Dansgaard-Oeschger event

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Climate proxy : Dansgaard-Oeschger events can be seen in four ice cores from the last 140,000 years in the northern, but not the southern hemisphere.

Dansgaard-Oeschger events (short: DO events) are rapid climatic fluctuations during the last glacial period . 23 such events were found between 110,000 and 23,000  BP . Dansgaard-Oeschger events are named after Willi Dansgaard and Hans Oeschger .

In the northern hemisphere , they present themselves as periods of rapid warming followed by slow cooling. The process takes place over a longer period of time, which is typically described on scales of centuries .

causes

The underlying process for the occurrence and the amplitude of the event are still unclear. The effect of the event in the southern hemisphere with slower warming and much smaller temperature fluctuations is significantly different from that of the northern hemisphere. The existence of the Dansgaard-Oeschger events was therefore only widely recognized after the Greenland ice drilling projects GRIP and Greenland Ice Sheet Project (GISP) had been evaluated , although evidence of the phenomenon was already found in the ice core that was taken from the Vostok station .

Detail around 40,000 BC BC, comparative measurements between two nuclei

Dansgaard-Oeschger events are related to Heinrich events . Heinrich events are interruptions in thermohaline circulation that cause cooling in the northern hemisphere. A cooler climate leads to an enlargement of the ice surface and thus a higher albedo of the earth's surface, which intensifies the cooling. There are indications that Dansgaard-Oeschger events occur globally synchronized.

In 2003, the climate researcher Stefan Rahmstorf identified a 1470-year cycle in which the phenomenon occurred. Ocean circulation modes were suggested as an explanation for the events in 2004. In a follow-up study, which was carried out in 2005, the periodicity could be traced back to a superposition of two known activity cycles of the sun . After 1470 years, the 210 cycle of solar activity ( Suess-de Vries cycle ) has expired seven times and the 86.5 cycle ( Gleißberg cycle ) seventeen times .

The deviations from this cycle amounted to about ± 12% in the last 50,000 years according to the measurements of the GISP2 (± 2% in the five most recent events, the data of which can be recorded particularly precisely). In contrast, neither older parts of the GISP2 core nor comparable events in the GRIP core show such regularity, which could be explained with varying degrees of reliability, in particular more precise shift counting for the first 50,000 years of the GISP2 core.

history

In retrospect, the Dansgaard-Oeschger anomalies can also be found in other cores ( GISP , Century Greenland ). Dansgaard et al. noted the existence in the GRIP core as "violent oscillations" in the δ 18 O signal , which seemed to correlate with earlier Camp Century cores 1400 km away. Dansgaard et al. speculated that these could be related to quasi-stationary modes of the atmosphere - ocean system .

literature

  • Willi Dansgaard , James WC White, Sigfus J. Johnson (1989): The abrupt termination of the Younger Dryas climate event , Nature. 339: 532-533 doi : 10.1038 / 339532a0
  • Willi Dansgaard, Sigfus J. Johnsen, Henrik B. Clausen, Dorthe Dahl-Jensen, Niels S. Gundestrup, Claus U. Hammer, CS Hvidberg, JP Steffensen, Árny E. Sveinbjornsdottir, Jean Jouzel, Gerard C. Bond: Evidence for general instability of past climate from a 250-kyr ice-core record. Nature, 364, pp. 218-220, 1993 doi : 10.1038 / 364218a0
  • Xu Zhang, Gerrit Lohmann, Gregor Knorr, Conor Purcell (2014): Abrupt glacial climate shifts controlled by ice sheet changes , Nature, 2014 doi : 10.1038 / nature13592

Individual evidence

  1. ↑ Bond et al .: The North Atlantic's 1–2 kyr climate rhythm: relation to Heinrich events, Dansgaard / Oeschger cycles and the little ice age Archived from the original on October 29, 2008. In: PU Clark, RS Webb, LD Keigwin ( Ed.): Mechanisms of Global Change at Millennial Time Scales. Geophysical Monograph 112 . 1999, pp. 59-76.
  2. ↑ Stefan Rahmstorf: Timing of abrupt climate change: A precise clock . In: Geophys. Res. Lett. . 30, No. 10, 2003, p. 1510. doi : 10.1029 / 2003GL017115 .
  3. ↑ Stefan Rahmstorf, 2004. Abrupt climate change (PDF; 121 kB)
  4. ↑ Holger Braun, Marcus Christl, Stefan Rahmstorf et al. (2005): Possible solar origin of the 1,470-year glacial climate cycle demonstrated in a coupled model , in: Nature, Vol. 438, pp. 208–211 doi : 10.1038 / nature04121 (PDF; 472 kB)
  5. ↑ http://www.ncdc.noaa.gov/paleo/icecore/greenland/gisp/campcentury/campc.html (accessed May 5, 2010)