There is some dissolved CO2, as CO2, in seawater at the normal pH (around 8.1), and the solubility decreases with increasing temperature. So the acidity will decrease (the pH will rise) with an increase in temperature, if all else is constant. Pressure enters into this in a big way, as well, as it affects solubility of gasses. So it's only simple in the surface layer where you have the opportunity to establish equilibrium with atmospheric CO2.
Dissociation happens because it's free-energy favorable, so the extent to which it happens is determined by the free energy (delta-G). Recall that delta-G = RT ln(K). Take the derivative of K in terms of T and you'll see how the dissociation constant of HCO3 is affected by an increase in ocean temperatures.
I don't have a CRC Handbook of the proper age to look that Gibbs Free Energy up - but I'm going to bet that the change in solubility at real ocean temperatures overwhelms any thermodynamic terms anyway.
So, you don't even have to have more CO2 dissolved into the ocean to get greater acidity. All it takes is an increase in ocean surface temperatures.
More dissolved CO2 at constant temperature lowers the pH. Higher temperature at constant CO2 content lowers the pH. But solubility of CO2 in water drops by about 50% from 10C to 30C, so I still wonder if a rise in temperature - all alone - might actually raise surface pH.
Of course, when that surface water circulates down to the abyss where it's uniformly cold, the CO2 content will tell the tale. More = lower pH down there at the bottom.
It all depends on which factor carries the greatest weight in le Chateliers principle.....either greater dissolved CO2 or greater temperature affect on raising the disassociation constant. Greater surface temperatures dissolve less CO2 at the surface and greater surface temperatures change the point of equilibrium to greater disassociation of HCO3. An experiment could be done to find out how much CO2 would have to be dissolved in a liter of sea water to change the pH by 30%, which is the amount said to have occurred in the oceans since records have been kept. Another experiment could be done that raises the temperature of one liter of sea water by.7C, the amount of temperature gain in the same period of time, and see the change in pH. Calculations could then be done to see if temperature has more of an effect than CO2 in raising acidity levels.
It all depends on which factor carries the greatest weight in le Chateliers principle.....either greater dissolved CO2 or greater temperature affect on raising the disassociation constant.
Well, that's not going to be hard to figure out at a back-of-the-envelope level. A 50% change in solubility across a 20 degree difference is huge. Over the same temperature, though, the free energy will only change by about 6%. So the solubility is clearly your first-order factor.
I just figured that out for a change in temperature of .7C using the vant hoff equation. The resulting change in pH was miniscule compared to the supposed change of 30% in pH over the same period of time. Even though both disassociation reactions are endothermic, it takes a much greater change in temperature to change the pH by that much.
It is known that colder water can dissolve more carbon dioxide. The deep ocean is more acidic than the surface ocean because of that. The thermohaline circulation brings cold deep water to the surface at certain points. If that upwelling occurs at a steady pace over time, then the extra acidity it brings to the surface cannot be taken into consideration when considering causes of increased ocean acidity. However, if that upwelling occurs at a faster past than normal,an increase in ocean acidity can logically be blamed on it. Scientists claim that an increase in ocean surface temperatures can speed up the thermohaline circulation. If ocean surface temperatures are not rising due to an increased greenhouse effect but due to other causes, an increase in ocean acidity can be blamed on the thermohaline circulation instead of increased carbon dioxide being dissolved.
I am currently almost through with a course in mineralogy. I am having trouble consistently telling the difference between quartz and nepheline and alkaline feldspar that lack obvious twinning. I am also having trouble telling the difference between biotite and hornblende especially when the biotite is very weathered. I am talking about thin sections for these minerals and not hand sample specimens of them.
It's been a while since I've looked at thin sections, but what I remember is that quartz is often anhedral, black/white, and clear with no fractures. You can often find small inclusions of other minerals as well as tiny fluid inclusions, and they are often aligned. When deformed, quartz often displays undulatory extinction, sometimes having a granular appearance.
Unless they are interstitial, the feldspars often have twinning and are subhedral to euhedral. And if I remember correctly, cleavage planes are more common and visible, and since feldspars will alter to clay fairly easily, you will often see some sort of 'texture' to the feldspars, particularly along cleavage planes. Fluid inclusions are less common.
Play with the light source. Sometimes you can see cleavages and regular fracture patterns with the feldspars, whereas the quartz will remain smooth.
What I remember about biotite is the brown color (in plane light), the feathery/splintery ends, and bird's eye extinction. Bird's eye extinction is a 'rough' or mottled appearance. I believe this is because the biotite is made up of tiny plates of biotite and when bent up/broken, will go extinct at different angles.
Hornblende, on the other side, often has clean, straight edges (unless being replaced by biotite), is often euhedral/subhedral, and has visible 120/60 degree cleavage, visible as fractures.