Ryan Levinson
Quaternary Stratigraphy
Fall 2015
The Younger Dryas Recorded in California Speleothem’s
Introduction
Variations in Earth’s climate are recorded in the geologic record. The melting of the
Arctic ice sheet can have catastrophic effects to the human population. Recently, researchers
have developed climate models that suggest that when Arctic sea ice disappears, the jet stream
shifts north, moving precipitation away from California(SOURCE). The marine isotope record
shows that there are alternating warm and cool periods in Earth’s paleoclimate deduced from
oxygen isotope data reflecting changes in temperature derived from data from deep sea core
samples in timescales shorter than timescales shown by the Milankovitch(SOURCE). The source
of small scale variations in Earth’s climate is not fully understood. Decadal cycles such as, El
Nino/Southern Oscillation (ENSO), the Northern Annular Mode (NAM), and the meridional
overturning circulation (MOC), have large-scale influences and strong regional impacts around
the globe. Although the 18O model is the most widely accepted model, speleothems provide 18O
data that are more detailed and much higher resolution history of the region. Speleothems are
used to understand hydrological processes, paleoclimate, the connection between ocean
atmosphere and land, indicator for seismic activity. Speleothems are well-suited for paleoclimate
reconstruction because they form with annual laminations, can be accurately dated using
radiometric dating, are usually very pure and well preserved, contain multiple climate proxies
(18O, 13C, Mg/Ca, Sr/Ca, P/Ca).
Background
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Milankovitch cycles- The Milankovitch cycles refer to long term variations in orbit of the
Earth which result in changes in climate over a ~22ka, ~44ka and ~100ka interval.
Oxygen isotope curve
Decadal cycles
Indian Ocean Dipole
Jet stream
Oceanic circulation (thermohaline circulation)
Ice records
Previous Studies
The National Centers for Environmental Information provide free data sets to users interested in
paleoclimate. With only 2 studies conducted in California, and less than 10 in Western America,
there is a lot of work that can be done on this subject. The Younger Dryas was recorded in a
speleothem archived in the Oregon Caves in south western Oregon. This study indicates that the
climate of this region cooled synchronously with the Younger Dryas climatic change elsewhere
in the Northern Hemisphere and the 18O record analyzed in this study indicates a century-scale
temperature variability during the early Holocene (Vacco 2004). The 13C record archived in
this speleothem records a response of biomass over the cave through the last deglaciation.
Studies in other parts of the world record paleoclimate data with extremely high precision
and resolution.
Narritive
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Statement- This research will establish regional proxies related to the Younger Dryas and
record the effects of El Nino during this period with decadal scale resolution.
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Objectives- The use of isotopic ratios, trace elements, and petrologic study to interpret
regional climatic variations.
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Significance- Apply interpretations associated with the onset of the Younger Dryas to
current climate models.
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Long Term Goals- Monitor isotopic ratios of water.
Science Plan
The Younger Dryas is one of the most well-known examples of abrupt climate change.
From ~13ka to ~12ka, temperature proxies show a decline of 2-6 degrees Celcius over most of
the northern hemisphere that resulted in advances of glaciers and drier conditions. The decline in
strength of the Atlantic meridional overturning circulation could have influenced rapid climate
change. Complex and variable effects of the Younger Dryas are recorded in the geologic record.
Hypothesis:
Although glacial and interglacial influence the Earth globally, regional variations do
occur. Analyzing the chemical composition, isotopic ratio’s, trace elements, petrography and
growth intervals can provide a record of regional paleoclimate variability. Although the cause of
Earth’s most recent stadial is still under debate, it appears that the thermohaline circulation, jet
stream and other factors may have influenced this sudden change in temperature. Interglacial
conditions were established before the Younger Dryas occurred. The addition of fresh water to
the Atlantic ocean due to the melting of the Greenland ice sheet may have caused the
thermohaline circulation to weaken, resulting in a dramatic decrease of temperature in the
northern hemisphere within a few decades. Applying this model to what is happening during
present times can be beneficial to society due to Earth’s steadily increasing population and
similar climatic conditions that preceded the onset of the Younger Dryas. Topics that this
research will focus on will (1) look for evidence recorded in speleothems that provide regional
paleo climatic information relating to the onset of the Younger Dryas in the Sierra Nevada and
Cascade mountain ranges, and (2) consider how decadal cycles such as El Nino effect the
regional climate during the Younger Dryas.
Program Description
The full potential of speleothem-based research has come to realization only during the
last decade. High quality research has been done using state of the art sampling (laser ablation
mass spectrometry), and dating (multi collector ICPMS) techniques. Commonly studied
speleothem-based paleoclimate proxies are:
1. Growth intervals: Determined by Uranium-series age determinations and used to identify
wetter vs. drier or warmer vs. cooler climate intervals (e.g., Ayliffe et al., 1998; Spötl et al.,
2002)The most commonly used methods for dating speleothems are Uranium-series dating.
Urainum-series dating is based on the decay of the parent isotopes 238U,234U to 230 Th. Age
uncertainties are associated with the presence of “initial” 230 Th, which is incorporated with
other impurities at the time of speleothem formation. Hiatuses and/or non –linear growth rates
can introduce chronological error into speleothem proxy records.
2. Oxygen (18O) isotope ratio: Interpreted as variations in cave temperature and properties of
rainfall (temperature, air mass trajectory, source and amount effects etc.)(McDermott et al.,
2004).18O of speleothem calcite is currently the most frequently used speleothem-based proxy
as it can provide information on 18O of precipitation on time scales ranging from annual to
millennial.
3. Carbon (13C) isotope ratio: Interpreted as changes in overlying vegetation (C3 versus C4
plants) and vegetation density (Dorale et al., 1998; Baldini et al., 2008). The potential corruption
of this signal downstream of the source caused by equilibration of aqueous CO2 with cave air is
also recognised, and in some cases, exploited as a proxy.numerous studies on stalagmites from
areas with different climatic settings suggest that 13C often reflects the degree of biogenic
activity above the cave and/or the ratio of C3 (trees and shrubs) to C4 (drought adapted grasses)
vegetation. Generally, higher biogenic activity and/or higher proportion of C3 vegetation (higher
precipitation) results in more negative 13C calcite values.
4. Annual band thickness: Used as a proxy for the amount of rainfall or mean annual temperature
(Polyak et al., 2001; Fleitmann et al., 2004) (Frisia et al., 2003; Tan et al., 2003). Annual laminae
(whose thickness typically varies between 50 and 500 μm) are in most cases the result of a strong
seasonality in the amount of surface precipitation and drip water supply. The thickness of annual
laminae can relate either to the amount of surface rainfall (e.g.,Polyak and Asmeron, 2001) or
cave air temperature (e.g., Tan et. al., 2003).
5. Trace elements: Interpreted as proxies for rainfall, vegetation, and growth rate and
increasingly measured at high resolution to resolve seasonal information and annual features
(e.g., Treble et al., 2003; Johnson et al., 2006). By using laser ablation inductively coupled
plasma mass spectrometry, trace elements such as Mg, P, U, Sr, Ba and Na can be measured at
sub-annual resolution. Recently published studies performed on speleothems from different
environmental settings reveal that both hydrological (e.g., amount of precipitation, groundwater
residence time, rock-water interaction) and/or growth-related processes can affect trace element
concentrations (e.g., Treble et al., 2003).
Test Hypothesis:
Uranium-series age determinations, isotopic ratios and trace element data can be used to
improve our understanding of paleo-hydrological, paleo-climatic, paleo-seismic, and many other
processes related to the regional geology. Uranium- series age determinations will be used as an
age control to determine the growth intervals within a speleothem. Isotopic ratios of 18O and
13C can provide information related to the properties of rainfall and the change in overlying
vegetation respectively. When measured precisely, trace element data can be used as a proxy to
study seasonal information and annual features. Collectively, age determinations and the 18O
ratios archived in the speleothems can be compared with the marine oxygen isotope graph to
examine regional variations in climate. Uranium series age determinations will be calculated
using…(what instruments are used to calculate ages… Mass Spectrometer?). Isotopic ratios will
be measured on a decadal scale by a Mass Spectrometer at Oregon State University. Trace
elements will be analyzed on a decadal scale using a laser plasma spectrometer. Age
determinations, isotopic ratios and trace element abundance measured on a decadal scale can
produce a high resolution regional paleo-climatic history.
Broader Impacts
Educating the next generation of scientists is an important part of my research. I believe
that my role as a scientist is to maintain a level of curiosity that keeps me detailed orientated and
determined to learn while influencing others to do the same. Maintaining a level of integrity that
allows the progression of science based on the scientific method. In previous years, I worked
with students enrolled in an afterschool program that was created to enrich and supplement
concepts learned in the classroom. During my time there, I was inspired to pursue science and
education. One of my goals in life is to scientifically educate people interested in pursuing
research in an area they are interested in. Field based research has been an important part in my
scientific career. Exposing others to field based observations, sample collection, and other
activities will enable people to spend time in nature, which has been proven to positively affect
people’s lives. Creating a program designed to expose students to academic projects of various
focuses will inspire future scientists to pursue a career in science. Encouraging students to
collaborate on an academic project will provide a foundation that can be used throughout their
lives. Young students often possess the curiosity and determination to become a good scientist.
My goal is to encourage students to develop their own ideas and prove them with science.
Justification
As climate change continues to effect food security, monitoring and reporting the effects
of climate conditions on food shortages worldwide becomes increasingly more important. Due to
the relatively sudden change in Earth’s climate, hypothesized to have taken place on a human
timescale, this is a serious topic that can potentially happen in the future. Today, melting glaciers
in Greenland and the Arctic are discharging freshwater into the Atlantic Ocean. Scientists believe
that when large amounts of freshwater is added to the Atlantic Ocean, the thermohaline
circulation changes. This change in the thermohaline circulation results in less heat being
transferred from equatorial regions to the northern hemisphere, resulting in abrupt climate
change and colder temperatures in the northern hemisphere. Since most of the land mass is in the
northern hemisphere, people will be dramatically effected by a global change of this magnitude.
Studying paleo-climatic patterns can provide insight to the probability of future events. The
Younger Dryas was studied because it was the most recent and longest of the several
interruptions to the gradual warming of Earth’s climate since the last glacial maximum.
Biographical sketch
Ryan C. Levinson, Undergraduate
(818) 723-4983 ryanlevinson13@gmail.com
1525 10th Street Arcata, CA 95521
Education
Undergraduate Humboldt State University, Arcata CA
December 2015 - Present
Humboldt State University Geology Program
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Interests: paleoclimate, oceanography, atmospheric science, igneous and sedimentary
petrology.
Prospective thesis: High Precision Investigation of Speleothems as a Proxy for Localized
Paleoclimate
Advisor: Dr. Brandon Browne
Professional Experience
Humboldt State University, Arcata CA
December 2015 - Present
Professor Assistant in the Department of Geology
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Assist undergrad petrology students with field study activities
Learning Enrichment Academic Program
September 2013 - June 2014
Program Director
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Develop comprehensive activities and exercises to improve student retention
Manage off campus education programs
Offer computer, writing, science lessons, music and physical education activities
to motivate students.
Owner: John Livings