The Chronology and Stratigraphy of the Little Ice Age

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The Chronology and Stratigraphy of the Little Ice
Age

• Presented by Sara Peek
• November 27, 2006

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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

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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.

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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

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Dendrochronology Lichenometry
Annual tree rings vary in thickness
Lichen Rhizocarpon geographicum increases in
radius over time
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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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Colonel Foster Glacier
The moraine complex is (i) two inner, relatively
barren, fresh-appearing moraines (Moraines 12),
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 35), with
the outermost of the three (Moraine 5) being the
most prominent and, (iii) an outer suite of
three smaller, forested moraines (Moraines 68).
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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.
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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

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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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Situation
The eastern lobe of the Caribou Glacier may spill
across a bedrock saddle to drain into Donard Lake
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Analysis of Annual Varves

• Objective Obtain annual climate record
• Method Analyze laminae in lake cores in
  conjunction with 14C dating and magnetic
  susceptibility

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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
Im not sure I like this plot.
(and trying to explain the variability with
rainfall records doesnt help much.)
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Reconstructed climate record
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Reconstructed climate record
Little Ice Age 1ºC lower than preceding period
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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

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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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55-m-high ice cliff at margin of Quelccaya ice
cap. Annual accumulation layers average ¾ m in
thickness.
1980 extent of Quelccaya Ice Cap
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Ice core stratigraphy
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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

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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

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Huaynaputina Little Ice Age
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Hows 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.

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Comparison
Southern and Northern hemisphere temperature
records are remarkably similar, implying a global
extent for the Little Ice Age.
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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 503517, 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 285297(2004)
• Lamb, H. H. 1977. Climate Present, Past and
  Future. Volume 2. Climatic history and future.
  Methuen, London
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