The Chronology and Stratigraphy of the Little Ice Age Presented by Sara Peek November 27, 2006.
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Transcript of The Chronology and Stratigraphy of the Little Ice Age Presented by Sara Peek November 27, 2006.
Overview Background Use of dendrochronology and
lichenometry to date coarse warming Varved sediments provide a more
continuous climate record Ice core records imply a worldwide
event
Background What is the Little Ice Age?
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Possible Causes Reduced solar intensity
14C and 10Be, as well as medieval sunspot counting, proxy for solar intensity
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Possible Causes Increased volcanic activity
Ash clouds block solar radiation; some cooling can persist for 2 years after the eruption
Sulfuric acid in the stratosphere can also reflect sunlight, resulting in further cooling.
Warming Did the Little Ice Age end because of
the Industrial Revolution?
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Overview Background Use of dendrochronology and
lichenometry to date coarse warming Varved sediments provide a more
continuous climate record Ice core records imply a worldwide
event
Dendrochronology & Lichenometry
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Annual tree rings vary in thickness
Lichen Rhizocarpon geographicum increases in radius over time
Dendrochronology & Lichenometry
Objective: Date moraines, which can be a proxy for climate shift, associated with the Little Ice Age
Methods: Counting tree rings and measuring lichen radii
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The moraine complex is (i) two inner, relatively barren, fresh-appearing moraines (Moraines 1–2), the second of which (Moraine 2) is considerably larger and overrides the proximal face of Moraine 3; (ii) a middle suite of three sparsely lichen and tree-covered moraines (Moraines 3–5), with the outermost of the three (Moraine 5) being the most prominent; and, (iii) an outer suite of three smaller, forested moraines (Moraines 6–8).
Colonel Foster Glacier
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Septimus Glacier
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Results
The year associated with each moraine denotes the year that the glacier began to recede; that is, years that climate was warming.
Overview Background Use of dendrochronology and
lichenometry to date coarse warming Varved sediments provide a more
continuous climate record Ice core records imply a worldwide
event
The Varved Sediments of Donard Lake
Donard Lake is located in a trough of the global-scale west winds
Warming or cooling changes the position of the trough, so the region is very sensitive to climate shifts
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The eastern lobe of the Caribou Glacier may spill across a bedrock saddle to drain into Donard Lake
Situation
Objective: Obtain annual climate record
Method: Analyze laminae in lake cores in conjunction with 14C dating and magnetic susceptibility
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Analysis of Annual Varves
Analysis Numerous studies have shown that
runoff and suspended sediment are a function of summer temperature
Thus, with calibration from historical records, varve thickness is can be used as a climate proxy
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--Solid line is varve thickness
--Dotted line is summer temperature
I’m not sure I like this plot.
(and trying to explain the variability with rainfall records doesn’t help much.)
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Reconstructed climate record
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Reconstructed climate recordLittle Ice Age: 1ºC lower than preceding period
Overview Background Use of dendrochronology and
lichenometry to date coarse warming Varved sediments provide a more
continuous climate record Ice core records imply a worldwide
event
Stratigraphy of the Quelccaya ice cap
Objective: reconstruction of a 1.5kyr climatic record
Methods: isotope, conductivity, and microparticle analysis of ice cores
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Quelccaya Ice Cap: Largest Glacier in Peru
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1980 extent of Quelccaya Ice Cap
55-m-high ice cliff at margin of Quelccaya ice cap. Annual accumulation layers average ¾ m in thickness.
Why dust layers? During the dry season, sublimation
concentrates top-level particulates Dominant dry-season wind blows west
or north-west off the dry Peruvian altiplano (plateau).
Faster dry-season winds
Huaynaputina Largest recorded volcanic eruption in
Peru Dates are known precisely to February
and March of 1600 AD
Thus, the thick dust layer from the eruption can be used to place the climate record in time
Huaynaputina & Little Ice Age
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How’s the accuracy? For the post-1500 AD record, the
authors give the uncertainty as ±2 years, with an absolute date at 1600.
However, for the lowest part of the core, only visible dust layers could be used for dating, so uncertainty goes up to an estimated ±20 years.
Comparison
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Southern and Northern hemisphere temperature records are remarkably similar, implying a global extent for the Little Ice Age.
Conclusions A variety of climate proxies show the
Little Ice Age to be both a significant and a worldwide event.
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References Thompson, L.G., et. al. The Little Ice Age recorded in the stratigraphy of the Quelccaya ice
cap. Science, Vol. 234, No. 4774, pgs 361-364. 1986. Moore, J.J., et. al. Little Ice Age recorded in summer temperature reconstruction from
varved sediments of Donard Lake, Baffin Island, Canada. Journal of Paleolimnology 25: 503–517, 2001.
Lewis, D.H., and D.J. Smith. Little Ice Age glacial activity in Strathcona Provincial Park, Vancouver Island, British Columbia, Canada. Can. J. Earth Sci. 41: 285–297(2004)
Lamb, H. H. 1977. Climate & Present, Past and Future. Volume 2. Climatic history and future. Methuen, London
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