Until now, experts thought that, especially over the past 1. But as his study, which has now been published in the scientific journal Nature Communications , shows, there were also repeated irregularities during the period between 2. This dataset consists of a global evaluation of core samples from deep-sea sediments that are millions of years old, and includes measurements from the ancient shells of microscopic, single-celled marine organisms -- foraminifera -- that were deposited on the ocean floor.
Foraminifera incorporate oxygen from the seawater into their calcium shells. But over millennia, the level of specific oxygen isotopes -- oxygen atoms that have differing numbers of neutrons and therefore different masses -- varies in seawater. The LR04 dataset contains measurements of the ratio of the heavy oxygen isotope 18O to the lighter 16O. But there is also another effect that leads to relatively large amounts of 18O being found in the foraminifera's shells in glacial periods: when, during the course of a glacial period, there is heavy snowfall on land, which leads to the formation of thick ice sheets, the sea level falls -- in the period studied, by as much as m.
Since 18O is heavier than 16O, water molecules containing this heavy isotope evaporate less readily than molecules containing the lighter isotope. As such, comparatively more 18O remains in the ocean and the 18O content of the foraminifera shells increases. But using 18O values doesn't allow us to say whether prehistoric glaciation chiefly occurred in the Northern Hemisphere or in Antarctica.
The data was fed into a computer model that simulates the growth and melting of the large continental ice sheets. What sets it apart: the model is capable of separating the influence of temperature and that of sea level change on the 18O concentration. Furthermore, it can accurately analyse where and when snow falls and the ice increases -- more in the Northern Hemisphere or in Antarctica. With the oldest ice core recovered to date, 'EPICA', they have 'only' travelled back roughly , years into the past.
Climate Feedback. Ocean Acidification. Rising Sea Level. Marshak, Earth: Portrait of a Planet, 3rd ed.
New York: W. Norton, Part VI, pp. The frequency of extreme events represents an essential benchmark for climate change adaptation measures, since, when it comes to flood protection, transport and building materials, we need to be prepared for the worst-case scenario, and not just for "average" changes. To date it has been assumed that temperatures varied greatly during the last glacial, while the current interglacial was largely characterised by small temperature variations.
This interpretation was based on water isotope data from central Greenland ice cores. The team, led by Dr Kira Rehfeld and Dr Thomas Laepple, compared the Greenland data with that from sediments collected in several ocean regions around the globe, as well as from ice-core samples gathered in the Antarctic. They demonstrate that the phenomenon of major temperature fluctuations during glacial periods has by no means manifested uniformly worldwide, but has instead varied from region to region.
For instance, in the Tropics the temperature variations were three times as intense as today at the height of the last glacial, whereas the ice cores from Greenland indicate variations that were 70 times as intense. The achievement of first author Kira Rehfeld and her colleagues: they have for the first time gathered and compared data from diverse climate archives and a total of 99 research sites.
In the climate research community, ice cores are generally considered the gold standard, because their layers are highly consistent, unlike sediment layers from the seafloor, which are frequently marred by tectonic shifts, currents or marine organisms.
The AWI researchers have devised mathematical methods that allow them to estimate the uncertainties and potential sources of error while assessing various paleoclimate archives, and to take these factors into account in their analyses.
The more intensive variations during glacial periods are due to the greater difference in temperature between the ice-covered polar regions and the Tropics, which produced a more dynamic exchange of warm and cold air masses.
Climate modellers had previously postulated the mechanism of reduced variability under warmer climatic conditions in Yet with their analysis, Rehfeld, Laepple and colleagues are the first to reinforce this theory with global climate data from the past.
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