Younger Dryas Paleoclimate Data; GISS, NY
Entry ID:
EARTH_LAND_GISS_Paleocl_Dryas1
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Summary
Younger Dryas Data - Paleoclimate Evidence of Rapid Climate Change
Evidence of past climate change provides a historical perspective from
which we may view our present and future climate. Records derived from
ice cores, lake, bogs, ocean sediments, and glacial moraines indicate
that our climate has changed considerably over the last 20,000
years. ... As paleoclimate techniques have improved and enhanced
resolution magnifies our view, it is now obvious that the climate has
changed frequently and rapidly in the past, both from warm to cold
conditions and from cold to warm. The most prominent of these
reversals is the Younger Dryas cooling that was first discovered in
Europe, and occurred refers to the Arctic-Alpine flower, Dryas.
Fossils of this plant and other tundra indicators were found
sandwiched between sediments that indicated warmer, forested
environments.) We may ask, does closer scrutiny of this event tell us
anything that is relevant to our future? We know that describing the
past patterns of change will aid us in understanding how rapidly
vegetation can respond to climate change, and ultimately, what may be
causing change.
Studies at GISS have resulted in the discovery of a similar event
in North America. This event has now been examined in three lakes
and swamps in southern New England, using a combination of pollen
stratigraphy, macrofossil stratigraphy, and accelerator mass
spectrometry (AMS) techniques. We are looking closely at the
patterns of vegetational change in the rapid warming and cooling
modes.
In the northeastern U.S., the Younger Dryas event is regionally
apparent from pollen records that indicate a change from a mixed
hardwood deciduous forest (oak, ash, spruce, fir) to a boreal
assemblage (spruce, fir, larch, birch, alder) as seen in pollen
zones A-3 and A-4 in the first figure. Subsequently, the pollen
assemblage dramatically reverses, as the boreal components
disappear and, first, white pine, then oak, dominates. This pattern
of pollen assemblage zones is recorded in over 20 sites in the
northeastern U.S. Three questions were asked concerning this change
in regional pollen stratigraphy to determine whether this change
represented a climatic change similar to that found in Europe: (1)
Does this palynological change represent a real change in
vegetation, as opposed to a change in wind direction? (2) Was the
vegetational change due to changes in climate? (3) What were the
timing and rate of the vegetational change?
To determine whether the palynological change represented a true
vegetational change, sediment samples were screened for
macrofossils (leaves, needles, seeds), which give a more precise
determination of the species involved. In addition, macrofossils
are important because, although pollen may blow long distances, the
macrofossils indicate the actual vegetation at the site. The
results of this detailed analysis indicated that the distribution
of boreal trees indeed expanded during this interval, and that
trees with such northerly distributions as paper birch replaced
warmer species such as white pine. The winters during this time
must have been severe, as increased alder and paper birch indicate
disturbance. The magnitude of the change in the NY-CT-NJ region was
a cooling of about 3 to 4 xC annually, and the snow depth was
probably considerably more than present. Extreme winters probably
left gaps in the forest that were filled by light-demanding paper
birch and alder. Determination of the timing of the dramatic
northeastern U.S. cooling and the subsequent warming is important
for correlation with the European event, as well as for comparison
with ice core and marine records, and other regional land
records. The macrofossils were submitted for AMS dating to Lawrence
Livermore Laboratories in California, where analysts there are able
to determine the (14)C age of a single spruce needle. Results of
the dating indicated that the cooling occurred between 11,000 and
10,000 years ago, which proves that the event here in southern New
England is the same as that in Europe, in the Greenland ice cores,
and in North Atlantic marine records.
From the 5-cm detailed analysis of the sedimentation rates in the
sediment cores, estimates of the regional vegetational change rates
were made. The best estimates are that the climate change at the
onset of the cooling took place over about 100 to 200 years. The
close of the Younger Dryas cooling, typified by a vegetation change
from boreal trees to a warmer white pine and oak forest, took place
over an interval of between 50 and 150 years. From the macrofossil
changes, it is evident that trees such as spruce, fir, and paper
birch became locally extinct at the time of this rapid warming, and
have remained absent from this region for the past 10,000
years. This dramatic and rapid change is comparable to that
predicted for future greenhouse warming, and is comparable to the
report of a very sharp transition (50 to 100 years) for this period
in the Greenland ice cores.
With two data points in-hand, it is now reasonable to inquire as to
the global distribution of this event. At GISS, we are continuing
to assess the available evidence for this reversal worldwide
through continued literature compilation as well as field work. If
indeed the methane and carbon dioxide decreases in the ice cores
are linked in age to the Younger Dryas interval, it means that the
event was global, because these gases are distributed rapidly in
the atmosphere. Based upon North Atlantic evidence of cooling, in
1986 we reported the GCM results of the effects of a colder North
Atlantic over land regions adjacent to the North Atlantic, as shown
in the second figure, which agrees with terrestrial paleoclimatic
evidence from the North Atlantic region. However, we are
continuing to assess reports of the Younger Dryas in locations
further afield, specifically with a research program of glacial
geology and palynology at high latitudes, including Kodiak Island,
Alaska.
Results from Kodiak Island suggest that glacial advances and
vegetational changes characterized the interval from 11,000-10,000
years BP. We are currently identifying the vegetational changes
during this period, but it appears that a major regional cooling
did take place roughly during this time interval, as evidenced by
the decline of warmth-demanding ferns and the increase of
tundra. Additional AMS dating of macrofossils should tell us
whether a major change took place that is correlative with the
Younger Dryas of Europe and eastern North America.
We are continuing our modeling efforts from the latest data-model
interaction. We have conducted additional GCM experiments using
new marine data that indicate a 2 xC cooling in North Pacific sea
surface temperature during the Younger Dryas. The resulting annual
air temperature difference between today and this experiment is
quite large throughout the Northern Hemisphere, including the air
temperature over North America and Europe. This result is
significant because it points to the tremendous impact of the large
area of the North Pacific Ocean on northern hemispheric climate
when the temperature is lowered, as less moisture in the air
results in less of a greenhouse warming effect.
We continue to delve into the questions of the distribution,
timing, magnitude, and vegetational expression of this rapid and
major climate event of the past. By analyzing its effects
regionally and globally, we will be in a better position to define
the cause of such rapid climate changes, and our future.
for more information, see:
http://www.giss.nasa.gov/research/paleo/
and
http://www.giss.nasa.gov/research/intro/peteet_01/
Geographic Coverage
Spatial coordinates
Data Set Citation
Dataset Creator:
PETEET, D
Dataset Title:
Younger Dryas Paleoclimate Data; GISS, NY
Online Resource:
http://www.giss.nasa.gov
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Paleo Temporal Coverage
Location Keywords
Science Keywords
ISO Topic Category
Platform
Ancillary Keywords
Originating Center
Data Center
Personnel
DOROTHY
M.
PETEET
Role:
INVESTIGATOR
Email:
Dorothy.M.Peteet at nasa.gov
Contact Address:
NASA
Goddard Space Flight Center
Mailstop 611.0
City:
Greenbelt
Province or State:
MD
Postal Code:
20771
Country:
USA
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Publications/References
Peteet, D. 1995. Global Younger Dryas? Quaternary Intl. 28, 93-104.
Creation and Review Dates
Last DIF Revision Date:
2005-08-09
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Links
