The Thermal Effects of Magma On Ocean Heating Through Ice Ages Cycles, With Particular Reference to Interglacial Events
24 Pages Posted: 25 Oct 2018 Last revised: 10 Jul 2019
Date Written: October 2, 2018
The direct heating of oceans by volcanism is estimated using current knowledge, and extended to consider its variation through ice age cycles. The crude estimate of the current effect is c.0.7W/m2, from c.100,000 volcanoes releasing magma volumes whose intrusion would raise sea levels c. 8mm pa, without compensating effects. A doubling of this level can deliver the minimum incremental heat required to produce an interglacial event over 7Ka, assuming no losses. Such an effect is strongly supported by the available emissions evidence.
The primary cause of the variability of emissions from the thin oceanic crust is suggested to be peak solid gravitational tides, caused by the maximum variation of Milankovitch orbital eccentricities on Earth's visco-elastic mantle. Only the 100Ka effect is now large enough to sustain an tnterglacial warming, possibly assisted by the unloading effects of >100m ocean level reduction at this time and other small positive feedbacks, such as glacial dust. These interglacial warmings are ultimately capped by the powerful feedback from warming oceans, through evaporative cooling and increasing cloud albedo that both cool the oceans and reduce solar insolation to impose the new and higher interglacial thermal equilibrium. This is maintained for a few Ka, until reducing gravitational stress, hence volcanic activity, return emissions to glacial period lows.
The significant sub aerial volcanic peaks occurring at obliquity and precessional Milankovitch maximums must vary the emissions within individual 100Ka cycles, as these motions also arise from solid gravitational tides, caused by cyclical planetary alignments. Lesser causes of crustal deformation such as annual solid tides can create shorter, weaker and cyclical volcanic variability, and hence climate variability, adequate to energise the range of atmospheric equilibrium temperatures that characterise the ice age. To refine the above conclusions with greater precision will require improved submarine volcano emissions data, and physical correlation of this activity with changing global temperatures.
Keywords: Magma, Interglacial, Climate, Gravitational Tides, Milankovitch
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