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The article needed to answer the questions is attached. Here are the questions below……. 1. Using evidence from the text, explain the meaning of “yrBP” on the lower x axis? 2. Using evidence from the text, compare, and contrast the way the X and y axis’s are implemented? 3. Which of the variables graphed appears most linked to temperature changes? Explain using answers from the text. 4. Which of the variables graphed appears least linked to temperature changes? Explain using answers from the text.. 5.Compare and contrast the evidence of earths history found in rock layers verse ice cores? Support your response by using evidence from the text. Here is the text link I also attached as a pdf
Ice core basics
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Ice core basics
Why use ice cores? | How do ice cores work? | Layers in the ice | Information from ice cores | Further
reading | References | Comments |
Why use ice cores?
420,000 years of ice core data from Vostok,
Antarctica research station. Current period is
at right. From bottom to top: * Solar
variation at 65°N due to en:Milankovitch
cycles (connected to 18O). * 18O isotope of
oxygen. * Levels of methane (CH4). *
Relative temperature. * Levels of carbon
dioxide (CO2). From top to bottom: * Levels
of carbon dioxide (CO2). * Relative
temperature. * Levels of methane (CH4). *
18O isotope of oxygen. * Solar variation at
65°N due to en:Milankovitch cycles
(connected to 18O). Wikimedia Commons.
Ice sheets have one particularly special property. They allow us to go back in time and to sample
accumulation, air temperature and air chemistry from another time[1]. Ice core records allow us to
generate continuous reconstructions of past climate, going back at least 800,000 years[2]. By looking
at past concentrations of greenhouse gasses in layers in ice cores, scientists can calculate how
modern amounts of carbon dioxide and methane compare to those of the past, and, essentially,
compare past concentrations of greenhouse gasses to temperature.
Ice coring has been around since the 1950s. Ice cores have been drilled in ice sheets worldwide, but
notably in Greenland[3] and Antarctica[4, 5]. High rates of snow accumulation provide excellent time
resolution, and bubbles in the ice core preserve actual samples of the world’s ancient atmosphere[6].
Through analysis of ice cores, scientists learn about glacial-interglacial cycles, changing atmospheric
carbon dioxide levels, and climate stability over the last 10,000 years. Many ice cores have been
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Ice core basics
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drilled in Antarctica.
Antarctic ice core drill sites with depth and record duration. From the US ITASE project.
This photograph shows an ice core sample being taken from a drill. Photo by Lonnie Thompson, Byrd Polar
Research Centre, Ohio State University. From Wikimedia Commons.
This picture shows a traversing field camp from December 2010. The team were travelling across the West
Antarctic Ice Sheet to study snow accumulation. They spent two nights at each site, first collecting radar data
and secondly collecting a 15 m shallow ice core. From Wikimedia Commons.
How do ice cores work?
This schematic cross section of an ice sheet
shows an ideal drilling site at the centre of
the polar plateau near the ice divide, with
ice flowing away from the ice divide in all
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direction. From: Snowball Earth.
The large Greenland and Antarctic ice sheets have huge, high plateaux where snow accumulates in
an ordered fashion. Slow ice flow at the centre of these ice sheets (near the ice divide) means that
the stratigraphy of the snow and ice is preserved. Drilling a vertical hole through this ice involves a
serious effort involving many scientists and technicians, and usually involves a static field camp for a
prolonged period of time.
Shallow ice cores (100-200 m long) are easier to collect and can cover up to a few hundred years of
accumulation, depending on accumulation rates. Deeper cores require more equipment, and the
borehole must be filled with drill fluid to keep it open. The drill fluid used is normally a petroleumderived liquid like kerosene. It must have a suitable freezing point and viscosity. Collecting the
deepest ice cores (up to 3000 m) requires a (semi)permanent scientific camp and a long, multi-year
campaign[6].
Layers in the ice
If we want to reconstruct past air temperatures, one of the most critical parameters is the age of the
ice being analysed. Fortunately, ice cores preserve annual layers, making it simple to date the ice.
Seasonal differences in the snow properties create layers – just like rings in trees. Unfortunately,
annual layers become harder to see deeper in the ice core. Other ways of dating ice cores include
geochemisty, layers of ash (tephra), electrical conductivity, and using numerical flow models to
understand age-depth relationships.
This 19 cm long of GISP2 ice core from 1855
m depth shows annual layers in the ice. This
section contains 11 annual layers with
summer layers (arrowed) sandwiched
between darker winter layers. From the US
National Oceanic and Atmospheric
Administration, Wikimedia Commons.
Although radiometric dating of ice cores has been difficult, Uranium has been used to date the Dome
C ice core from Antarctica. Dust is present in ice cores, and it contains Uranium. The decay of 238U to
234
U from dust in the ice matrix can be used to provide an additional core chronology[7].
Information from ice cores
Accumulation rate
The thickness of the annual layers in ice cores can be used to derive a precipitation rate (after
correcting for thinning by glacier flow). Past precipitation rates are an important palaeoenvironmental
indicator, often correlated to climate change, and it’s an essential parameter for many past climate
studies or numerical glacier simulations.
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Melt layers
Ice cores provide us with lots of information beyond bubbles of gas in the ice. For example, melt
layers are related to summer temperatures. More melt layers indicate warmer summer air
temperatures. Melt layers are formed when the surface snow melts, releasing water to percolate
down through the snow pack. They form bubble-free ice layers, visible in the ice core. The distribution
of melt layers through time is a function of the past climate, and has been used, for example, to show
increased melting in the Twentieth Century around the NE Antarctic Peninsula[8].
Past air temperatures
It is possible to discern past air temperatures from ice cores. This can be related directly to
concentrations of carbon dioxide, methane and other greenhouse gasses preserved in the ice. Snow
precipitation over Antarctica is made mostly of H216O molecules (99.7%). There are also rarer stable
isotopes: H218O (0.2%) and HD16O (0.03%) (D is Deuterium, or 2H)[9]. Isotopic concentrations are
expressed in per mil δ units (δD and δ18O) with respect to Vienna Standard Mean Ocean Water (VSMOW). Past precipitation can be used to reconstruct past palaeoclimatic temperatures. δD and δ18O
is related to surface temperature at middle and high latitudes. The relationship is consistent and
linear over Antarctica[9].
Snow falls over Antarctica and is slowly converted to ice. Stable isotopes of oxygen (Oxygen [16O, 18O]
and hydrogen [D/H]) are trapped in the ice in ice cores. The stable isotopes are measured in ice
through a mass spectrometer. Measuring changing concentrations of δD and δ18O through time in
layers through an ice core provides a detailed record of temperature change, going back hundreds of
thousands of years.
The figure above shows changes in ice
temperature during the last several glacialinterglacial cycles and comparison to
changes in global ice volume. The local
temperature changes are from two sites in
Antarctica and are derived from deuterium
isotopic measurements. The bottom plot
shows global ice volume derived from δ18O
measurements on marine microfossils
(benthic foraminifera) from a composite of
globally distributed marine sediment cores.
From Wikimedia Commons.
An example of using stable isotopes to reconstruct past air temperatures is a shallow ice core drilled
in East Antarctica[10]. The presence of a “Little Ice Age”, a cooler period ending ~100 to 150 years
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ago, is contested in Antarctica. Disparate records often provide conflicting evidence. This ice core
attempted to investigate the evidence for cooler temperatures during this period.
A 180 m deep ice core from the Ross Sea, Antarctica, was drilled by a team led by Nancy Bertler in
2001/2002[10]. The top 50 m of the ice core was analysed at 2.5 cm resolution using a continuous
melting system. Ice core samples were analysed for stable isotope ratios, major ions and trace
elements. An age model was extrapolated to the ice core using a firm decompaction model[10].
Deuterium data (δD) were used to reconstruct changes in summer temperature in the McMurdo Dry
Valleys over the last 900 years. The study showed that there were three distinct periods: the Medieval
Warm Period (1140 to 1287 AD), the Little Ice Age (1288 to 1807 AD) and the Modern Era (1808 to
2000 AD).
These data indicate that surface temperatures were around 2°C cooler during the Little Ice Age[10],
with colder sea surface temperatures and possibly increased sea ice extent, stronger katabatic winds
and decreased snow accumulation. The area was cooler and stormier.
Past greenhouse gasses
This photograph shows me (Bethan Davies)
visiting Nancy Bertler and others in her ice
core laboratory at GNS, New Zealand. The
ice core is continuously melted and analysed
by numerous automatic machines.
The most important property of ice cores is that they are a direct archive of past atmospheric gasses.
Air is trapped at the base of the firn layer, and when the compacted snow turns to ice, the air is
trapped in bubbles. This transition normally occurs 50-100 m below the surface[6]. The offset
between the age of the air and the age of the ice is accounted for with well-understood models of firn
densification and gas trapping. The air bubbles are extracted by melting, crushing or grating the ice in
a vacuum.
This method provides detailed records of carbon dioxide, methane and nitrous oxide going back over
650,000 years[6]. Ice core records globally agree on these levels, and they match instrumented
measurements from the 1950s onwards, confirming their reliability. Carbon dioxide measurements
from older ice in Greenland is less reliable, as meltwater layers have elevated carbon dioxide (CO2 is
highly soluble in water). Older records of carbon dioxide are therefore best taken from Antarctic ice
cores.
Other complexities in ice core science include thermal diffusion. Prior to becoming trapped in ice, air
diffuses to the surface and back. There are two important fractionation processes: thermal diffusion
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and gravitational settling[11]. Thermal diffusion occurs if the surface is warmer or colder than the
bottom boundary (the close-off depth). This temperature gradient occurs from climate change, which
affects the surface first. The heavier components of the air (like stable isotopes) also tend to settle
down (gravitational settling).
Thermal diffusion and gravitational settling can be measured and analysed because the fractionation
of air follows well understood principles and relationships between different stable isotopes (namely,
nitrogen and argon).
Other gasses
Other major gases trapped in ice cores (O2, N2 and Ar) are also interesting. The stable isotope
concentration (δ18O) in ice core records mirrors that of the ocean. Oceanic δ18O is related to global ice
volume. Variations of δ18O in O2 in ice core gasses are constant globally, making it a useful
chronostratigraphic marker. It’s another way to relate ice-core chronologies.
Other ice-core uses
The vertical profile of an ice core gives information on the past surface temperature at that
location[6]. In Greenland, glass shard layers from volcanic eruptions (tephra) are preserved in ice
cores. The tephra ejected in each volcanic eruption has a unique geochemical signature, and large
eruptions projecting tephra high into the atmosphere results in a very wide distribution of ash. These
tephra layers are therefore independent maker horizons; geochemically identical tephra in two
different ice cores indicate a time-synchronous event. They both relate to a single volcanic eruption.
Tephra is therefore essential for correlating between ice cores, peat bogs, marine sediment cores,
and anywhere else where tephra is preserved[12, 13].
Changes in sea ice concentrations can also be reconstructed from polar ice cores[14]. Ice core records
of sea salt concentration reveal patterns of sea ice extent over longer (glacial-interglacial) timescales.
Methane sulphonic acid in near-coastal ice cores can be used to reconstruct changes and interannual
variability in ice cores.
Mineral dust accumulates in ice cores, and changing concentrations of dust and the source
(provenance) of the dust can be used to estimate changes in atmospheric circulation[15]. The two
EPICA ice cores (European Project for Ice Coring in Antarctica) contain a mineral dust flux record,
showing dust emission changes from the dust source (glacial Patagonia). Changes in the dust
emission is related to environmental changes in Patagonia.
Further reading
IPICS (International Partnerships in Ice Core Sciences)
Ice cores and climate change (British Antarctic Survey)
NSIDC: Ice cores in Antarctica and Greenland
Ice core research at Victoria University of Wellington, New Zealand
James Ross Island ice core
References
1.
Jouzel, J. and V. Masson-Delmotte, 2010. Deep ice cores: the need for going back in time.
Quaternary Science Reviews, 29(27): 3683-3689.
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2.
Augustin, L., C. Barbante, P.R.F. Barnes, J.M. Barnola, M. Bigler, E. Castellano, O. Cattani, J.
Chappellaz, D. DahlJensen, B. Delmonte, G. Dreyfus, G. Durand, S. Falourd, H. Fischer, J. Fluckiger,
M.E. Hansson, P. Huybrechts, R. Jugie, S.J. Johnsen, J. Jouzel, P. Kaufmann, J. Kipfstuhl, F. Lambert, V.Y.
Lipenkov, G.V.C. Littot, A. Longinelli, R. Lorrain, V. Maggi, V. Masson-Delmotte, H. Miller, R. Mulvaney,
J. Oerlemans, H. Oerter, G. Orombelli, F. Parrenin, D.A. Peel, J.R. Petit, D. Raynaud, C. Ritz, U. Ruth, J.
Schwander, U. Siegenthaler, R. Souchez, B. Stauffer, J.P. Steffensen, B. Stenni, T.F. Stocker, I.E.
Tabacco, R. Udisti, R.S.W. van de Wal, M. van den Broeke, J. Weiss, F. Wilhelms, J.G. Winther, E.W.
Wolff, M. Zucchelli, and E.C. Members, 2004. Eight glacial cycles from an Antarctic ice core. Nature,
429(6992): 623-628.
3.
Johnsen, S.J., D. Dahl-Jensen, N. Gundestrup, J.P. Steffensen, H.B. Clausen, H. Miller, V.
Masson-Delmotte, A.E. Sveinbjornsdottir, and J. White, 2001. Oxygen isotope and palaeotemperature
records from six Greenland ice-core stations: Camp Century, Dye-3, GRIP, GISP2, Renland, and
NorthGRIP. Journal of Quaternary Science, 16: 299-307.
4.
Mulvaney, R., N.J. Abram, R.C.A. Hindmarsh, C. Arrowsmith, L. Fleet, J. Triest, L.C. Sime, O.
Alemany, and S. Foord, 2012. Recent Antarctic Peninsula warming relative to Holocene climate and
ice-shelf history. Nature, 489: 141-144.
5.
Lambert, F., B. Delmonte, J.-R. Petit, M. Bigler, P.R. Kaufmann, M.A. Hutterli, T.F. Stocker, U.
Ruth, J.r.P. Steffensen, and V. Maggi, 2008. Dust-climate couplings over the past 800,000 years from
the EPICA Dome C ice core. Nature, 452(7187): 616-619.
6.
Brook, E.J., ICE CORE METHODS | Overview, in Encyclopedia of Quaternary Science, A.E.
Scott, Editor. 2007, Elsevier: Oxford. 1145-1156.
7.
Aciego, S., B. Bourdon, J. Schwander, H. Baur, and A. Forieri, 2011. Toward a radiometric ice
clock: uranium ages of the Dome C ice core. Quaternary Science Reviews, 30(19): 2389-2397.
8.
Abram, N.J., R. Mulvaney, E.W. Wolff, J. Triest, S. Kipfstuhl, L.D. Trusel, F. Vimeux, L. Fleet,
and C. Arrowsmith, 2013. Acceleration of snow melt in an Antarctic Peninsula ice core during the
twentieth century. Nature Geosci, advance online publication.
9.
Jouzel, J. and V. Masson-Delmotte, ICE CORE RECORDS | Antarctic Stable Isotopes, in
Encyclopedia of Quaternary Science, A.E. Scott, Editor. 2007, Elsevier: Oxford. 1242-1250.
10.
Bertler, N.A.N., P.A. Mayewski, and L. Carter, 2011. Cold conditions in Antarctica during the
Little Ice Age – implications for abrupt climate change mechanisms. Earth and Planetary Science
Letters, 308: 41-51.
11.
Grachev, A.M., ICE CORE RECORDS | Thermal Diffusion Paleotemperature Records, in
Encyclopedia of Quaternary Science, A.E. Scott, Editor. 2007, Elsevier: Oxford. 1280-1284.
12.
Abbott, P.M. and S.M. Davies, 2012. Volcanism and the Greenland ice-cores: the tephra
record. Earth-Science Reviews, 115(3): 173-191.
13.
Hoek, W., Z. Yu, and J.J. Lowe, 2008. INTegration of Ice-core, MArine, and TErrestrial records
(INTIMATE): refining the record of the Last Glacial – Interglacial Transition. Quaternary Science
Reviews, 27(1): 1-5.
14.
Abram, N.J., E.W. Wolff, and M.A.J. Curran, 2013. A review of sea ice proxy information from
polar ice cores. Quaternary Science Reviews, 79(0): 168-183.
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15.
Fischer, H., F. Fundel, U. Ruth, B. Twarloh, A. Wegner, R. Udisti, S. Becagli, E. Castellano, A.
Morganti, and M. Severi, 2007. Reconstruction of millennial changes in dust emission, transport and
regional sea ice coverage using the deep EPICA ice cores from the Atlantic and Indian Ocean sector of
Antarctica. Earth and Planetary Science Letters, 260(1): 340-354.
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