5. Barium's Mystery Associations

Barium (Ba) is a typical rare Group 2 element in the periodic table. It is rare and therefore very low in abundance. It's most commonly found as the mineral Barite and this is what it looks like: 

Barite

The flux of Ba_biogenic has been shown to have a reasonably good correlation with carbon export in the modern ocean to the sea floor. The graph below shows a nice association with Barium and the δ¹³C and δ¹⁸O across the PETM. 

Bains et al., 2000

The key mineral used in these measurements is Barite. The exact mechanism for its biogenic origin is still largely debated, however it is though to form in the surface waters of the ocean in microenvironments associated with decomposing organic matter - such as foraminifera. The mass accumulation rates over the PETM appear to show a positive shift in response to carbon cycle and climate changes. That is to say, more Barite was being deposited in the sediments at this time. But what does this mean?

More Ba_biogenic in the sediments implies that more organic matter was being produced in the surface waters, so the Barite rain became more intense. Unlike the coverage of our current climate crisis, the PETM appeared to do well for surface water species. Scientists have linked this to other phenomena observed at the time which include: 

• increased continental run off providing nutrients Nitrogen, Potassium and Phosphorous, which limit productivity in the modern oceans.
• increased volcanism, particularly in the North Atlantic, further increased ocean fertilisation
• rising global temperature by 5-7°C and increased CO₂ concentrations by 2000Gt. These are known to increase the rate of photosynthesis in modern plants

Other research has linked the Barite shift to the release of methane. As we have discovered before the methane in hydrates is created by microorganisms that live in the sediment. It has been noted in this research that Barite had a mass balance problem in previous studies - i.e. there was too much Barite in the sediments for this to be caused by productivity. In a bitter sting back, the supporters of the biogenic Barite explained that their cores had come from the continental shelves of the oceans - areas of high productivity, with dynamic equilibria associated with carbon fluxes and organic-carbon burial due. Basically, the continental shelves are very productive regions because, in part, due to their proximity to the continents and the run-off they receive. 

What the biogenic Barite theory also shows is a feedback mechanism. An increase in productivity acts as a counter-process to the release of methane to reduce the levels of greenhouse gases. It has been calculated that, globally, this could have been achieved in 60 000 years. This is critical today when our climate is changing faster than it has ever done so in the history of the planet. I guess it provides an unnerving reassurance that there is a possibility that everything will sort itself out. But, I ask, at what cost?