Geoscience Reference
In-Depth Information
Abrupt Climate Changes During the Holocene Across North America
From Pollen and Paleolimnological Records
Konrad Gajewski and Andre E. Viau
Laboratory for Paleoclimatology and Climatology, Department of Geography, University of Ottawa, Ottawa, Ontario, Canada
Databases of ecological and cultural records, especially of pollen diagrams,
record climate variability of several time scales during the Holocene and late
glacial. Results from lake and wetland ecosystems geographically extend the
evidence of rapid climate change obtained from ice cores and ocean sediments.
Continental and regional climate curves for North America, based on pollen
diagrams from the North American Pollen Database, illustrate abrupt changes on
the order of every ~1000 years during the past 12 kyr, and major times of change in
North American pollen records are coherent with vegetation changes across
Europe. Novel analyses of the database show that even taxa that are widespread
and with presumably broad climate tolerances were affected by abrupt climate
changes such as the Younger Dryas and illustrate the complexity of ecosystem
response to these changes. Reconstructions of freshwater as well as terrestrial
ecosystems across northern Canada also show how climate variability affects
terrestrial and freshwater ecosystem-level properties such as nutrient cycling. These
results can be used to reconstruct the spatial patterns of abrupt climate change, as
well as the impacts of climate change on ecosystem and cultures.
1. INTRODUCTION
1988; Dansgaard et al., 1993; Rahmstorf, 2003]. However,
one major uncertainty that arises in paleoclimate research
is the lack of spatial corroborating evidence. For example,
the Greenland ice core records offer a temporal record of past
climate variations on several time scales; however, they
remain a single point in space until results can be compared
to records found in other regions. This lack of the spatial
dimension has plagued large-scale paleoclimate research for
many years. The last few decades have seen assembled large
databases of paleoclimate information. The availability of
large databases of pollen, tree ring, and other data enables
syntheses of the terrestrial paleoclimate at several time and
space scales.
Considerable progress has been achieved in the past 30
years in producing paleoclimate estimates for the postglacial
using pollen as a climate proxy for all of North America and
Europe. This has come about due to the availability of a
critical mass of fossil and calibration data and methodolog-
ical developments suitable for large-scale reconstructions,
paleoclimate time series are
from ocean [e.g., Imbrie et al., 1989] or ice cores [e.g.,
Johnsen et al., 2001; EPICA Members, 2006], a considerable
amount of information is known about the terrestrial paleo-
climates of the past 21 kyr [e.g., Bryant and Holloway, 1985;
Wright et al., 1993]. Evidence from marine and ice cores
suggests abrupt climate changes superimposed on the
Although most of the
iconic
variability that occurred throughout
the last million years [e.g., Bond et al., 1997, 2001; MacMa-
nus et al., 1999; O
Milankovitch-scale
Brien et al., 1995; Oppo et al., 1998;
Raymo et al., 1998; Bianchi and McCave, 1999; Heinrich,
'
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