[Coral-List] High pCO2 and calcification in the far distant past

[Sam Kahng]

Hi John,
 
I just taught a section on this to my bio ocn students. Kump et al. (2009) is a good introductory reference for the casual reader, however a basic understanding of carbonate chemistry is required. On geological time scales (greater than residence time of ocean basins), high atm CO2 is generally associated with high ocean alkalinity (TA) and proliific coral reef accretion. The high atm pCO2 causes accelerated terrestrial rock weathering (basalts and carbonates) which floods the oceans with HCO (raising alkalinity despite high atm pCO2). The disconnect with the modern scenario (short-term imbalance) is that weathering feedback and ocean mixing/equilibration takes a long time. There are many good references that discuss the Paleocene-Eocene Thermal Maximum (PETM) whiich was the most recent "rapid" ocean acidification/carbonation event. Its initial and long-term effects on marine carbonate deposition are fairly well documented by geochemists. 
  
Kump LR, Bralower TJ, Ridgwell A (2009) Ocean acidification in deep time. Oceanography 22:94-107
 
Aloha, Sam
 
 
> Date: Wed, 1 Jun 2011 11:11:26 -0400
> From: jware at erols.com
> To: coral-list at coral.aoml.noaa.gov
> Subject: [Coral-List] High pCO2 and calcification in the far distant past
> 
> Dear List:
> 
> For a long time I have thought, as many of you have, that paleo records 
> of times with high pCO2 would be good analogs for the future effects of 
> high pCO2 on present coral reefs. Unfortunately, I have not found a 
> good reference that looks at available data and then discusses the 
> results in an understandable format. I had thought that the following 
> reference was going to be helpful:
> 
> Doney,SC; Fabry,VJ; Feely,RA; Kleypas,JA (2009): Ocean acidification: 
> the other CO2 problem. Annu. Rev. Mar. Sci. 1, 69-92.
> 
> Unfortunately, this is what I found in that reference: "Periods of high 
> pCO2 (Permian, Cret) exhibit massive shallow-water CaCO3 deposits. 
> Initially this appears to be a conundrum. The short answer is that 
> saturation states may have been high during these periods despite high 
> pCO2. The long answer is complicated." 
> 
> While the above may not be a fully accurate quote, it carries the 
> intent. My problem is that the long and complicated answer is not 
> given. Can anybody out there provide a reference that explains high 
> calcification rates the the far past when (presumably) there were 
> periods of high atmospheric pCO2 but also high calcification rates.
> 
> I note that some authors claim that pCO2 in the Cretaceous could have 
> been in the 1000s (ppmv), and I also realize that the major calcifiers 
> in the late Cretaceous were probably rudists (sort of clams) not corals. 
> But what is out there that I have missed?
> 
> John
> 
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