circulation model confirm that meteoric δ18O and precipitation seasonality in the study region are likely insensitive to North Pacific circulation effects, highlighting the paleoclimatic value of tree-ring and possibly other δ18O records from this region. Our δ18O-based temperature reconstruction is the first of its kind in northwestern North America, and one of few worldwide, and provides a long-term context for evaluating recent climate warming in the Mackenzie Delta region. 相似文献
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Lindsay M. Upiter Jesse C. Vermaire R. Timothy Patterson Carley A. Crann Jennifer M. Galloway Andrew L. Macumber Lisa A. Neville Graeme T. Swindles Hendrik Falck Helen M. Roe Michael F. J. Pisaric 《Journal of Paleolimnology》2014,52(1-2):11-26
We analyzed subfossil chironomids, sediment organic matter and sediment particle size data from a 1.11-m-long freeze core collected from Carleton Lake (unofficial name), located approximately 120 km north of the modern treeline. This well-dated core spans the last ca. 6,500 years. Two chironomid transfer functions were applied to infer mean July air temperatures. Our results indicated that the chironomid-inferred temperatures from this lake sediment record did not pass a significance test, suggesting that other factors in addition to temperature may have been important in structuring the chironomid community through time. Although not statistically significant, the chironomid-inferred temperatures from this site do follow a familiar pattern, with highest inferred temperatures occurring during the Holocene Thermal Maximum (~6–4 cal kyr BP), followed by a long-term cooling trend, which is reversed during the last 600 years. The largest change in the chironomid assemblage, which occurred between ca. 4,600 and 3,900 cal yr BP is possibly related to the well-documented northward advance and subsequent retreat of treeline in this region. 相似文献