Why Does the CaCO3 Compensation Process in Ocean Acidification Work So Slowly?

[Absalon]

Hi. I've been doing some reading about ocean acidification lately, and there is one concept that I don't understand, and that I can't find a good explanation for. This is a good forum, and I hoped that you could help me.

When I read about ocean acidification on Real Climate's post on this topic they say:
"The natural pH of the ocean is determined by a need to balance the deposition and burial of CaCO3 on the sea floor against the influx of Ca2+ and CO32- into the ocean from dissolving rocks on land, called weathering. These processes stabilize the pH of the ocean, by a mechanism called CaCO3 compensation. CaCO3 compensation works on time scales of thousands of years or so."

http://www.realclimate.org/index.ph...em-with-cosub2sub-emission/langswitch_lang/wp

I understand that this is a critical point about the whole process, which you need to consider to understand how fast and massive release of CO2 will make the oceans more acid, while slow and massive release (like what have in the past) don't need to create the same effect.

But I do not understand WHY the CaCO3 compensation works so slowly. Can anyone help me by explaining this, or direct me to a good informative site?

Oh, and: The RealClimate post is based on this research: Caldeira, K., and Wickett, M.E. Anthropogenic carbon and ocean pH. Nature: 425, 365, 2003.

 

[chriscolose]

I'm not a big chemistry person so I'd like to just refer you to a few sources from David Archer which should help you in getting an answer. It's been a while since I went over these papers, and my knowledge of the ocean acidification chemistry is somewhat shaky, but here you go:

http://geosci.uchicago.edu/~archer/reprints/archer.1998.neut_long.pdf

http://geosci.uchicago.edu/~archer/reprints/archer.2005.fate_co2.pdf

 

[Huyen401]

Hi there! First of all, I want to commend you for doing your own research and trying to understand the concept of ocean acidification. It's a complex topic, but with some explanation, it can become clearer.

To answer your question, let's break down the concept of CaCO3 compensation. As the Real Climate post mentions, the natural pH of the ocean is determined by a balance between the deposition and burial of CaCO3 on the sea floor and the influx of Ca2+ and CO32- from dissolving rocks on land. Essentially, this means that the ocean has a natural way of regulating its pH levels by storing excess calcium and carbonate ions in the form of CaCO3 (calcium carbonate) on the sea floor.

Now, when we release large amounts of CO2 into the atmosphere, a significant portion of it is absorbed by the ocean. This excess CO2 reacts with water to form carbonic acid, which then dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). This increase in hydrogen ions leads to a decrease in pH, making the ocean more acidic.

To counter this acidification, the ocean tries to restore its natural pH balance by using up the excess hydrogen ions through a process called CaCO3 compensation. This involves dissolving CaCO3 from the sea floor to neutralize the excess hydrogen ions and bring the pH back to its natural level. However, this process is slow because it takes time for the CaCO3 to dissolve and for the neutralization to occur.

Furthermore, the amount of CaCO3 available for this compensation process is limited, and it takes thousands of years for new CaCO3 to be deposited on the sea floor. This is why the CaCO3 compensation process works on a slow timescale of thousands of years.

I hope this explanation helps to clarify why the CaCO3 compensation process works slowly. If you want to learn more about ocean acidification, I would recommend checking out the National Oceanic and Atmospheric Administration (NOAA) website or the Ocean Acidification International Coordination Centre (OA-ICC) website for more information. Hope this helps!