Wikibooks: Historical Geology/Ice cores

• Format: Book
• Language: English
• Subjects: ice core
• Online Access: https://en.wikibooks.org/wiki/Historical_Geology/Ice_cores

In this article we shall look at how core samples from ice can be used to give us information about paleoclimates. The reader may find it useful to look back at [[the main article on glaciers]] before reading further. =Ice layers= At any location where snow falls but does not melt (or at least does not completely melt) before the next year s snowfall the snow will accumulate and as each year s snow is buried by the further snowfall of succeeding years it compacts from loose snow to permeable firn to impermeable ice at which point it is said to undergo closure . You should remember from [[the article on glaciers]] that any point at which snow accumulates like this must inevitably become the [[accumulation zone]] of a [[glacier]]. Ice formed from summer snow is lighter and less dense than ice formed from winter snow as a result if the rate of accumulation is more than about 4 cm/year we get what in effect are [[varves]] formed from snow. At least in the upper part of the [[glacier]] these are plainly visible if we take a core sample as you can see in the photograph below right. =Ice core data= The fact that the ice cores contain visible annual layers means that just as with varves in lakes we can count them down from the top and assign a year to each one. Looking at the thickness of each layer we can quantify the amount of snowfall or at least unmelted snowfall in the summer and winter of each year. What is perhaps more interesting we can measure the 16 O/ 18 O ratio of the water which acts as a climatic indicator for reasons discussed in [[the article on scleroclimatology]] we can also measure the 1 H/ 2 H ratio of the water which acts as a climatic indicator for the same reason water [[molecules]] containing the 2 H [[isotope]] are slightly heavier and so evaporate less readily. Besides these data when the permeable firn turns to impermeable ice bubbles of the atmosphere become trapped within the ice. This allows us to analyze the past composition of the atmosphere and quantify gasses which affect the ...