Ice-Core Based Studies of Climate and Atmospheric Changes

Activity Rationale

The detailed history of polar temperatures, precipitation rates, and atmospheric composition are locked in ice caps. Ice-core studies have provided most of what we know about climate change over the last million years. By studying the range and behaviour of past natural changes in climate, we can begin to understand how the Earth’s climate system will respond to modern global change.

Leader: David Fisher

The Topic

Snow and ice cores preserve histories of temperature, precipitation, and atmospheric composition, providing a wealth of information about the evolution and variability of the Earth’s climate system. As ice sheets build up over time from the accumulation of snow and ice, the annual layers trap many clues about the climatic conditions that occurred when the ice was formed. Scientists use proxy evidence (such as stable isotopes, gasses, and salt content) within ice cores to infer histories of temperature, precipitation, atmospheric conditions, ocean volume, sea ice extent, volcanic eruptions, solar variability, extra terrestrial particles, and others.

Ice cores provide a strong basis for research because many climate indicators can be measured on the same core, and the processes that produce those indicators can be linked. Ice cores also provide very long records of climatic conditions (the longest record being 800,000 years), which is essential for gaining an understanding of the natural variability of the Earth’s climate.

The key variables (proxies) examined in ice cores and their meanings are listed in the table below.

Ice Core Variables and What they Say

Variable	Units	Proxy For	Topic Experts in GSC
Stable  Isotopes:    (D) and (18O) (D= deuterium, a hydrogen isotope)	0/00	Temperature, accumulation rate, and elevation at the deposition site; origin of source water; noise (data interference) from local re-working of snow and sastrugi noise.	D. Fisher C. Zdanowicz
Accumulation rate	m/year	Snow fall rate and density.	M. Demuth D. Fisher D. Burgess
Melt percent	%	Peak summer temperature at the site.	D. Fisher C. Zdanowicz M. Demuth D. Burgess
Bore  hole  temperatures	°C	Mean annual air temperature at the site (elevation of deposition point is a factor).	D. Fisher
Pollen	number/ litre	Pollen productivity at the source; storm intensity and directions.	J. Bourgeois P. Outridge
Salts	PPB (parts per billion) and mass	Sea ice extent; marine storminess; air temperature;     water vapour content.	C. Zdanowicz J. Zheng J. Sekerka
Acids	[H+]	Volcanic activity; marine biological productivity; recent human acid pollution.	J. Zheng D. Fisher J. Sekerka
Mineral dust	PPB	Distance to continental source areas; windiness and water vapour content over the whole cycle.	C. Zdanowicz D. Fisher J. Zheng M. Parnandi
Gases	PPB by volume (cm3/g)	Atmospheric composition (since gases mix quickly and homogeneously they should be the same in all ice cores, so they are used to cross-date distant ice cores).	D. Fisher J. Zheng
MSA	PPB	MSA (methane sulfonate) is a daughter product of DMS (dimethyl sulfide), which is related to marine surface water productivity of living planktonic algae. DMS is a precursor for CCN (cloud condensation nuclei), so MSA could be an indicator for CCN. CCN are the “seeds” that clouds form on, which reflect incoming solar radiation.	J. Zheng J. Bourgeois
Trace metals (lead, mercury, etc)	PPT (parts per trillion) by mass	Natural and anthropogenic concentrations of lead and mercury (among others) can be traced through time, documenting the history of metal mining, refining, and use. This provides essential information for monitoring potentially harmful additives to our environment.	J. Zheng P. Outridge

 

The Canadian ice coring effort has been lead by the Geological Survey of Canada (GSC) since 1970. The ice caps of the Canadian Arctic provide 100,000 years of data for many climate indicators, with detailed coverage of the last post-glacial period (roughly the last 12,000 years). Along with ice cores from Greenland, Antarctica, and other sites, ice cores from the Canadian Arctic have made important contributions to defining the Earth’s climate history.

Results

The Holocene period (beginning about 12,000 years ago) is characterized by the relatively warm “normal” climate during which humans have flourished. How stable was this period, and how did it change naturally over time? Studies on ice cores from Greenland and Canada have provided some insights.

The graphs below show comparisons of cores from Greenland and Ellesmere Island (North-eastern Canada). The cores show similarities and differences. The graphs (a-d) show the oxygen isotope records preserved in the ice cores during the Holocene. Oxygen isotopes are an important proxy indicator for temperature. The Agassiz (a) and Renland (c) records show very similar profiles, with a pronounced warm period in the early Holocene due to changes in the Earth’s orbit. During this time, the average temperature was about 3.5 °C warmer than present, and there was no sea ice left in the Arctic Ocean or between the Canadian Islands at this time. It is thought that the Agassiz and Renland records show the true temperature history and the records from central Greenland (b) show different trends because of significant elevation changes at these sites over the last 12,000 years.

From the graphs above, it appears that the climate has changed since the early Holocene due to natural insolation (solar radiation) changes indicated in (d). The temperature changes have been gradual; since the early Holocene when the average temperature was about 3.5 °C warmer than present, there has been a long, slow cooling trend before the abrupt warming in the last century.

The explanation of why these cores are so different lies in the location of the sample sites. Since Mt. Logan is located near the Pacific coast of Canada, it experiences different climatic conditions than the Atlantic cores in Greenland and Ellesmere Island. It is thought that the record for Mt. Logan reflects changes in the moisture flow from the tropics, which is driven by large changes in the strength of the El Niňo/La Niňa oscillation (ENSO) throughout the Holocene. 

One of the great changes recorded in the Mt. Logan record is a large drop in temperature (derived from the oxygen isotope record, O-18) around 4200 years ago (a). This event is consistent with a time in human history when a number of growing agricultural civilizations in various parts of the world came to an end (such as the Old Kingdom in Egypt and the Akkadian Empire in Mesopotamia). This was probably a reflection of a “mega-ENSO” event that suddenly altered climate in many parts of the world.

 

 

 

 

Study Data

The following glaciological ice core datasets are available from the (United States) National Climatic Data Center (NCDC):

• Agassiz Ice Cap (oxygen isotope, ECM, melt percent, accumulation)
• Devon Ice Cap (oxygen isotope, particle, conductivity, chemistry)
• Penny Ice Cap (conductivity, isotope, chemistry)
• Mt. Logan (7400 year glaciochemical data)

Links

Ice core data from the National Climatic Data Centre

Past research and results from Mt. Logan ice-core studies, Earth Sciences Sector

National Glaciology Group

Natural Elements article: Drilling Into the Past

History of Mt. Logan

Publications

Please note that subscriptions may be required to access some articles. To request a copy of publications, or for any more information, please contact David Fisher

• Check for more recent publications in GEOSCAN, the publications database of the Geological Survey of Canada and the Canada Centre for Remote Sensing.

Vinther, B.M., Clausen, H.B., Fisher, D.A., Koerner, R.M., Johnsen, S.J., Andersen, K.K., Dahl-Jensen, D., Rasmussen, S.O., Steffensen, J.P. and A.M. Svensson (2008). Synchronizing ice cores from the Renland and Agassiz ice caps to the Greenland ice core chronology. Journal of Geophysical Research, 113,D08115, doi:10.1029/2007JD009143,2008 :10 pages.

Fisher D.A., Osterberg, E., Dyke, A., DahlJensen, D., Demuth, M., Zdanowicz, C., Bourgeois, J. ,Koerner, R.M., Mayewski, P., Wake C., Kreutz K., Steig E., Zheng J., Yalcin K., Goto-Azuma K.,Luckman B. and S Rupper (2008). The Mt Logan Holocene-Lat Wisconsinian isotope record: tropical Pacific B Yukon connections. The Holocene, 18(5):667-677.

Fisher, D.A., Dyke, A., Koerner, R., Bourgeois, J., Kinnard, C., Zdanowicz, C., De Vernal, A., Hillaire-Marcel, C., Savele, J. and A. Rochon (2006). Natural variability of Arctic sea ice over the Holocene. Eos Transactions, AGU, 87(28):273-275.

Fisher D.A. and R.M. Koerner (2004). Holocene Ice Core Climate History, a Multi-Variable Approach. A chapter in a book Global Change in the Holocene. Arnold Press, London.