Posted by: A Siegel

Previous Warming Periods May Have Caused Mass Extinctions

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Keywords: Climate, forests

This guest post from scientist FishOutOfWater looks at the what might be the closest event in Earth’s history to what humanity, through its ever mounting carbon emissions, is rapidly heading the planet to …

The most precise study yet of the the earth’s most catastrophic extinction event, the end Permian, found that warming caused by natural releases of CO2 was greatly amplified by the collapse of tropical and temperate forest ecosystems which then caught fire releasing huge stores of carbon sequestered by trees. So much light 12Carbon came from burning and dying trees that the CO2 in air was significantly lighter for 20,000 years.

The extinction interval was less than 200,000 years, and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.

This stunning report, by a team of MIT and Chinese scientists was published on-line today in Science magazine. So much carbon was released by this chain of events that the oceans became acidic, leading to the greatest mass extinction of marine species ever. According to the detailed chronology of this study fires ignited by volcanic eruptions contacting large deposits of coal and oil shale caused a chain of catastrophes. The drying and burning of the earth’s forests caused by the climate change brought on by the increased levels of greenhouse gases, led to catastrophic soil loss. The oxygen levels of the ocean and atmosphere dropped. Sulfurous gas levels rose. The combination of so many rapid disastrous changes caused the greatest extinction event in earth’s history.

Middle Permian tropical scene, artist’s interpretation

Over the past decade the Amazon has gone through two 100 year droughts, causing massive tree mortality and subsequent spikes in atmospheric CO2 levels. Until the last decade, humid conditions tended to suppress Amazon fires. Recent reports show that increases in tropical Atlantic sea surface temperatures tend to trigger Amazon droughts. A report published in June, 2011 showed that fire severity could be predicted based on correlations with tropical Atlantic sea surface temperatures

Using meteorological stations precipitation and the Moderate Resolution Spectroradiometer (MODIS) Active-Fires (AF) during 2000–2009, we show that fire anomalies vary closely with July-August-September (JAS) precipitation variability as measured by the Standardized Precipitation Index (SPI). The precipitation variability is, in turn, greatly determined by sea surface temperature (SST) anomalies in the North Tropical Atlantic (NTA). We develop a linear regression model to relate local fire activity to an index of the NTA-SST.

The Amazon is becoming susceptible today to warming, drying, death and fires like the tropical forests were 250 million years ago at the end of the Permian. The death spiral that happened at the end of the Permian is shocking to read about. This is a history we must study and learn so we don’t repeat it.


Fig. 5. Scanning electron micrographs of charcoal and carbon micro-particles from the PTB beds in South China. (A) transverse view of a fragment of charcoal from Guanbachong showing homogenized cell walls and three-dimensional cellular preservation with open lumina. (B) showing pitted tracheid with spiral lines, from Guanbachong. (C) from the Clarkina meishanensis Zone just below the PTB at the Tieqiao section in Laibin, Guangxi Province. (D) showing homogenization of cell walls, pitted tracheid and brittle fracture from Chuanyan section. (E) Carbon particle from Bed 25 at Meishan C section. White bars=20?m.

Biomarker and organic carbon isotopic studies are consistent with widespread continental weathering and transport of plant fragments and black carbon from wildfires, related to collapse and burning of terrestrial plants (27, 30, 34). The correlations between marine, marine-terrestrial transitional, and terrestrial sections (Fig. 4) indicate that the marine extinction was synchronous across South China at the <0.2 Myr level with loss of the rainforest, wildfires and the cessation of coal formation (24, 26). Integrated biomarker and organic C isotopic studies also indicate perturbations to the carbon cycle characterized by increased terrestrial weathering during and immediately after the collapse of terrestrial ecosystem and widespread introduction of sulfidic waters into the photic zone (1, 12, 33) as indicated by the concentration of pyrite within the extinction horizon and cyanobacterial expansion (13).Despite evidence for dysoxic and anoxic conditions in the deep ocean both just before and after the extinction (2, 3), the synchroneity of Ccarb isotope excursion and extinction suggest a causal link between the introduction of the light carbon and the extinction. The simplest way to produce a widespread, large pulse of shallow water anoxia and euxinia is by carbon dioxide and/or methane-induced global warming that leads to decreased oxygen solubility, intensification of continental weathering, and increased nutrient delivery to the oceans [e.g., (33)] with biodiversity decline coinciding with onset of a period of rapid warming.

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December 24, 2011

A guest says:

I spoke to someone I volunteered at a dinosaur dig who said they though the permian extinction may have been caused by anoxia.

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