# What is the importance of mixing caused by outgassing in the ocean?

I have been asked the following question for which I have no clear answer: What is the relative importance on mixing of the vertical flow of gases (e.g., Oxygen produced by photosynthesis, CO2 produced in respiration, methane produce from hydrates) in the ocean water column? How does the mixing compare with physical mixing (e.g., wind, internal wave breaking) and molecular diffusion?

My first thought is that the ocean tends to not be saturated in oxygen and CO2, but is there some outgassing as a result of those processes? The question of methane hydrates is probably more complex and likely has links to climate change.

• I am curious, but I am having a hard time understanding the question - there seem to be a few questions embedded in here. Is it possible to construct a single, more concise question? – Isopycnal Oscillation Nov 2 '14 at 7:11
• @IsopycnalOscillation: I think it's pretty clear: The ocean is mixed by a number of processes (meridional overturning, thermohaline overturning, diffusion, eddies, giant squid...). One of those sources of mixing is up-welling gasses released by the ocean floor. How important is that source relative to all of the others combined (once you take absorption into account)? – naught101 Feb 9 '16 at 1:42
• @naught101 Totally agree. Not sure what I was thinking. Great question. – Isopycnal Oscillation Feb 9 '16 at 23:45

## 1 Answer

Outgassing is a process by which $O_{2}$, $CO_{2}$ and other chemicals are released as a result of heat or increase in temperature. It is different from advection and diffusion which are mixing processes as a result of temperature and concentration gradient. Outgassing is an abrupt release of gases from where they are stored trapped dissolved, in this case $O_{2}$ and $CO_{2}$ in the ocean. Like the ocean some materials are prone to outgassing when heated. For example chemicals released from plastics (e.g. the odor of a new car).

What is the relative importance on mixing of the vertical flow of gases in the ocean water column? How does the mixing compare with physical mixing (e.g., wind, internal wave breaking) and molecular diffusion?

The rate of outgassing in ocean is comparable to molecular diffusion of the gases. However, the mechanisms of outgassing and diffusion are different,i.e, outgassing occurs due to some sort of pumping mechanism but diffusion occurs due concentration gradient. Both mechanisms are important to stratify saturation,i.e. homogeneous distribution of chemicals. Having said this, comparison of diffusion and outgassing needs further investigation. However, I don't think outgassing like diffusion can be triggered by saturation. Some kind of pumping mechanism attributed to difference in surface layers (e.g. the creation of temporary vacuum layer) may trigger outgassing. In connection with climate change, ocean oxygen and carbon dioxide outgassing into the atmosphere are decreasing ocean oxygen and increasing atmospheric carbon dioxde. Both events have negative consequences. Decrease in ocean oxygen has impacted ocean plants and animals. So, outgassing if occurs within the ocean can be taken as a mixing process but if it throws out the molecules out of the ocean has negative consequences both for the ocean and atmosphere.

• Would you be able to address the question itself? As it stands it merely defines outgassing. See @naught101's comment underneath the question. – Isopycnal Oscillation Feb 18 '16 at 6:33
• It is a good question! But difficult to compare outgassing with diffusion and advection without data on those processes. It is a research question by itself, I think. – Gemechu Fanta Garuma Feb 19 '16 at 0:31