What gets incorporated/trapped into (sampled by) glacial ice?

• 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?
• shearing.

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 eruption.
  • 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 latitude.
• 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 change?

With what record can the ice sheet records be compared with in order to establish global patterns?

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:
  • OCCAM global ocean circulation model - fairly technical, but rich in information, and with some nice animations.
  • World Ocean Circulation Experiment Global Data Resource .
  • University of California at San Diego - virtual museum on global ocean circulation.

Discussion question: What drives thermohaline circulation (be as specific as possible), and list factors that determine its pattern.