Acid Test: The Global Challenge of Ocean Acidification

[knocker]

This is six years old but it's still very much worth a look if you have a spare twenty minutes.

 

This groundbreaking NRDC documentary explores the startling phenomenon of ocean acidification, which may soon challenge marine life on a scale not seen for tens of millions of years. The film, featuring Sigourney Weaver, originally aired on Discovery Planet Green.

[Nick L]

Ocean acidification is probably the most tragic consequence of the crap we're pumping into the atmosphere. The impact on marine ecosystems could be catastrophic

[Styx]

Is carbon dioxide concentration at uniform levels in the ocean? Or is it possible that there are pools of higher concentration in areas, and where upwelling occurs or will occur, this will become obserable, meaning more severe consequences in certain parts of the ocean?

[Styx]

Actually I think that was a really daft question...

[Nick L]

Is carbon dioxide concentration at uniform levels in the ocean? Or is it possible that there are pools of higher concentration in areas, and where upwelling occurs or will occur, this will become obserable, meaning more severe consequences in certain parts of the ocean?

 

Weirdly I'm currently revising the carbon in the oceans section of my oceanography module

 

Generally, higher latitudes have higher concentrations of carbon dissolved in the ocean, as colder water can hold more carbon. As well as this, deeper water tends to hold more carbon.

[knocker]

Weirdly I'm currently revising the carbon in the oceans section of my oceanography module

 

Generally, higher latitudes have higher concentrations of carbon dissolved in the ocean, as colder water can hold more carbon. As well as this, deeper water tends to hold more carbon.

 

The marine carbonate cycle, as you know, is quite complicated and when I did an oceanography module some years ago now i bought a book, Oceanography by Summerhayes and Thorpe, which has an excellent chapter on it. Extremely interesting subject.

[knocker]

Briefly

 

The surface of the ocean undergoes gaseous exchange with the atmosphere. The direction of the exchange depends on the relative temperatures, and the difference in [C02], between the water and the overlying air mass. If the sea surface waters have a lower partial pressure of C0 2 than that in the atmosphere, then the gas moves from the atmosphere into the sea. This gaseous invasion continues until either the partial pressures equalise (the position of normal atmospheric equilibrium concentration, NAEC or the water mass sinks below the mixed layer before reaching equilibrium. The rates of invasion and escape (evasion) are influenced by meteorological conditions, surface waves and films, and contaminants in the sea surface. Diffusion of gases across the air-sea interface increases in stormy weather, and the dissolved gases are carried to deeper levels mainly by turbulent mixing. The seasonal or main thermocline that separates the upper and lower water columns provides an impediment to vertical mixing . The upper water column can freely exchange gases with the atmosphere. The equilibration steps involve a number of processes, mostly physical mixing of water masses, and some others, such as -diffusion across the air- sea interface and hydration of the gas, which are slow and possibly rate-determining.

 

Air-sea exchange tends to be a kinetically limited process compared to other processes that affect the partial pressure of C02 in the surface waters. The upper 100 m mixed layer of the ocean reaches equilibrium with the atmosphere in approximately one year. At high latitudes, warm water from the equator carried north by the oceanic circulation becomes under saturated in C02 upon cooling, and absorbs C02 from the atmosphere. The rate of invasion is enhanced through photosynthetic reduction of C02, especially in sub-polar waters, where nutrients are generally high and productivity is stimulated. It is therefore rare for surface waters to be at equilibrium with the atmosphere (Figure 12.11 ); equatorial waters tend to be supersaturated, and polar waters under saturated. Indeed, it is even possible to stimulate photosynthetic activity to increase the 'draw-down' of CO2.

 

Most of the C02 absorbed from the atmosphere is probably confined within the upper water column or mixed layer near the ocean surface. The limited mixing into deeper waters is the result of strong vertical stratification at high latitudes, where most of the anthropogenic C02 enters the ocean. The exceptions are the deep water formation areas that receive wind-borne C02• This process is likely to have absorbed only a small amount of anthropogenic C02 so far. There are clear differences in the atmospheric levels and seasonal trends in C02  between the hemispheres. The ‘draw down’ of CO2 by the ocean is limited  by wind patterns and is therefore probably confined to some sea areas only, and may be accentuated during certain periods of the year (such as during the winter when the upper water column is cooled and mixed to greater depths).

 

The capacity of the ocean to absorb CO2 is greatly augmented by the downward mixing and sinking of biogenic particulate organic matter (POM) and calcium carbonate into deeper waters. As a result of this 'biological pump', which moves carbon from surface waters to deep waters, the bottom waters contain so much C02 that they are supersaturated on average by about 30% relative to the NAEC. As the dissolved inorganic carbon (DJC) content of the oceans continues to rise, water masses that are supersaturated with CaC03 (e.g., calcite, aragonite, etc.) become under saturated then the CaC03 in the sediments begins to dissolve. A doubling of the present atmospheric C02 (g) concentration would increase the DIC by about 5-6%, and double the [H+] in surface waters (the effect would be smaller in deeper waters due to mixing). A possible consequence is that the production of calcite and aragonite by planktonic organisms in near-surface waters might be diminished as the water becomes less supersaturated - plankton communities may change.

 

Source.

 

Oceanography,  C.P. Summerhayes and S.A. Thorpe, Wiley

 

 

[Nick L]

Briefly

 

The surface of the ocean undergoes gaseous exchange with the atmosphere. The direction of the exchange depends on the relative temperatures, and the difference in [C02], between the water and the overlying air mass. If the sea surface waters have a lower partial pressure of C0 2 than that in the atmosphere, then the gas moves from the atmosphere into the sea. This gaseous invasion continues until either the partial pressures equalise (the position of normal atmospheric equilibrium concentration, NAEC or the water mass sinks below the mixed layer before reaching equilibrium. The rates of invasion and escape (evasion) are influenced by meteorological conditions, surface waves and films, and contaminants in the sea surface. Diffusion of gases across the air-sea interface increases in stormy weather, and the dissolved gases are carried to deeper levels mainly by turbulent mixing. The seasonal or main thermocline that separates the upper and lower water columns provides an impediment to vertical mixing . The upper water column can freely exchange gases with the atmosphere. The equilibration steps involve a number of processes, mostly physical mixing of water masses, and some others, such as -diffusion across the air- sea interface and hydration of the gas, which are slow and possibly rate-determining.

 

Air-sea exchange tends to be a kinetically limited process compared to other processes that affect the partial pressure of C02 in the surface waters. The upper 100 m mixed layer of the ocean reaches equilibrium with the atmosphere in approximately one year. At high latitudes, warm water from the equator carried north by the oceanic circulation becomes under saturated in C02 upon cooling, and absorbs C02 from the atmosphere. The rate of invasion is enhanced through photosynthetic reduction of C02, especially in sub-polar waters, where nutrients are generally high and productivity is stimulated. It is therefore rare for surface waters to be at equilibrium with the atmosphere (Figure 12.11 ); equatorial waters tend to be supersaturated, and polar waters under saturated. Indeed, it is even possible to stimulate photosynthetic activity to increase the 'draw-down' of CO2.

 

Most of the C02 absorbed from the atmosphere is probably confined within the upper water column or mixed layer near the ocean surface. The limited mixing into deeper waters is the result of strong vertical stratification at high latitudes, where most of the anthropogenic C02 enters the ocean. The exceptions are the deep water formation areas that receive wind-borne C02• This process is likely to have absorbed only a small amount of anthropogenic C02 so far. There are clear differences in the atmospheric levels and seasonal trends in C02  between the hemispheres. The ‘draw down’ of CO2 by the ocean is limited  by wind patterns and is therefore probably confined to some sea areas only, and may be accentuated during certain periods of the year (such as during the winter when the upper water column is cooled and mixed to greater depths).

 

The capacity of the ocean to absorb CO2 is greatly augmented by the downward mixing and sinking of biogenic particulate organic matter (POM) and calcium carbonate into deeper waters. As a result of this 'biological pump', which moves carbon from surface waters to deep waters, the bottom waters contain so much C02 that they are supersaturated on average by about 30% relative to the NAEC. As the dissolved inorganic carbon (DJC) content of the oceans continues to rise, water masses that are supersaturated with CaC03 (e.g., calcite, aragonite, etc.) become under saturated then the CaC03 in the sediments begins to dissolve. A doubling of the present atmospheric C02 (g) concentration would increase the DIC by about 5-6%, and double the [H+] in surface waters (the effect would be smaller in deeper waters due to mixing). A possible consequence is that the production of calcite and aragonite by planktonic organisms in near-surface waters might be diminished as the water becomes less supersaturated - plankton communities may change.

 

Source.

 

Oceanography,  C.P. Summerhayes and S.A. Thorpe, Wiley

 

It's as if you copied my lecture notes

[laserguy]

Generally, higher latitudes have higher concentrations of carbon dissolved in the ocean, as colder water can hold more carbon. As well as this, deeper water tends to hold more carbon.

 

Ok I'll try again, minus the sideswipe. There are no water-soluble allotropes of 'carbon'.

[Nick L]

Ok I'll try again, minus the sideswipe. There are no water-soluble allotropes of 'carbon'.

 

Ok, "dissolved" was the wrong word to use. Knocker has already described the process by which CO2 makes its way into the oceans, through the difference in partial pressures. Because the chemical reactions converting CO2 into other forms of carbon is so rapid, at present these partial pressures never really reach equilibrium. The result is that a significant chunk of our emissions get dumped into the oceans.

[knocker]

Ok, "dissolved" was the wrong word to use. Knocker has already described the process by which CO2 makes its way into the oceans, through the difference in partial pressures. Because the chemical reactions converting CO2 into other forms of carbon is so rapid, at present these partial pressures never really reach equilibrium. The result is that a significant chunk of our emissions get dumped into the oceans.

 

About 35% springs to mind.

[Nick L]

About 35% springs to mind.

 

Just reading through my notes, without the various carbon pumps in the ocean, atmospheric CO2 would be 3 times higher than we see now. With climate change, the ability of the oceans to take up this carbon will decrease. So this convenient dumping ground will become less viable. Warmer oceans can't take up as much carbon and the huge influx of CO2 will undoubtedly alter the chemistry of the oceans

 

As depressing as it was, my climate change module was very interesting.

[knocker]

Funny that they should just come up with this because removal of atmospheric CO₂ by iron enrichment thus stimulating phytoplankton growth was an idea tried out some years ago but later abandoned.

 

Study shows iron from melting ice sheets may help buffer global warming

 

http://www.eurekalert.org/pub_releases/2014-05/eaog-ssi051914.php

Edited May 21, 2014 by knocker

[knocker]

Open access to the above.

 

http://www.nature.com/ncomms/2014/140521/ncomms4929/full/ncomms4929.html

[Styx]

They have abandoned the ocean fertilizing experiments? Pity the concept was deemed unworthy to be investigated further, as it was envisaged a widespread program could have eliminated 30% of atmospheric emissions? Don't have a source for that figure I'm afraid, but I fleeted upon it last night, think it was reasonably recent. Naturally concerns of unintended consequences to marine ecosystems.  

Edited May 22, 2014 by Styx

[knocker]

They have abandoned the ocean fertilizing experiments? Pity the concept was deemed unworthy to be investigated further, as it was envisaged a widespread program could have eliminated 30% of atmospheric emissions? Don't have a source for that figure I'm afraid, but I fleeted upon it last night, think it was reasonably recent. Naturally concerns of unintended consequences to marine ecosystems.  

 

I may have been a bit hasty saying it's been abandoned completely but many technical problems have been encountered and the results of the various studies been very mixed. I can't really see it as a long term option. Even when it works and the sequested carbon sinks to the ocean floor it eventually returns to the atmosphere.