Originally Posted by
SkyWriting
That part your just making up for dramatic effect.
All Righty Then:
The d18O records confirm that large and rapid temperature oscillations have occurred through most of the last 110,000 year period. They are of a scale that has not been experienced during the past 10,000 years in which human society mainly developed......
Especially astonishing are the very short times needed for major warmings. A temperature increase of 5C can occur in a few decades.
The d18O and d2H values of water vapour and water in air masses are depleted when moving to colder regions. In Greenland and in Antarctica a linear relationship between the delta values of an annual snow layer and the local mean annual surface temperature is observed.
This empirical linear relationship observed at present for locations with different surface temperature is the basis for reconstructing past temperature. The linear relationship can be explained qualitatively through simple Rayleigh type isotopic models, but there is no guarantee that exactly the same empirical relationship was valid in earlier climatic epochs. With the two ice cores from Summit, it is possible, for the first time, to make a kind of calibration of the delta records. Borehole temperatures lack the high time resolution of isotopic records, but they are relatively insensitive to any factors other than surface temperature at the time of snow deposition.
The idea of this calibration is not new but it can only be applied with accuracy when the transition from the last glaciation to the Holocene occurs far above bedrock. Two independent calibrations, using separate data sets and different techniques, agree closely in yielding much larger glacial-interglacial temperature changes than can be assumed purely on the basis of the delta records and the present relationship between delta values and temperature. The temperature increase from the coldest part of the last glaciation to the Holocene is about 21�C, about double the value that can be assumed based on a constant relationship between d18O values and temperature.
The question of whether only the long term variations follow a changed relation or whether the fast climatic variations are also larger than hitherto assumed remains open.
The fast climatic variations observed in the d18O record of Greenland ice cores would attract only limited attention if they were only local in character. However, there is ample evidence that these fast climatic fluctuations are also affecting regions far away from Greenland. Indeed, there is good correlation between some of the fast climatic variations observed in the Greenland ice cores and variations observed in deep sea sediment cores from the North Atlantic.
Therefore, it is assumed that the deep water formation in the North Atlantic plays a key role in the fast climatic variations. However, the climatic signal is not only seen in the North Atlantic region. The fact that methane levels correlate well with the variations, with high methane concentrations in mild periods, shows that low latitude regions (the main source for methane at this time) were also influenced by these fast variations.
After the d18O analyses performed on O2 extracted from air bubbles, which allow time scales of Greenland ice cores and Antarctic ice cores to be synchronised, it became evident that the major events are also recorded in the isotopic temperature record from the Vostok core. However, the events in Antarctica were apparently of smaller amplitude and more ramped appearance than in Greenland.
Methane with its main source in low latitude wetlands during the last glacial period and the early Holocene is an indicator of bioactivity, in this special case of the bioactivity of wetlands in low latitudes. More parameters which are bioindicators have been measured on the GRIP ice core, such as ammonium and organic acids.
The comparison of records of these parameters is still quite puzzling at present. The records deviate considerably from each other, indicating that each parameter is sensitive to other characteristics of bioactivity or influenced by a different region. While methane shows a distinct concentration minimum during the "Younger Dryas" period, NH4+ shows rather a maximum.
The source for methane is assumed to be all wetlands in low latitudes, while the source for NH4+ the soil bioactivity of parts of North America. The interpretation of these parameters is still at an early stage, but the investigations on the GRIP ice core show clearly that ice cores have the potential also to give information about the biosphere in the past.
The GRIP ice core data suggested that rapid climatic oscillations like the ones during the ice age persisted during the previous warm period (the Eemian period). The GISP-2 core also shows rapid oscillations during that period, but with different timing and character.
Therefore, the question arose whether one or both cores are affected by stratigraphic disturbances. Careful physical examinations of both cores showed that significant structural disturbances occurred in both cores above the depth where differences between the two cores started (about 2,800 m below snow surface corresponding to an age of about 110,000 years).
The results from methane and d18O measurements on O2 from bubbles and their comparison with results from Antarctic ice cores show that the ice at least partly represents the Eemian period. However they also give evidence of stratigraphic disturbances affecting at least some of the fast variations.
However, the role of stratigraphic disturbances cannot be settled until ice flow modellers can explain the kind and the mechanisms of such disturbances.
This will be a difficult task, especially for the very short cold periods where the ice layer with completely different characteristics is only about 0.2 m thick. Hope remains that much can be learned about the Eemian climate from the existing two cores. Ultimately, just as these cores were needed to validate the rapid oscillations already observed in the Camp Century and Dye3 cores, a new core, where the Eemian period is farther above bedrock, will be needed to give a final answer.
Greenland Ice Core Project
An ESF Research Programme
Final Report
