The Effect of Orbital Cycles on Late and Middle Cretaceous Climate: A Comparative General Circulation Model Study

  1. P. L. de Boer4 and
  2. D. G. Smith5
  1. J. Park1 and
  2. R. J. Oglesby2,†

Published Online: 29 APR 2009

DOI: 10.1002/9781444304039.ch30

Orbital Forcing and Cyclic Sequences

Orbital Forcing and Cyclic Sequences

How to Cite

Park, J. and Oglesby, R. J. (1994) The Effect of Orbital Cycles on Late and Middle Cretaceous Climate: A Comparative General Circulation Model Study, in Orbital Forcing and Cyclic Sequences (eds P. L. de Boer and D. G. Smith), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304039.ch30

Editor Information

  1. 4

    Utrecht, The Netherlands

  2. 5

    London, UK

Author Information

  1. 1

    Department of Geology and Geophysics, Yale University, P.O. Box 6666, New Haven, CT 06511, USA

  2. 2

    Department of Geological Sciences, Brown University, P.O. Box 1846, Providence, RI 02912-1846, USA

  1. Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, IN 47907, USA

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 28 JAN 1994

ISBN Information

Print ISBN: 9780632037360

Online ISBN: 9781444304039

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Keywords:

  • effect of orbital cycles on Late and Middle Cretaceous climate;
  • atmospheric general circulation model (GCM);
  • model sensitivity coefficients;
  • palaeotemperature data;
  • sea surface temperaturew

Summary

We use sets of climate simulations made with the NCAR (National Center for Atmospheric Research) atmospheric general circulation model (GCM) CCM1 to perform a comparative sensitivity study using two different reconstructions of Cretaceous orography and sea-surface temperatures (SSTs). One set of boundary conditions is appropriate for 100 Ma (Mid-Cretaceous) and has SSTs determined largely by the local surface energy balance as computed in a previous GCM simulation of the Mid-Cretaceous climate. The other set of boundary conditions is appropriate for 70 Ma (Late Cretaceous) and has SSTs determined largely by palaeotemperature data drawn from that time period, which suggest a weak meridional (north–south) SST gradient. No land or sea ice is allowed in either set of climate simulations. We estimated the linear sensitivity of key model variables to precession and obliquity as functions of latitude and longitude. The mean climates for the two reconstructions differ greatly. The hydrological cycle in the 100-Ma simulations shares two critical features with that of the present-day Earth: (i) a symmetric pattern of zonally averaged net evaporation minus precipitation (EP) about the equator, indicative of a low-latitude Hadley-cell circulation and the intertropical convergence zone (ITCZ); and (ii) a west–east/arid–wet asymmetry induced by the summer monsoon over large low-latitude land masses. Both of these features are absent or greatly modified in the 70-Ma simulations, and we infer that they are inhibited by the weak meridional SST gradient from the equator to roughly 40° latitude in the summer hemisphere. The atmospheric circulation in the 70-Ma reconstruction is very sluggish relative to the 100-Ma circulation. Orbital insolation variations in the 100-Ma simulations amplify or diminish monsoonal pressure anomalies and the mean wind flow around them. Associated with these are large changes in the atmospheric hydrological cycle. Large shifts in the evaporation–precipitation balance (EP) over the newly rifted equatorial South Atlantic and East Tethys can be related speculatively to large-scale changes in ocean circulation and the development of deep-water anoxia. Insolation-induced changes in the monsoonal pressure anomalies in the 70-Ma simulations affect the hydrological cycle less strongly at low latitudes. We infer that the weak meridional SST gradient in the low-latitude summer hemisphere inhibits a large response by the hydrological cycle in this region. However, warmer mid-latitude SSTs in the 70-Ma simulations raise the specific humidity of mid-latitude atmospheric flows, thereby increasing the potential for a large hydrological response to precession and obliquity over North America and proto-Europe, where many examples of cyclic limestone sequences can be found. The presence of epicontinental seas, however, inhibits the formation of a summertime monsoon in North America for our 70-Ma simulations, resulting in a weak response in this region to Milankovitch insolation fluctuations. Our conclusion that the SST profile controls the model behaviour is supported by zonal averages of the model's response to orbital insolation fluctuations, which are small relative to zonal averages of the models ‘mean-state’ Cretaceous climate.