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?

Possible Causes Reduced solar intensity 14 C and 10 Be, as well as medieval sunspot counting, proxy for solar intensity

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?

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 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

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

Septimus Glacier

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

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 14 C dating and magnetic susceptibility 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

--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.)

Reconstructed climate record

Little 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

Quelccaya Ice Cap: Largest Glacier in Peru

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.

Ice core stratigraphy

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

How’s the accuracy? For the post-1500 AD record, the authors give the uncertainty as ±2 years, with an absolute date at 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 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.

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 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, 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 Climate & Present, Past and Future. Volume 2. Climatic history and future. Methuen, London