De. Pollock, THE ROLE OF DIATOMS, DISSOLVED SILICATE AND ANTARCTIC GLACIATION IN GLACIAL INTERGLACIAL CLIMATIC-CHANGE - A HYPOTHESIS/, Global and planetary change, 14(3-4), 1997, pp. 113-125
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.