A Climactic Feedback? Variations in Mid-Ocean Ridge CO2 Emissions Driven by Glacial Cycles

Abstract:

Changes in sea level associated with glacial cycles affect the pressure beneath a mid-ocean ridge (MOR) ^_[1,2,3]. Pressure controls the depth of first melting, and therefore the rate of change of pressure controls the rate of change of the depth of first melting. The changing depth of first melting alters the effective rate at which mantle, and thus CO₂, enters the melting region. Melt then transports CO₂ to the ridge axis, where it enters the climate system. We calculate that the lag between sea level change and consequent variation in MOR CO₂ emissions is 40-120 kyrs^_[4], similar to the timescale of glacial cycles. Could these variations in MOR CO₂ emissions feed back on climate and lead to ice-age pacing at a small multiple of the obliquity period? ^[5]

To test this hypothesis we begin with a climate model comprised of a global energy balance and a 1D ice sheet. The ice sheet flows under its own weight, accumulates due to precipitation, and melts in response to the local energy balance^[6]. This model broadly replicates Early Pleistocene 40 kyr glacial cycles. We extend the model to include a variable greenhouse effect, according to atmospheric CO₂, and variable MOR CO₂ emissions driven by sea level. The lag between sea level change and MOR CO₂ emissions is controlled by mantle permeability. If this model does not demonstrate MOR CO₂ emissions altering glacial cycles, it would suggest this hypothesised feedback mechanism can be rejected.

 

References

[1] Huybers & Langmuir 2009; 10.1016/j.epsl.2009.07.014
[2] Lund & Asimow 2011; 10.1029/2011GC003693
[3] Crowley et al 2015; 10.1126/science.1261508
[4] Burley & Katz 2015; 10.1016/j.epsl.2015.06.031
[5] Huybers (in prep.)
[6] Huybers & Tziperman 2008; 10.1029/2007PA001463