Tag Archives: CO2

Mineralogy of carbonates; basic geochemistry

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Tabulation of the important equilibria in the carbonic acid - carbonate system

Some basic geochemistry of carbonates, carbonic acid and carbon dioxide

This is part of the of  How To…series…  on carbonate rocks

Sedimentary carbonate petrology is concerned first and foremost with the precipitation and dissolution of mineral phases; principally calcite, aragonite and dolomite. Both processes involve chemical reactions and the two primary requirements for these reactions are:

  • thermodynamics – there needs to be sufficient energy to drive the reactions, and
  • an excess or deficit of dissolved mass that, for the minerals of interest, includes  Ca2+(aq), Mg2+(aq), and CO32-(aq) (aq = aqueous)

All sedimentary carbonate reactions at the surface or during sediment burial take place in water: fresh water, sea water, or concentrated brines. Furthermore, the chemical composition of these fluids can evolve, for example during burial (sea water to brine), or uplift and exposure (sea water to fresh meteoric water). Such changes are commonly manifested as cement stratigraphy (e.g. high-Mg calcite overlain by low-Mg calcite), or where clasts, matrix and early cements are replaced by new generations of calcite or dolomite.

Evolution of cements and fluid chemistry in a cool-water limestone, NZ.

We are also interested in carbonate reactions because of the present trend towards climate change and the possibility that ocean chemistry may change; ocean acidification tops the list here. To get beyond the hyperbole, to determine whether this is a real possibility or not, we need to understand some basic chemistry.  Some introductory concepts are outlined herein.

To delve deeper into the complexities of the carbonate system, have a read of the contributions cited below. Continue reading

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So, adding CO2 does increase surface heating; how science has filled another gap in our knowledge

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Read any scientific paper or blog on climate and you’re bound to come across the phrase radiative forcing.  Radiative forcing is central to all climate science. Radiation from the sun heats our atmosphere and earth surface.  Some of this radiation is reflected back to space. If there is a balance between incoming and outgoing radiation then average global atmospheric temperatures neither increase or decrease. However, if the balance is perturbed, climate will warm or cool. Radiative forcing causes climate imbalances.  Thus, volcanic aerosols tend to cool things off, decreasing albedo will tend to warm them. Continue reading

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The Bubbles That Changed our Perspective on the World’s Climate

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Camp water supply from a small pond on this iceberg

One of my geology field seasons in the Canadian Arctic worked out of a base-camp on Axel Heiberg Island (west of and snuggled against Ellesmere Island).  It was the spring thaw and all rivers and streams were muddy.  Our only source of clean water turned out to be a small melt-water pond atop an iceberg in Strand Fiord, a few hundred metres offshore.  The helicopter would make daily trips with a 45-gallon drum to collect the water.  The ice and its water were crystal clear and probably a few thousand years old. It was a treat. Perhaps the only thing missing was the occasional Scotch or G&T. Continue reading

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Out of Sight but no longer out of mind; Hidden sources of carbon dioxide and methane

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Emma Fiord, 1987, with lots of sea ice

With the general emphasis on carbon emissions from fossil fuels and the ensuing discussions on climate change, we tend to forget some of the natural sources of greenhouse gases that continually leak carbon dioxide (CO2) and methane (CH4) into the oceans and atmosphere.  Two such sources are gas hydrates beneath the sea floor and permafrost.  Both sequester carbon, but the sequestration is rather tenuous; both can easily be disturbed by natural and anthropogenic processes.

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