Orbital forcing of Arctic climate: mechanisms of climate response and implications for continental glaciation |
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| Authors: | C S Jackson A J Broccoli |
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| Institution: | (1) Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ 08542, USA;(2) NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, NJ 08542, USA;(3) Present address: Institute for Geophysics, The John A. and Katherine G. Jackson School of Geosciences, The University of Texas at Austin, 4412 Spicewood Springs Rd., Bldg 600, Austin, TX 78759, USA;(4) Present address: Department of Environmental Sciences, Rutgers University, New Brunswick, NJ 08903, USA |
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| Abstract: | Progress in understanding how terrestrial ice volume is linked to Earth s orbital configuration has been impeded by the cost of simulating climate system processes relevant to glaciation over orbital time scales (103–105 years). A compromise is usually made to represent the climate system by models that are averaged over one or more spatial dimensions or by three-dimensional models that are limited to simulating particular  snapshots in time. We take advantage of the short equilibration time ( 10 years) of a climate model consisting of a three-dimensional atmosphere coupled to a simple slab ocean to derive the equilibrium climate response to accelerated variations in Earths orbital configuration over the past 165,000 years. Prominent decreases in ice melt and increases in snowfall are simulated during three time intervals near 26, 73, and 117 thousand years ago (ka) when aphelion was in late spring and obliquity was low. There were also significant decreases in ice melt and increases in snowfall near 97 and 142 ka when eccentricity was relatively large, aphelion was in late spring, and obliquity was high or near its long term mean. These glaciation-friendly time intervals correspond to prominent and secondary phases of terrestrial ice growth seen within the marine  18O record. Both dynamical and thermal effects contribute to the increases in snowfall during these periods, through increases in storm activity and the fraction of precipitation falling as snow. The majority of the mid- to high latitude response to orbital forcing is organized by the properties of sea ice, through its influence on radiative feedbacks that nearly double the size of the orbital forcing as well as its influence on the seasonal evolution of the latitudinal temperature gradient. |
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