Atmospheric and Ocean Thermodynamics in Quaternary Climate Change

The “saw-tooth pattern” fluctuation shown in proxy data time series of Vostok ice core analysis has been a great puzzle in the study of Earth's natural climate change. Hypotheses for the mechanism creating the fluctuation propose several climate drivers. These include Earth's orbital variation (Milankovitch cycles), albedo effect, greenhouse gases (GHGs), methane hydrate (MH), volcanoes, aerosols, dust, geothermal effect, etc. None of them can successfully explain the saw-tooth pattern. Here, we present a counter-intuitive mechanism to explain the causes of Quaternary climate change and the saw-tooth pattern.

First, the global integral of (albedo-modulated) insolation is almost in balance with Earth's long wave radiation. However, the residual energy flux [~ O(5 Wm-2)] has been stored (mostly) in ocean in the forms of heat and chemical energy (through photosynthesis). This is like charging a (heat) capacitor. The more insolation leads to higher temperature of seawater in the top layer of ocean, and therefore, the lower the seawater density. Second, the higher the seawater temperature is, the stronger the evaporation of seawater gets. That moves water from oceans to the atmosphere (to form clouds) and finally precipitates (into rain or snow). The latent heat loss from ocean keeps seawater temperature under a limit. Meanwhile, the rising seawater temperature reduces the solubility of gases dissolved in seawater. This causes the rise of atmospheric GHG concentrations. Third, the greenhouse effect of the GHGs traps more heat, creating a positive feedback to seawater temperature. Fourth, here comes a brake. The clouds and the ice sheet increase the albedo. That sets a cap on the total insolation received at surface. This brings the unavoidable glacial time. Fifth, the geothermal heat flux (~ 0.05 Wm-2 on average) from mid-ocean range is heating the seawater at the bottom of ocean. This is like charging another (heat) capacitor. We will explain how these two capacitors exchange energy through thermodynamic and chemical processes, how they become unstable and discharge, leading to a huge increase of temperature of both the atmosphere and oceans – the interglacial while the insolation is at a minimum! How MH and ice sheet jointly create those sharp saw-teeth is also discussed.

Acknowledgement: The support from National Science Council, Taiwan (grant number NSC952119M002048) is acknowledged.