How Palaeoclimate data retrive from Ocean sediments and Ice core?

Question

This week I had lecture on Palaeo climate data. I am not clear about how the data recovered from stratigraphy methods or other methods? I searched on web but i found discussion about reuslts not about mehtods. I want to know the methods to retrive data and how to relate thes data with climate? Could you describes these methods.
Thank you.

Answer 1

Wow! An actual scientific question in Y!A Global Warming!

There are many methodologies for collecting, analyzing, and correlating the data from ocean sediments and ice cores. First, samples have to be obtained, which can be done with core drilling equipment. Then, the data are collected from the cores using any of a variety of physical/chemical techniques, depending on the type of data to be collected. The link below describes several such techniques. However, it should be understood that the characteristics of the sample from which the data are obtained tend to have originally been rather imprecise and, moreover, subject to change (e.g., diffusion) over the intervening time. Thus, it is something of an overstatement to say "By examining the trapped air we are able to work out precisely what the atmospheric composition was at the time the snow fell." Rather, it is useful to apply a variety of techniques to obtain various types of data, which can then be correlated to one another to help reduce the uncertainty.

Answer 2

Ice cores are normally extracted using a hollow drill, the cutting head is housed within a barrel and the whole apparatus is surrounded by a metal cylinder. Pressure is applied to the rotating head and it cuts down and around the core. The depth of the cut is determined by the length of the drill barrel, usually between 4 and 6 metres with 6 metres being the norm. When the maximum cutting length has been reached the whole assembly is raised to the surface and the ice removed from the core barrel.

Ice has a certain plasticity to it and thus the walls of the core hole deform under pressure. When the core reaches a certain depth (I would guess at about 250 metres) there is the risk that the hole will deform and to compensate for the back pressure a liquid hydrocarbon is used to fill the hole.

When the ice core is extracted it is cleaned, wrapped and storted for later analysis and the assemly lowered and the process begins again.

The ice caps are formed over thousands of years and are nothing more than compressed layers of snow that over time has built up layer by layer. Looking at an ice core sample is similar to looking at tree rings with demarkations showing the annual build up of snow. When snow falls it is ‘light and fluffy’ and traps air within it, over time the snow is compressed into ice through gravity and under pressure from subsequent snowfall, some of the aire remains trapped in the ice.

By examining the trapped air we are able to work out precisely what the atmosphereic composition was at the time the snow fell, this can be done for each year’s snowfall and over time builds to provide a historical record of atmopsheric composition. This process enables us to reconstruct the atmopshere over a period now approaching one million years. Ice core samples are taken at many sites around the world and thus emerges a global picture stretching far back into history.

Geological stratigraphy follows similar principles although a more powerful drilling process is required, with sedimentary stratigraphy a less powerful method is used and in many cases it’s simply direct pressure (no drilling as such, just pushing down into the sediment).

Different methods are employed to examine the cores and one of the most widely used is oxygen isotope analysis (oxygen 18). The analysis provides what is sometimes referred to as the isotopic signature.

Oxygen 18 is heavier than the ‘normal’ oxygen 16 and therefore evapourates less readily. The ratio between oxygen 16 and 18 laid down in the core record is examined and this provides a chronological record of the temperature and salinity of the water, this comes about because vapour tension is dependent on the concentration of salts dissolved in the water.

In sedimentary rocks, most notably limestone, chalk and other calcium carbonate rocks, the same principle applies. The different isotopes of oxygen are absorbed by animals and retained within the shells of CaCO3 secreting organisms. Because multicellular organisms have existed on the planet for 542 million years we are able to reconstruct the climatic record using O18 isotope analysis far back in time.

This is a very short answer and only addresses some of the aspects, there's a lot more to it than I've mentioned. If you need more info please add more details.