Week (10/6/2009) Summary
Topic: High latitude ice core records of past climate
Papers Discussed:
Barnola, J. M., D. Raynaud, Y. S. Korotkevich, and C. Lorius, 1987. Vostok ice core provides
160,000 - year record of atmospheric CO2. Nature, v. 329, p. 408 - 413.
Petit, J.R., et al., 1999. Climate and atmospheric history of the past 420,000 years from the
Vostok ice core, Antarctica. Nature, v. 399, p. 429-436.
EPICA community members, 2004. Eight glacial cycles from an Antarctic ice core, Nature, v.
429, p. 623-628.
North Greenland Ice Core Project members (NGRIP), 2004. High-resolution record of Northern
Hemisphere climate extending into the last interglacial period. Nature, v. 431, p. 147-151.
This week discussion focused on the analysis of ice core data from Antarctica and Greenland.
The importance of ice cores is that they provide a “snapshot” of past atmospheric conditions. Air is
trapped in the pore space of newly formed ice. After the pore closes, the gas remains stored in the ice.
By exposing the gases released from ice, certain climate and atmospheric indicators, such as carbon
dioxide and methane, can be analyzed.
Barnola et al. 1987 in “Vostok ice core provides 160,000 year record of atmospheric CO2”,
examined a 2083 meter long ice core drilled the Vostok region in East Antarctica. Measurements of
atmospheric CO2 were used to reconstruct previous atmospheric conditions of major climate events,
including the Holocene, the last glaciation, the previous interglacial, and the end of the penultimate
interglacial (Barnola et.al 1987). The results indicates that the CO2 cycle is cyclical and that the
interaction between climate and CO2 is dependent on whether there is a shift from glacial to interglacial
or from interglacial to glacial. This correlates with data from other sources, such as ice records from
Greenland and Antarctica, as well as deep sea sediment examinations of 13C of planktonic and benthic
foraminifera. Barnola et al concluded that there is a direct relationship between the influx of CO2 and
ocean circulation and its subsequent affect on Antarctica’s climate. Understanding how CO2 originating
from deep ocean water and CO2 originating from surface ocean water is crucial in understanding how the
earth climate could possibly respond to the current amount of CO2 in the atmosphere.
Petit et al. 1999 in “Climate and atmospheric history of the past 420,000 years from the Vostok
ice core, Antarctica” examined a 3623 meter long ice core drilled in the Vostok region. The data from the
ice core recorded approximately 420 kyr of climate and atmospheric history, covering four climate cycles.
Deuterium content of ice (D), dust, sodium (Na), 18Oatm, CO2 and methane (CO4) were examined.
Analysis led to the conclusion that glacial/interglacial cycles followed this pattern; temperature and
atmospheric concentrations of CO2 and CH4 rose steadily as the amount of dust decreased. Typically, this
indicates that the area was getting warmer and wetter. During the last half of the temperature rise, there
was a rapid increase of CH4, which coincided with the start of 18Oatm (temperature) decrease, potentially
starting a glacial period (Petit et al. 1999). Orbital forcing occurs, followed by an increased of CO2 and
CH4, which then led to deglaciation and ice-albedo feedback as the interglacial period begins (Petit et al.
1999). Similar to the other Vostok core, Petit et al emphasize the relationship of how atmospheric CO2
directly impact Antarctica’s climate. The results from the study provide another angle of how increased
levels of greenhouse gases are important in determining the future of Earth’s climate.
EPICA (The European Project for Ice Coring in Antarctica) Community Members 2004 in “Eight
glacial cycles from an Antarctic ice core” were able to excavate an ice core in Dome C, Antarctica, to
depths of 3190 meters, which has yielded approximately 740 kyr of atmospheric and climate data. It has
been determined that the core spans 8 glacial cycles. Conductivity, grain size, dust, and deuterium
content of ice CO2 and CH4, were examined. The data suggest that the past four glacial cycles (430 kyr to
present) supports the ice core data provided by the Vostok ice cores. For example, both Dome C and
Vostok cores observed the same pattern at Termination V, whose peak in D and CO2 are similar,
followed by an increase of both (EPICA 2004). The other four glacial cycles was (740 kyr-430 kyr) nonpronounce interglacial periods in Antarctica, but the higher proportion on each cycle were warmer
compared to the past four glacial cycles. MIS (Marine Isotope Storage) 11 is an interglacial period which
occurred approximately 430 kyr that is possibly analogous of current and/or future climate without human
intervention due to its similarities in length, low eccentricity, and weak processional forcing (EPICA
2004).
NGICP (North Greenland Ice Core Project) Project Members 2004 in “High resolution record of
Northern Hemisphere climate extending into the last interglacial period” drilled an ice core in Greenland
to attempt to reconstruct climate and atmospheric conditions of the Northern Hemisphere. NGRIP were
able to provide approximately 123 kyr of data covering the late Eemain and the last interglacial. 18O,
CH4, CO2, and N were analyzed. The data was compared to two other ice cores (GRIP and GISP2) that
were drilled previously and are located in the vicinity of NGICP. Comparative analysis was conducted on
the Vostok Ice cores and Iberian Margin sediment cores as well. NGICP showed similar 18O signatures
as both the Vostok and Iberian cores. However, the 18O data from NGRIP and GRIP did not correlate.
For example, the temperature of the NGICP during the Last Glacial Maximum was several degrees colder
than NGRIP and GISP2 (NGICP 2004). It is suggested by the authors that there may have been two
different air masses reaching the two sites. NGRIP was further from the ocean and may have seen a
higher fraction of air coming over the northern side of the Laurentide ice sheet, bringing with it colder,
more isotopically depleted moisture than what the GRIP may have seen (NGCIP 2004).
The four articles are examples of how ice core data is being used to reconstruct the atmospheric
and climate conditions of earth’s recent history. Finding areas that meet specific guidelines, such as
minimum ice flow deformation, flat bedrock, low precipitation rate, and area’s high enough in elevation
are difficult, thus limiting the usefulness of this procedure globally. Climate and atmospheric conditions
in the Northern and Southern hemisphere differ and more advance models are needed to reconcile those
differences. More importantly, understanding Earth’s climatic response to elevated greenhouse gases in
the past is crucial to understand the Earths future climate.