Post by jonsdigs on Dec 5, 2006 0:22:30 GMT -5
Measuring past climate data: Part II
Nobel Intent
November 21, 2006 @ 7:51AM - posted by Chris Lee
The previous article focused on what might be thought of as biological measures of the global climate. In this article we take a look at other data sources that are not stored in biological tissue. This does not mean that the data is entirely free from biological influences, but the data interpretation is rendered a good deal simpler by the more subtle influences of life in these data sources.
Speleothems
Climatological data obtained from speleothems—stalactites and stalagmites—are a valuable resource as well. Like sedimentary layers, these growths contain information from multiple sources that can be used to analyze climatic conditions. Carried in with the water are pollen grains, organic acids, and trace elements, which all contains clues about the biological activity on the surface. In addition, speleothems grow in layers, which help date any findings, and the layer growth rates are also indicative of general climatic conditions as they reflect rain fall, humidity, and temperature. One of the attractions of data obtained from caves, ironically enough, is that they are relatively isolated from the immediate environment. Cave temperature and humidity can be well isolated from the daily external fluctuations and tends to reflect seasonal average conditions, though with an obvious offset—the temperature is lower and the humidity is higher. Further, the mineral precipitation that contributes to speleothem growth is not of biological origin and lacks the isotope biases that are prevalent in biological processes. Instead, it simply reflects the isotope ratios of the water modulated by the local temperature and relative humidity. This makes isotope ratios an especially attractive proxy for climate data derived from speleothems.
Isotope data is mainly measured in calcite and interpretation requires a thorough understanding of the cave system so that the fractionation of the water as it flows from the surface rain and into the cave system can be accounted for. In the case of simple, shallow cave systems, this is no more difficult than accounting for the hydrology of a lake catchment system. However, in complicated cave systems this can become a source of great uncertainty. Here, the detritus (e.g., pollen) included in the speleothem can be of help in identifying water sources. This, along with evidence that the speleothem stopped growing or changed axis slightly, can be used to gauge how ancient water flow compared to modern water flow. These difficulties in interpretation have limited the role of speleothem data to providing high resolution data that works in conjunction with better understood records, such as ice core records. The exceptions to this are in cave systems where the water flow is very well understood, such as those in Southern Oman.
Full Article
Nobel Intent
November 21, 2006 @ 7:51AM - posted by Chris Lee
The previous article focused on what might be thought of as biological measures of the global climate. In this article we take a look at other data sources that are not stored in biological tissue. This does not mean that the data is entirely free from biological influences, but the data interpretation is rendered a good deal simpler by the more subtle influences of life in these data sources.
Speleothems
Climatological data obtained from speleothems—stalactites and stalagmites—are a valuable resource as well. Like sedimentary layers, these growths contain information from multiple sources that can be used to analyze climatic conditions. Carried in with the water are pollen grains, organic acids, and trace elements, which all contains clues about the biological activity on the surface. In addition, speleothems grow in layers, which help date any findings, and the layer growth rates are also indicative of general climatic conditions as they reflect rain fall, humidity, and temperature. One of the attractions of data obtained from caves, ironically enough, is that they are relatively isolated from the immediate environment. Cave temperature and humidity can be well isolated from the daily external fluctuations and tends to reflect seasonal average conditions, though with an obvious offset—the temperature is lower and the humidity is higher. Further, the mineral precipitation that contributes to speleothem growth is not of biological origin and lacks the isotope biases that are prevalent in biological processes. Instead, it simply reflects the isotope ratios of the water modulated by the local temperature and relative humidity. This makes isotope ratios an especially attractive proxy for climate data derived from speleothems.
Isotope data is mainly measured in calcite and interpretation requires a thorough understanding of the cave system so that the fractionation of the water as it flows from the surface rain and into the cave system can be accounted for. In the case of simple, shallow cave systems, this is no more difficult than accounting for the hydrology of a lake catchment system. However, in complicated cave systems this can become a source of great uncertainty. Here, the detritus (e.g., pollen) included in the speleothem can be of help in identifying water sources. This, along with evidence that the speleothem stopped growing or changed axis slightly, can be used to gauge how ancient water flow compared to modern water flow. These difficulties in interpretation have limited the role of speleothem data to providing high resolution data that works in conjunction with better understood records, such as ice core records. The exceptions to this are in cave systems where the water flow is very well understood, such as those in Southern Oman.
Full Article