| 1. |
- Roethlisberger, R., et al.
(författare)
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The Southern Hemisphere at glacial terminations : insights from the Dome C ice core
- 2008
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Ingår i: Climate of the past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 4:4, s. 345-356
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Tidskriftsartikel (refereegranskat)abstract
- The many different proxy records from the European Project for Ice Coring in Antarctica (EPICA) Dome C ice core allow for the first time a comparison of nine glacial terminations in great detail. Despite the fact that all terminations cover the transition from a glacial maximum into an interglacial, there are large differences between single terminations. For some terminations, Antarctic temperature increased only moderately, while for others, the amplitude of change at the termination was much larger. For the different terminations, the rate of change in temperature is more similar than the magnitude or duration of change. These temperature changes were accompanied by vast changes in dust and sea salt deposition all over Antarctica. Here we investigate the phasing between a South American dust proxy (non-sea-salt calcium flux, nssCa(2+)), a sea ice proxy (sea salt sodium flux, ssNa(+)) and a proxy for Antarctic temperature (deuterium, delta D). In particular, we look into whether a similar sequence of events applies to all terminations, despite their different characteristics. All proxies are derived from the EPICA Dome C ice core, resulting in a relative dating uncertainty between the proxies of less than 20 years. At the start of the terminations, the temperature (delta D) increase and dust (nssCa(2+) flux) decrease start synchronously. The sea ice proxy (ssNa(+) flux), however, only changes once the temperature has reached a particular threshold, approximately 5 degrees C below present day temperatures (corresponding to a delta D value of -420 parts per thousand). This reflects to a large extent the limited sensitivity of the sea ice proxy during very cold periods with large sea ice extent. At terminations where this threshold is not reached (TVI, TVIII), ssNa(+) flux shows no changes. Above this threshold, the sea ice proxy is closely coupled to the Antarctic temperature, and interglacial levels are reached at the same time for both ssNa(+) and delta D. On the other hand, once another threshold at approximately 2 degrees C below present day temperature is passed (corresponding to a delta D value of -402 parts per thousand), nssCa(2+) flux has reached interglacial levels and does not change any more, despite further warming. This threshold behaviour most likely results from a combination of changes to the threshold friction velocity for dust entrainment and to the distribution of surface wind speeds in the dust source region.
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| 2. |
- Svensson, A., et al.
(författare)
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A 60 000 year Greenland stratigraphic ice core chronology
- 2008
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9332. ; 4:1, s. 47-57
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Tidskriftsartikel (refereegranskat)abstract
- The Greenland Ice Core Chronology 2005 (GICC05) is a time scale based on annual layer counting of high-resolution records from Greenland ice cores. Whereas the Holocene part of the time scale is based on various records from the DYE-3, the GRIP, and the NorthGRIP ice cores, the glacial part is solely based on NorthGRIP records. Here we present an 18 ka extension of the time scale such that GICC05 continuously covers the past 60 ka. The new section of the time scale places the onset of Greenland Interstadial 12 (GI-12) at 46.9 +/- 1.0 ka b2k (before year AD 2000), the North Atlantic Ash Zone II layer in GI-15 at 55.4 +/- 1.2 ka b2k, and the onset of GI-17 at 59.4 +/- 1.3 ka b2k. The error estimates are derived from the accumulated number of uncertain annual layers. In the 40-60 ka interval, the new time scale has a discrepancy with the Meese-Sowers GISP2 time scale of up to 2.4 ka. Assuming that the Greenland climatic events are synchronous with those seen in the Chinese Hulu Cave speleothem record, GICC05 compares well to the time scale of that record with absolute age differences of less than 800 years throughout the 60 ka period. The new time scale is generally in close agreement with other independently dated records and reference horizons, such as the Laschamp geomagnetic excursion, the French Villars Cave and the Austrian Kleegruben Cave speleothem records, suggesting high accuracy of both event durations and absolute age estimates.
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