22 research outputs found
Abrupt climate change as an important agent of ecological change in the Northeast U.S. throughout the past 15,000 years
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Quaternary Science Reviews 28 (2009): 1693-1709, doi:10.1016/j.quascirev.2009.04.005.We use a series of tests to evaluate two competing hypotheses about the association of climate
and vegetation trends in the northeastern United States over the past 15 kyrs. First, that abrupt
climate changes on the scale of centuries had little influence on long-term vegetation trends,
and second, that abrupt climate changes interacted with slower climate trends to determine the
regional sequence of vegetation phases. Our results support the second. Large dissimilarity
between temporally-close fossil pollen samples indicates large vegetation changes within 500
years across >4° of latitude at ca. 13.25-12.75, 12.0-11.5, 10.5, 8.25, and 5.25 ka. The evidence of
vegetation change coincides with independent isotopic and sedimentary indicators of rapid
shifts in temperature and moisture balance. In several cases, abrupt changes reversed long-term
vegetation trends, such as when spruce (Picea) and pine (Pinus) pollen percentages rapidly
declined to the north and increased to the south at ca. 13.25-12.75 and 8.25 ka respectively.
Abrupt events accelerated other longâterm trends, such as a regional increase in beech (Fagus)
pollen percentages at 8.5-8.0 ka. The regional hemlock (Tsuga) decline at ca. 5.25 ka is unique
among the abrupt events, and may have been induced by high climatic variability (i.e., repeated
severe droughts from 5.7-2.0 ka); autoregressive ecological and evolutionary processes could
have maintained low hemlock abundance until ca. 2.0 ka. Delayed increases in chestnut
(Castanea) pollen abundance after 5.8 and 2.5 ka also illustrate the potential for multi-century
climate variability to influence speciesâ recruitment as well as mortality. Future climate changes
will probably also rapidly initiate persistent vegetation change, particularly by acting as broad,
regional-scale disturbances.This work was supported by NSF grants to B. Shuman (EARâ0602408; DEBâ0816731) and J.
Donnelly (EARâ0602380)
High methylmercury in Arctic and subarctic ponds is related to nutrient levels in the warming eastern Canadian Arctic
Permafrost thaw ponds are ubiquitous in the eastern
Canadian Arctic, yet little information exists on their potential as
sources of methylmercury (MeHg) to freshwaters. They are
microbially active and conducive to methylation of inorganic
mercury, and are also affected by Arctic warming. This multiyear
study investigated thaw ponds in a discontinuous permafrost region
in the Subarctic taiga (Kuujjuarapik-Whapmagoostui, QC) and a
continuous permafrost region in the Arctic tundra (Bylot Island,
NU). MeHg concentrations in thaw ponds were well above levels
measured in most freshwater ecosystems in the Canadian Arctic
(>0.1 ng Lâ1). On Bylot, ice-wedge trough ponds showed
significantly higher MeHg (0.3â2.2 ng Lâ1) than polygonal
ponds (0.1â0.3 ng Lâ1) or lakes (<0.1 ng Lâ1). High MeHg was
measured in the bottom waters of Subarctic thaw ponds near
Kuujjuarapik (0.1â3.1 ng Lâ1). High water MeHg concentrations in thaw ponds were strongly correlated with variables
associated with high inputs of organic matter (DOC, a320, Fe), nutrients (TP, TN), and microbial activity (dissolved CO2 and
CH4). Thawing permafrost due to Arctic warming will continue to release nutrients and organic carbon into these systems and
increase ponding in some regions, likely stimulating higher water concentrations of MeHg. Greater hydrological connectivity
from permafrost thawing may potentially increase transport of MeHg from thaw ponds to neighboring aquatic ecosystems
Structure des peuplements, rĂ©gimes de perturbation et dynamiques de succession dans les forĂȘts borĂ©ales eurasiennes : une revue basĂ©e sur des travaux russes
LâObservatoire Homme-Milieux international NUNAVIK : le fondement dâune recherche multidisciplinaire, sectorielle et communautaire au QuĂ©bec septentrional.
National audienc
Paaliup Qarmangit 1 site geoarchaeology Taphonomy of a Thule-Inuit semi-subterranean dwelling in a periglacial context in northeastern Hudson Bay
International audienc