Conceptual model for millennial climate variability: a possible combined solar-thermohaline circulation origin for the ~1,500-year cycle
- 982 Downloads
Dansgaard-Oeschger and Heinrich events are the most pronounced climatic changes over the last 120,000 years. Although many of their properties were derived from climate reconstructions, the associated physical mechanisms are not yet fully understood. These events are paced by a ~1,500-year periodicity whose origin remains unclear. In a conceptual model approach, we show that this millennial variability can originate from rectification of an external (solar) forcing, and suggest that the thermohaline circulation, through a threshold response, could be the rectifier. We argue that internal threshold response of the thermohaline circulation (THC) to solar forcing is more likely to produce the observed DO cycles than amplification of weak direct ~1,500-year forcing of unknown origin, by THC. One consequence of our concept is that the millennial variability is viewed as a derived mode without physical processes on its characteristic time scale. Rather, the mode results from the linear representation in the Fourier space of nonlinearly transformed fundamental modes.
KeywordsRectification Solar forcing Thermohaline circulation Millennial variability Fundamental Derived climate modes
This study was supported by Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany (MARCOPOLI), by Alexander von Humboldt Foundation and University of Bucharest, Faculty of Physics, Romania through contract CEEX-112/2005. Thanks go to two anonymous referees for constructive and helpful comments and Drs. Norel Rimbu and Thomas Laepple for fruitful discussions.
- Clement AC, Cane MA (1999) Mechanisms of global climate change at millennial time scales. American Geophysics Union, WashingtonGoogle Scholar
- Dansgaard W, Johnsen SJ, Clausen HB, Dahl-Jensen D, Gundestrup N, Hammer CU, Oeschger H (1984) North Atlantic climate oscillations revealed by deep Greenland ice cores. Climate processes and climate sensitivity. Geophysical Monograph. Am. Geophys. Union 29:288–298Google Scholar
- Debret M, Bout-Roumazeilles V, Grousset F, Desmet M, McManus JF, Massei N, Sebag D, Petit JR, Copard Y, Trentesaux A (2007) The origin of the 1500-year climate cycles in Holocene North-Atlantic records. Clim Past 3:569–575Google Scholar
- Dima M, Lohmann G (2004) Fundamental and derived modes of climate variability. Concept and application to interannual variability. Tellus 56A:229–249Google Scholar
- Huybers P, Wunsch C (2003) Rectification and precession signals in the climate system. Geophys Res Lett 30(3–1):3–4Google Scholar
- Rimbu N, Lohmann G, Lorenz SJ, Kim JH, Schneider R (2004) Holocene climate variability as derived from alkenone sea surface temperature reconstructions and coupled ocean-atmosphere model experiments. Clim Dynam 23:215–227Google Scholar
- Schulz M, Paul A (2002) Holocene climate variability on centennial-to-millennial time scales: 1; Climate records from the North-Atlantic Realm; Climate development and history of the North Atlantic Realm. Springer, Heidelberg, pp 41–54Google Scholar
- Witt A, Schumann AY (2005) Holocene climate variability on millennial scales recorded in Greenland ice cores. Nonlinear Processes Geophys 12:345–352Google Scholar