Structure and origin of Holocene cold events

Heinz Wanner a,b,*, Olga Solomina c, Martin Grosjean a,b, Stefan P. Ritz b,d, Markéta Jetel a

Institute of Geography, University of Bern, Bern, Switzerland
b Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
c Institute of Geography, Russian Academy of Sciences, Moscow, Russia
d Climate and Environmental Physics, University of Bern, Bern, Switzerland
Quaternary Science Reviews Volume 30, Issues 21-22, October 2011, Pages 3109-3123 doi:10.1016/j.quascirev.2011.07.010

The present interglacial, the Holocene, spans the period of the last 11,700 years. It has sustained the growth and development of modern society. The millennial-scale decreasing solar insolation in the Northern Hemisphere summer lead to Northern Hemisphere cooling, a southern shift of the Intertropical  Convergence Zone (ITCZ) and a weakening of the Northern Hemisphere summer monsoon systems. On the multidecadal to multicentury-scale, periods of more stable and warmer climate were interrupted by several cold relapses, at least in the Northern Hemisphere extra-tropical area. Based on carefully selected 10,000-year-long time series of temperature and humidity/precipitation, as well as reconstructions of glacier advances, the spatiotemporal pattern of six cold relapses during the last 10,000 years was analysed  and presented in form of a Holocene Climate Atlas (HOCLAT; see research/projects/holocene_atlas/). A clear cyclicity was not found, and the spatiotemporal variability of temperature and humidity/precipitation during the six specific cold events (8200, 6300, 4700, 2700, 1550 and 550 years BP) was very high. Different dynamical processes such as meltwater flux into the North Atlantic, low solar activity, explosive volcanic eruptions, and fluctuations of the thermohaline  circulation likely played a major role. In addition, internal dynamics in the North Atlantic and Pacific area (including their complex interaction) were likely involved.



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