Arctic sea ice helps remove CO2 from the atmosphere - Innovations Report

[Michael Hayes]

"The chemical removal of CO2 in sea ice occurs in two phases. First crystals of calcium carbonate are formed in sea ice in winter. During this formation CO2 splits off and is dissolved in a heavy cold brine, which gets squeezed out of the ice and sinks into the deeper parts of the ocean. Calcium carbonate cannot move as freely as CO2 and therefore it stays in the sea ice. In summer, when the sea ice melts, calcium carbonate dissolves, and CO2 is needed for this process. Thus, CO2 gets drawn from the atmosphere into the ocean – and therefore CO2 gets removed from the atmosphere”, explains Dorte Haubjerg Søgaard.

The biological removal of CO2 is done by algae binding of carbon in organic materials."

https://www.innovations-report.com/earth-sciences/arctic-sea-ice-helps-remove-co2-from-the-atmosphere/ 

MH] The sea ice cycle seems to be a form of mCDR. How one would translate that into deployable technology would be the obvious question. The scale needed dictates that any proposed method would need to have a low to no cost operations ability as there are no marketable byproducts in producing ice besides the ice itself. Finding non C credit dependent financial support is likely needed. 

Teaching others, especially grant providers, that sea ice is a natural CO2 management tools is also needed. 

[Klaus Lackner]

Since seawater is supersaturated in CaCO3, the dissolution would have to happen on top of the ice, and draw its CO2 from the ambient air above it. That I would think is kinetically limited.  To the extent that the ice melts at the bottom of the ice that is exposed to warming seawater in the spring, the carbonate will likely sink to the ocean floor, in effect taking alkalinity away from the ocean water column. (So now we are relying on the CO2 that sank not to return to the surface where it would outgas.)  Whether bottom melting or top melting will dominate is difficult to say, but for freshwater melt to dissolve the carbonate requires sufficient exposure time to ambient air to suck up CO2 and dissolve the crystal structure, before the water flows into the sea an gets mixed with seawater to the point that it is supersaturated in calcium carbonate.  Your best bet is probably rain hitting the surface of the ice, but even though the pH of rainwater is low, there is very little CO2 available.  In any event, to the extent that the freeze/thaw cycle results in carbonate additions to the sediment, the net effect is a reduction in the ocean’s ability to hold CO2.

 

 

 

 

 

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[Michael Hayes]

Overall, sea ice melt is increasing Arctic water acidification, and sea ice production clearly has the opposite results due to the physical barrier between the water and air. If so, why would sea ice production not be considered an OAE method? 

Moreover, why is the brine production, which drags surface GHGs to the seabed, not recognized as a CDR? Sending biomass to the seabed is recognized as such.