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Study: Volcanic trigger of ocean deoxygenation during Cordilleran ice sheet retreat

>Abstract

>North Pacific deoxygenation events during the last deglaciation were sustained over millennia by high export productivity, but the triggering mechanisms and their links to deglacial warming remain uncertain. Here we find that initial deoxygenation in the North Pacific immediately after the Cordilleran ice sheet (CIS) retreat was associated with increased volcanic ash in seafloor sediments. Timing of volcanic inputs relative to CIS retreat suggests that regional explosive volcanism was initiated by ice unloading. We posit that iron fertilization by volcanic ash during CIS retreat fuelled ocean productivity in this otherwise iron-limited region, and tipped the marine system towards sustained deoxygenation. We also identify older deoxygenation events linked to CIS retreat over the past approximately 50,000 years. Our findings suggest that the apparent coupling between the atmosphere, ocean, cryosphere and solid-Earth systems occurs on relatively short timescales and can act as an important driver for ocean biogeochemical change.

Some may be wondering... can this happen today with the rapid retreat of glaciers, ice caps and ice sheets?

Not really, not for the majority of the globe. As an example, the Cordilleran ice sheet, at its maximum extent contained a sea-level equivalent comparable to that of the present-day Greenland Ice Sheet^1, ^2 That amount of mass pushing down the crust simply isn't there anymore to yield the degree of decompression melting required to produce that much melt (magma) and ultimately trigger a volcanic response.

What about Greenland and Antarctica?

As far as Greenland goes, it doesn't seem likely we'll see any activity there as there are no active volcanoes in Greenland, nor are there any known mapped, dormant volcanoes under the Greenland ice sheet that were active during the Pliocene period of geological history that began more than 5.3 million years ago (volcanoes are considered active if they’ve erupted within the past 50,000 years).

Antarctica, however, does have active volcanoes. I suspect that with the rapid deglaciation of the Antarctic Ice Sheet it may be possible to see an increase in volcanic activity regionally. Though due to its location (at the south pole), and the circumpolar winds and currents, any volcanic ash would also be quite limited globally and would likely remain at the poles rather than spreading out and having any major climatic effects.

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I'm sure that could be part of it, but the ice melt during certain phases was so incredibly rapid that a theory was proposed that it was accelerated due to the top of the ice falling in altitude. As the altitude at the top of the ice sheet declines it encounters denser air which is warmer, this effectively created a rapid feedback that collapsed the Laurentide ice saddle across North America.