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UNIT D: HUMAN ENVIRONMENT INTERACTION PALEOCLIMATOLOGY Photo Credit: Emily Niederman Given Assumptions  Law of Uniformitarianism  Assumption that the way observed processes work currently are the same way in which they worked in the past.  (processes don’t change)  Law of Superposition  Laminations (layers) can be ordered from the bottom being the oldest and the youngest being the top.  (each layer is a period of time) What is Paleoclimatology?  Reconstruction of climate over the history of the Earth  The study of past climates prior to the instrument record  Most research devoted to past 2 million years  And most of that research devoted to past 10 thousand Why Study Past Climates?  Study of paleoclimate crucial to understanding future climates  What is abrupt climate change?  How has the Earth reacted before? Warm Cold Warm Problems with Weather Records  Weather records only go back ~150 years (~1860)  Often less than 50 years  Natural climate oscillations can be 10s or 100s of years  Misleading information: Water resources for American West divided during abnormally wet period Problems with Weather Records  American West  Now we are in normal-to-dry period, there isn’t as much water as was promised by weather records Quick History of the Recent Climate  Over 11 glacial cycles over past 2 million years  Most recent ended ~12,000 years ago  No reason to expect cycles to end (aside from humaninduced warming) Quick History of the Recent Climate  Temperatures fluctuate by less than 1 degree Celsius (~0.7 ° C) worldwide average in Holocene (modern interglacial)  Precipitation changes often drastic Getting the Record   Weather Records: ~150 years Modern Scientific Theory: Billions of years   Archives   How do we fill in the gap? A geophysical or biological chronological record containing proxies to interpret past environments Proxies  A chemical or physical feature that varies due to a climatic factor as found chronologically in an archive Proxies Proxies Tree rings Lake varves (sediments) Speleothems Coral (from cave) (annual growth) Ice Core ANNUAL RECORDS OF THE PAST Proxy Oxygen Isotope  The most common element used in climate studies is oxygen!  Oxygen has two isotopes of concern:  16O  18O  is by far most common (99.76%) is our focus (0.24%) The ratio of 18O to 16O (δ18O) in water changes according to different rainfall amounts and temperature Greater δ18O values during drier conditions  Less δ18O values during wetter conditions  Ice Cores Ice Cores  Go back 2 million years  Collected from Greenland and Antarctica  High Mountain Glaciers as well  Looking for δ18O (to check drier/wetter conditions)  Dust trapped in ice  More  dust = windier & drier conditions Speleothems  Cave water Dripstones  Stalagmites/Stalactites  Created in caves from dripping rainwater  Layering preserves record  Looking for δ18O (to check drier/wetter)  Crystal structure changes Lake Levels  Lakes with no outlet rise & fall with changes in rainfall amount  More rain = raises lake level  Less rain = lowers lake level Sand Dunes  Active sand dunes exist in drier conditions  Wetter conditions promote vegetation & stabilize Pollen Records  Pollen is tiny reproductive cells of plants  Can identify what type of plants it came from Preserved in sediment layers in the bottoms of ponds, lakes, or oceans  Pollen Records  Some plants associated with drier, grassy environment  Other plants associated with wetter, forested environment  Create a ratio where = more dry-associated (wetassociated) plants = drier (wetter) conditions! Multi-proxy Approach  Best to combine several methods & records based on different proxies  They will never match perfectly!  Have to decide what looks significant and comparable Plot & Compare neutral 35 30 Average Value Drier → 25 20 Record A Record B 15 Record C 10 5 0 2000 1900 1800 1700 1600 1500 1400 1300 Year (AD) 1200 1100 1000 900 800 700 600 drier wette Workbook Tips & Tricks  A lot of plotting, but simple  Check to see whether greater value = drier first!  Some periods can be neither wet nor dry if they float around the average  Some of your conclusions may be slightly different than others  But such is science! Research Motivation 4200 cal yr BP event (Winner, 2012) Characterize regional hydroclimate variability during the mid- to late Holocene in northern India. Research Goals a. Determine if evidence for a 4200 cal yr BP event is present at the site b. Compare developed paleoclimate record with the Harappan “metamorphosis”  Protected Site (Uttarakhand Forestry Dept.) Vegetation  Temperate vegetation  Mainly oak (Quercus semecarpifolia) with other trees  Shrubs and grasses as well  Aquatic Plant  Littoral (shallows)  Genus: Trapa (Porinchu 2018) “water chestnuts” (Niederman 2019) Research Methods  Core Recovery  Livingstone Corer  Stratigraphy  Chronology: radiocarbon dating  Non-destructive Radiography  pXRF  X-Ray Radiographs  CT Scans (Porinchu 2018) Age-Depth Model  Eleven 14C dates: Age  Ten 14C dates from core (blue)  One modern Trapa seed case → modern carbon  Bayesian Accumulation Model (BACON; Blaauw & Christen 2011) Depth Non-destructive, Radiological Approaches X-ray Fluorescence (XRF)  Handheld device mounted on a core scanner  Elemental component analysis  Displaces electrons via X-rays and records the returning fluorescence (Niederman 2019) Non-destructive, Radiological Approaches X-ray Imaging  Grey-scale image  Trapa location identification & stratigraphy Computerized Tomography (CT) scans  High resolution imaging  3D model based on stacked X-ray images  HU numbers (radiodensity on Hounsfield Scale) Radiology and Imaging Department (Niederman 2019) Interpretation Proxy HU # PCA 1 Fe/Mn Th & Ti PCA2 Increase Volume (Wet) Decrease Volume (Dry) Related Mechanism / Driver Method Instrumentation (Fritz et al., 2018) CT (Davies et al., 2015) XRF Detrital Influx. Measuring radiodensity. Denser sediment requires more energy for transport. Detrital Influx. (K, Ti, Re, Rb, Sr, Th). Elements associated with Detrital Influx. Lake Bottom Water Oxygenation. (Cuven et al., 2011) Redox. Fe precipitates before Mn in anoxic conditions. Deeper lakes → less mixing → more anoxic. (Davies et al., 2015) Detrital Influx. Elements associated with Detrital Influx. Th based with correlation. Lake Bottom Water Oxygenation. (Cuven et al., 2011) (Fe/Mn, Mn). Elements associated with Redox. XRF XRF XRF Results  Four events (centered):     4850 cal yr BP (major) 4200 cal yr BP (major) 3500 cal yr BP (minor) 3100 cal yr BP (major)  Blue Bands (Wet)  Yellow Bands (Dry)  4200 cal yr BP: Wet then Dry  3100 cal yr BP: Dry than Wet YOUNGER OLD Environmental Interpretation 4200 cal yr BP  Wet: 4350 – 4200 cal yr BP  Dry: 4200 – 4050 cal yr BP 3100 cal yr BP  Dry: 3100 – 3000 cal yr BP  Wet: 3200 – 3100 cal yr BP Sand Lens Abdomen X-ray Discussion: The Harappa Phase cal yr BP Harappan Description Paleoenvironmental (Leipe et al., 2014) Record – Before 5200 – Relatively wetter than DRL-1 (Giosan et al., 2012)  Floodplain agricultural system Early 5200 4500 Winter Crops (wheat, barley) 4850 cal yr BP event  Never developed canals or other irrigation systems Mature 4500 3900 Urbanization, Winter Crops 4200 cal yr BP event Late 3900 3000 Migrations, Summer Crops (rice, millet) 3500 cal yr BP event 3100 cal yr BP event – After 3000 Writing and Artifacts not found What about the Harappa? Technologically advanced society Water shortages Climate change “The more you know 

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