Cenomanian climate zones
New thoughts about the cretaceous climate and oceans
1. William W. Hay (a)
2. Sascha Floegel (b)
a Department of Geological Sciences, University of Colorado at Boulder, 2045 Windcliff Dr. Estes Park, CO 80517, USA
b. GEOMAR | Helmholtz-Zentrum für Ozeanforschung Kiel, Gebäude Ostufer, Wischhofstr. 1–3, D-24148 Kiel, Germany
Several new discoveries suggest that the climate of the Cretaceous may have been more different from that of today than has been previously supposed. Detailed maps of climate sensitive fossils and sediments compiled by Nicolai Chumakov and his colleagues in Russia indicate widespread aridity in the equatorial region during the Early Cretaceous. The very warm ocean temperatures postulated for the Mid-Cretaceous by some authors would likely have resulted in unacceptable heat stress for land plants at those latitudes, however, and may be flawed.
Seasonal reversals of the atmospheric pressure systems in the Polar Regions are an oversimplification. However, seasonal pressure difference between 30° and 60° latitude become quite pronounced, being more than 25 hPa in winter and less than 10 hPa in summer. This results in inconstant winds, affecting the development of the gyre-limiting frontal systems that control modern ocean circulation. The idea of Hasegawa et al. (2011) who suggest a drastic reduction in the size of the Hadley cells during the warm Cretaceous greenhouse is supported by several numerical climate simulations. Rapid contraction of the Hadley cell such that its sinking dry air occurs at 15° N latitude rather than 30° N is proposed to occur at a threshold of 1,000 ppmv CO2 in the atmosphere. This change will probably be reached in the next century.
There is a really, really important chunk here about RUBISCO: the equatorial terrestrial environment may have been a wasteland and lifeless at times. Huber pointed this out about the PETM as well. It is entirely possible we could get to that point with global warming/climate change. The above, btw, does not address as far as I can see, the evidence of ice in Australia during the early cretaceous.