Global Climate Change seminar -
Records in Ice
What gets incorporated/trapped into (sampled by) glacial
- water with its isotopic signature.
- gas, past samples of atmosphere.
- dust of various types: volcanic, oranic ash, desert dust.
- other atmospheric precipitates - e.g. sulfur compounds.
- cosmogenic isotopes.
- chemicals from marine algae (?).
- for each of these, think on what might control the amount
or character of that signal.
Process of snow to ice:
- melting and refreezing (especially in the summer): more in
summer -> larger grains. Production of annual couplets.
- compaction deeper down
- what is significance of compaction for above samples?
How are annual layers evident?
What is accuracy of layer counting?
- decreases as go back
- within 1 % for last 11,500 years for Greenland cores.
- how determined/tested?
- volcanic ash which can be dated, or correlated with known
- 10Be isotope accumulation, cosmogenic isotopes useful for
dating time since communicated with surface realm.
What is length of record they have from Greenland?
- up to 110,000 years
- double that from Antarctica
- records from Svalbard, from southern Andes, of shorter duration,
but important because of location.
From isotopic to temperature signatures:
- stable vs. unstable isotopes.
- starting point SMOW standard mean ocean water isotope values
(use diagram to depict).
- key to this is fractionation: when water evaporates
18O and deuterium are heavier and tend to stay in the seawater.
When it condenses to form precipitation, the opposite happens
and rain or snow is then enriched in 18O and D relative to the
atmospheric reservoir it came from.
- observed that degree of fractionation increase with geographic
- what determines the degree of fractionation?
- progressive fractionation history (as remove it then changes)
- temperature effect
- re-evaporation from surface water at higher latitude
What were results of analysis of Greenland cores?
What might be a particular important control for Greenland
and Antarctica, and how might that be related to global climate
With what record can the ice sheet records be compared with
in order to establish global patterns?
Small ice caps on Svalbard.
Next we will start to investigate what might be some of
the consequences of global warming?
Reading for next time:
- Broeker, W., 1997, Will our ride into the Greenhouse future
be a Smooth One? GSA Today, 7, # 5, 1-7.
- Please browse thorugh these and related links:
Discussion question: What drives thermohaline circulation
(be as specific as possible), and list factors that determine