| Abstract: | Circulation of the ocean reflects a long-term integration of the atmospheric circulation. Today the surface of the ocean is characterized by tropical-subtropical anticyclonic gyres and polar cyclonic gyres separated by frontal systems that are the origin of the ocean pycnocline. This surficial oceanic circulation system is driven by the winds. It is a clear reflection of the 3-cell per hemisphere atmospheric circulation system that exists but is characterized by high latitude variability in the form of Rossby waves separating the polar and intermediate cells. The surface circulation carries about 80% of the global ocean heat transport; the remainder is characterized by the thermohaline circulation system that today involves sinking of water at small high-latitude sources and broad slow upwelling throughout the tropics and equatorial regions.
The geologic record of the Cretaceous and early Cenozoic ocean does not reflect this pattern of circulation. There is little evidence for oceanic frontal systems although fronts do exist in shallower, narrow meridional seaways.
Recent climate simulations for the Turonian suggest that atmospheric circulation in the Cretaceous may alternate seasonally between 3-cell and 2-cell systems. Today the stability of the 3-cell circulation is forced by ice in the high latitudes, which ensures polar high pressure systems throughout the year. The lack of polar ice in the Cretaceous and early Cenozoic results in an alternation between polar highs in the summer and lows in the winter. With such unstable atmospheric circulation, only the equatorial portions of the oceanic tropical-subtropical anticyclonic gyres would be well developed, with unstable boundaries characteristic of the polar regions. This would result in a less well developed oceanic pycnocline. Further, the lesser wind speeds of the Cretaceous, coupled with the more intense hydrologic cycle of a warmer Earth, might bring the wind-induced and evaporation/precipitation-induced ocean surface topography more nearly into balance, further destabilizing ocean circulation. With lesser pycnocline stability, and with warmer global temperatures, the ocean thermohaline circulation system might take on a larger role in global energy transport system. |