Tuesday, November 16, 2010

Sharpening the tools in the carbon dioxide garden shed

This weeks Smith Lecturer is Barbel Honisch, a tenure-track geochemist at Lamont-Doherty Earth Observatory (Columbia University). Lamont is center for research on Earth and ocean processes with a strong emphasis on climate. Like last weeks speaker Honisch is both German (which is irrelevant) and interested in reconstructing past ocean pH and atmospheric CO2 levels. Honisch was initially trained as a marine biologist, so she approaches ocean history questions with biological in mind. She is specifically interested in using boron isotopes as an indicator of past seawater pH. To check if calcium carbonate organisms are recording the pH of the seawater they float in correctly, Honisch has grown these organisms (foraminifera) in the lab.

Boron isotopes in marine carbonates have the potential to provide us with information about past ocean carbonate chemistry, as the boron isotopic composition of marine carbonates is primarily controlled by the pH of seawater. The boron isotope paleoacidity indicator is that the uncharged species B(OH)3 is enriched in 11B by 20% over the charged species B(OH)4-. As the fraction of boron changes with pH, so must the isotope.

11B(OH)3 + 10B(OH)4- double arrow 10B(OH)3 + 11B(OH)4-

Boron isotopes alone provide us with only one parameter (i.e. pH) of the marine carbonate system. For accurately translating boron isotope data into pH values and subsequently for calculating other parameters of the carbonate system such as aqueous PCO2, we need additional information on temperature, salinity and a second carbonate parameter such as carbonate ion concentration or alkalinity (the amount of carbonate ion).

Logic diagram shows how seawater pH (on the left) influences the ratio of stable isotopes of boron in corals that grew in that water (on the right). From Chacko (2009)
Application of the boron isotope pH proxy to the late Pleistocene ice ages has led to a convincing estimation of surface ocean pH that can be compared to atmospheric pCO2 as recorded in ice cores. Now Honisch is in the process of extending the pH and pCO2 reconstructions beyond the reach of ice records, into the Cenozoic era. The first application beyond the reach of ice core CO2 measurements focused on the mid-Pleistocene transition when the ice ages became significantly longer in length and duration. Her results suggest that although CO2 and climate were tightly coupled, the climate transition was not driven by an overall decrease in atmospheric CO2 that could have cooled the planet.

Video about growing 'pets' that will tell you about climate change through time.


  1. Today's lecture seemed considerably more graphics heavy than other previous ones, which actually made it a little harder to follow. The graphic were rather intense and I would have liked to have had a little bit more time to soak everything in and logic out what the graphs were trying to represent. While it is nice that Barbel didn't get bogged down on any point, she seemed to just speed through most of her research. I am glad that the question was asked that she draw some conclusions from her final slide and say what can, and what can not, be derived from her work.

  2. Since chemistry is my weak point, today's lecture's focus on Boron made it slightly difficult for me to keep up with Barbel's lecture. However, her guidance in what we should anticipate helped in comprehension.

    I think this lecture had perfect timing since it somewhat picked where last week's left off.

  3. The past two weeks I have enjoyed speaking with the lecturers prior to their talks. I think it has helped focus all of the information and explain the topics presented.

    Although logical, it is still very interesting that so much information is gained from the ice cores. It seems like it would be hard to keep the ice from being contaminated. Because ice melts easily it seems like there would be a lot of contamination from the melted water mixing with layers that are still frozen. I don't know anything about how they keep this from happening, but it seems like a large problem to overcome to get accurate, reliable data.

  4. I agree with Megan. Talking to the speakers prior to the lecture was a great introduction to the subject matter. Especially since they are obviously well versed in the area it is easy for them to explain something in easier terms than any scientific paper we read prior could.