THE ROLE OF DIATOMS, DISSOLVED SILICATE AND ANTARCTIC GLACIATION IN GLACIAL INTERGLACIAL CLIMATIC-CHANGE - A HYPOTHESIS/

A new theory is proposed to explain global cooling at the onset of Ple istocene glacial periods. Atmospheric CO2 drawdown is considered to be the driving force behind global cooling, brought about by heightened productivity at the equatorial divergences and along continental margi ns, particularly in upwelling regions. Eutrophication appears to be tr iggered when global warming during late interglacial periods causes ac celerated melting of the West Antarctic Ice Sheet. This would release large reserves of silicate-enriched subglacial meltwaters into the sur rounding oceans where entrainment would take place into deep and inter mediate currents forming in Antarctic and subantarctic waters. Subsequ ent advection, mixing and upwelling of silicate-enriched deep and inte rmediate waters into the coastal zones and open-ocean divergences resu lts in the proliferation of large, rapidly-sinking diatom species with a high affinity for dissolved silicate. These blooms enhance rates of recycling of N and P in upwelling regions and accelerate rates of org anic carbon production, export and sequestration in shelf and slope se diments and in the deep sea. The resultant atm. CO2 drawdown initiates global cooling. Consequent expansion of Northern Hemisphere glaciers lowers sea level, while increased temperature and pressure gradients b etween equatorial and polar regions intensify meridional winds. The fo rmer process exposes nutrient-enriched coastal sediments to wave erosi on, thereby releasing new nutrient supplies, while the latter process enhances upwelling. The combined effect is to greatly increase rates o f org. C production and export from continental margins and further ac celerate arm. CO2 drawdown. Glacial-period cooling is also enhanced by a number of other positive feedbacks, including changes in albedo, wa ter vapour and cloud cover. Episodic warming intervals during glacial periods may be related to insolation changes associated with orbital p recession and tilt cycles, but processes involved in deglaciation and reversion to the interglacial climatic regime are complex and not yet fully understood.