The variations in the continental ice shield and the amount of ice in the ocean strongly influence the development of below sea level deposits off the west coast of the Antarctic Peninsula, and this influences global climate.
It is possible to backtrack these variations over periods of several millions of years using core-depth drillings.
Particle size analysis significantly helps this. The particle distribution of the obtained material is known as a substantial parameter, which is determined during the examination of the sediments. The first extensive procedure here is a process where the share of a particle size smaller than 63 µm is obtained and then prepared for the particle size determination.
Figure 1. Preparation path for the examination of the fine share of sediment material
An ANALYSETTE 22 was used to analyze the obtained material, and the results were examined using different methods. Examples shown in this article are contour-plots of the fine share against the drilling depth and the age of the sediment. The share larger than 63 µm is shown in a separate column for each case.
The contour-plot of the particle size distribution is shown in Figure 2. The particle size distribution for the sample material from various drilling depths was divided into six size classes and then color-coded.
Figure 2A. Applied against the drilling depth in 1 m intervals.
Figure 2B. Applied against the obtained from magnetic measuring age of the sediments in steps of 20 years each. Recognizable are several intervals, in which the cyclicity and the relation of clay/silt vary.
The distribution momentums can be obtained from the measured distributions. These momentums are statistical values, which in a brief, concise form, characterize the distributions.
For example, the standard deviation of the distribution is a statistical value, which is a dimension for its width, or 'skewness.' This value reveals if a distribution is symmetrical (skewness = 0), featuring an increased amount of coarse area (skewness >0) or in the fine area (skewness <0).
Figure 3 shows how a number of these statistical parameters are applied, against the drilling depth and also against the age of the sediment. However, the fine share was smaller than 10 µm initially removed, since vital information with regard to deposit processes was delivered by the special share between 10 and 63 µm.
Figure 3. Moments of the distribution applied against depth, respectively age. Considered here is only the share of the sediment with grain sizes in the range of 10-63 µm.
When applying the obtained skewness of all measured distributions, firstly against the mean value of the particle size and secondly against the standard deviation of the distribution, it is clearly seen in this illustration that there are three populations which can be matched to various depositing processes of the sediments, (Figure 4).
Figure 4. Skewness of the distribution applied against the median value respectively the standard deviation of the distribution. Three different populations are clearly recognizable.
When the individual populations are observed, the diagrams shown in Figure 5 are obtained. These diagrams provide detailed conclusions about the chronological order of the depositing processes, which provide vital information about factors affecting these processes, including, for example, the median temperature.
Figure 5. Distribution of the single population applied over the drilling depth and the age of the sediments. Each population is colour coded and the amplitudes show the medium grain size. The black curves present the share of the respective population in 10 m intervals.
This information has been sourced, reviewed and adapted from materials provided by FRITSCH GMBH - Milling and Sizing.
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