On November 11, 2015 there will be a meeting entitled “Puzzle of Earth’s Uninterrupted Habitability” to be held at the Geological Society of London (GSL). This meeting will have a strong emphasis on Gaia theory and several prominent Gaian scholars will be speaking, including Tim Lenton, David Wilkinson, Toby Tyrrell, and David Schwartzman. As a Fellow of the GSL I have been invited to speak at this meeting. Here are the title and abstract of my talk:
“Biological mediation of acidity and alkalinity: Does habitability require regulation of environmental pH?”
Lee Klinger, Independent Scientist, Big Sur, CA USA
Abstract – Climatic cycles such as ice ages represent large excursions in global temperatures and are associated with significant changes in atmospheric CO2, non-sea salt sulfate, and dust, as recorded in ice cores. Ice age excursions in the pH of marine waters are predicted to result from the altered concentrations of CO2 in those waters. In addition, there are a number of biologically mediated processes affecting the pH of terrestrial and marine environments.
During interglacials terrestrial ecosystems are dominated by forests and grasslands that experience frequent disturbances, especially fire, which tends to alkalinize the soils. At the onset of glaciation higher latitude fire regimes subside and the forests become podzolized, with a corresponding decrease in soil pH. Many of these areas are eventually paludified, owing primarily to the acidifying and swamping effects of mosses and lichens, which eventually dominate the expanding peatlands. Mosses and lichens are known to stimulate silicate weathering rates to levels that could significantly reduce atmospheric CO2, and the cooling effects of peatlands are thought to play a role in ice age initiation. There is evidence that the production of iron-rich organic acids by peatlands greatly enhances phytoplankton blooms in adjacent coastal areas. Rainfall chemistry from the Pacific northwest points to the occurrence of biogenic acid rain likely originating from DMS and other biogenic sulfur compounds emitted by the phytoplankton. A feedback results through the nss-sulfate deposition enhancing the growth of mosses.
As ice ages progress and glaciers grow, dust levels in the atmosphere are also seen to rise. Much of this dust is due to an increase in glacial loess. The iron content of the dust stimulates marine productivity in open ocean areas. Oceanic inputs of iron from volcanic ash and glacial outwash are also seen to increase during glacial periods.
The culmination of the glacial period is defined by feedbacks involving the expansion of glaciers into areas formerly occupied by peatlands. The high mineral content of the glacial loess, along with episodes of volcanic ash would tend to alkalinize the terrestrial ecosystems and discourage the proliferation of mosses and other acidifying organisms.
Thus, the pH excursions in the ice age cycle may be related to the biogeochemical coupling of the iron and sulfur cycles. This coupling could have its roots in the Precambrian banded iron formations (BIFs), cyclic depositions of iron-rich minerals that are likely biogenic in origin. BIFs are seen to be closely associated with snowball earth conditions.