A non-linear climate oscillator controlled by biogeochemical cycling in the ocean: an alternative model of Quaternary ice age cycles |
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| Authors: | Gary Shaffer |
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| Institution: | (1) Oceanographic Institute, University of Gothenburg, Box 4038, S-40040 Gothenburg, Sweden |
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| Abstract: | A new, biogeochemical model of ice age cycles is developed and applied which explains major features of climate variations in the late Quaternary —rapid ice age terminations, large glacial-interglacial amplitudes and  100-kyr cycles — in a way consistent with the paleorecord. Existing models which invoke non-linear, ice-sheet-earth-crust dynamics to explain ice age cycles are not consistent with simultaneous terminations in both hemispheres and other phase relationships implied by the paleorecord. The present model relates climate change to oscillations of oceanic primary (new) production controlled by the availability of inorganic nitrogen. Large oscillations follow shelf erosion events triggered by small sea-level drops. These drops are due to glacial buildup associated with a minimum in Northern Hemisphere insolation. Rapid global warming at terminations is initiated by open ocean denitrification events leading to new production crashes and rapid modification of atmospheric trace gas concentrations (CO2, DMS, N2O). Other feedbacks of the land-ice-atmosphere-ocean system control the rest of the climate cycle. 100-kyr cycles derive from orbital pacemaking of the strong, low-frequency model response. Results suggest that the climate regime transition near 800 kyr B.P. may be related to changes in the continental shelf slope, that existing chronologies based on orbital tuning may need to be revised and that temporary increases in atmospheric N2O concentrations at terminations, due to the denitrification events, may have caused significant  greenhouse warming. A spike of elevated N2O concentration at terminations may be recorded in polar ice. |
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