Global warming, ocean acidification and mass extinctions

On-going anthropogenic carbon emissions has reached levels 40% higher than pre-industrial ones in 1750, due to human burning of fossil fuels. Despite international discussions and various national efforts to decrease carbon emissions, the amount of heat-trapping carbon dioxide in the atmosphere reached a record 390.9 parts per million (ppm) in 2011, according to a report recently released by the UN’s World Meteorological Organization (WMO). As a result, 30% more  atmospheric heat was kept from escaping to space than in 1990. The increased amounts of CO2 in the atmosphere has lead to a 1°C increase in average temperatures worldwide. This may not sound much, but with the long retention time of CO2 in the atmosphere the average temperature will continue to rise for a long time even if we should manage to limit our carbon emissions extensively. The World bank estimates an average temperature rise to as much as 4°C by 2060 unless we start reducing our carbon emissions significantly! The effects of such a dramatic global warming would mean serious threats to the human civilization, with extreme weather, heat waves and sea-level rise, but that is not all…

The geological record testifies to the effects of global warming. Numerous scientific articles dealing with the causes and consequences of the mass extinctions at the end-Permian (252 million years ago) and end-Triassic (201 million years ago) have provided evidence of the dire effects of intense global warming. Both events are linked to massive volcanism from large igneous provinces (LIPs) that emitted huge amounts of CO2 and methane to the Earth’s atmosphere. As discussed by Payne and Clapham (Annual Review of Earth and Planetary Sciences, May 2012) such mass extinction events in the geological record may serve as an important ancient analog for the twenty-first century! Climate change and increased temperatures, possibly coupled with destruction of the ozone layer, can account for the extinctions on land, whereas changes in ocean oxygen levels, CO₂, ocean acidification, and temperature made life difficult for marine animals, resulting in the demise of as much as 96% and 80% of all species for the end-Permian and end-Triassic events, respectively.

Recent scientific reports provide warning signals. One of the most well documented consequences of the increased CO2-levels at the end-Permian and end-Triassic events is referred to as the biocalcification crisis. The increased CO2-levels caused upper ocean acidification due to lowering of the pH of surface waters, causing problems for calcareous organisms such as calcareous phytoplankton and reef-building organisms, e.g. bivalves and corals. Scientists have long discussed the on-going coral bleeching as one result of our anthropogenic carbon emissions, but now Bednarsek et al. (Nature Geoscience, advanced on-line publication 2012) report alarming evidence of dissolution of shells on living pteropods (shell-bearing free-swimming sea-snails) in the Southern Ocean, providing further warning signals of on-going ocean acidification.

In addition, Arneborg et al. (Nature Geoscience, advanced on-line publication 2012) show increased inflow of warm and salty bottom waters to the central Amundsen shelf in Antarctica where the thinning of glaciers have persisted over the last decades. The Amundsen shelf is part of the West Antarctic Ice Sheet that contains enough ice to raise global sea level by several metres and, because it is grounded mainly below sea level, it is extra sensitive to ocean warming.

These reports, among many others, should serve as serious warning signals to world leaders that we need to take immediate action to reduce carbon emissions. So far, we have not managed to act efficiently on reducing emissions. At the UN-sponsored climate meeting in Copenhagen in 2009 the relatively weak agreement was to a non-binding target of limiting the world’s greenhouse-gas-triggered temperature increase to no more than 2°C (3.6°F) above preindustrial levels to limit the potential damage. The 2011 numbers provided by  the UN’s World Meteorological Organization (WMO) clearly show that we are failing to keep even that!

Large herbivorous dinosaurs sustained Mesozoic greenhouse climate through flatulence?

In our society today we are very much aware of the effects of greenhouse gases on the climate. Global warming due to anthropogenic pollution has been discussed vigorously over the last decade. We spend enormous amounts of money on research and development of Carbon Capture and Storage, i.e. the possibilities of storing excess carbondioxide underground.

Geologists discuss the causes and effects massive release of carbondioxide or the four times more potent greenhouse gas methane possibly had on the climate and on life on Earth during the end-Permian and end-Triassic mass extinction events.

In a quest to find out what is normal and not normal when it comes to carbondioxide levels in the atmosphere, and the circulation of carbon on Earth, researchers have found out that our domestic cows produce some 50-100 million tonnes methane per year by gases formed in their guts.

Sheep are also environmental bad guys… 😉

Now a team of researchers lead by David Wilkinson have calculated how much methane may have been produced by large herbivorous dinosaurs, the so called sauropods including e.g. Apatosaurus, and their best estimates suggest 520 million tonnes of methane per year. A truly staggering amount as this equals the total combined methane emissions per year from all sources on Earth, i.e. from all animals and all human activities. 

     Sauropods probably had big guts containing lots of methane producing microbes!

The mean global temperature during the Mesozoic is estimated to have been 10 degrees Celsius warmer than today. Interestingly the Jurassic and Cretaceous periods are in general considered to have been periods of high diversity and productivity, both at sea and on land, despite the high levels of carbondioxide in the atmosphere.

So how come we fear carbondioxide and methane emissions today?

The key issue is probably time. Our planet; its interacting animals and plants, minerals and rocks, needs time to adapt to environmental changes. Fast injection of huge amounts of greenhouse gases to the atmosphere, whether from massive volcanism or from anthropogenic emissions, can shift climatic zones and cause major disruptions in ecosystems.

Perhaps the methane farts from the herbivorous dinosaur populations only sustained the greenhouse climate that was initiated at the end-Triassic?

Perhaps they didn’t really make things worse…just kept things normal?

The less spectacular period boundary of the Mesozoic…

I guess most people interested in geology and the history of life on Earth have heard about the dramatic period boundaries of the Mesozoic.

The most well known is of course the upper boundary of the Mesozoic, the Cretaceous-Paleogene boundary which marks the demise of the dinosaurs ca 65 million years ago. This boundary is marked not only by a catastrophic extraterrestrial impact, but is also contemporaneous to massive volcanism (Deccan Traps in India) and subsequent climatic and environmental  changes of these events.

Almost equally famous and marked by an even bigger mass extinction is the lower boundary of the Mesozoic, the Permian-Triassic boundary ca 251 million years ago, associated with the end-Permian mass extinction event when ca 95% of all life died out. The end-Permian event is linked to massive volcanism in Siberia and the longterm climatic and environmental consequences where so severe that the major part of the Triassic is characterised by a harsh arid hothouse climate.

Some have probably also heard of the Triassic-Jurassic boundary, ca 201 million years ago, also associated with a major mass extinction event linked to the perhaps largest large igneous province known, the Central Atlantic Magmatic Province – massive volcanism during the initial opening of the Central Atlantic – with severe climatic and environmental consequences.

Am I repeating myself? 😉

But how many have heard of the Jurassic-Cretaceous boundary ca 145 million years ago?

This less well-known period boundary is also marked by major climatic changes. At least on the northern Hemisphere. Palynological, sedimentological and geochemical studies bear witness of climatic change from predominantly arid to semi arid conditions in the latest Jurassic to more amicable humid conditions in the earliest Cretaceous of NW Europe (see e.g. our paper Lindström and Erlström, 2011 for references).

So far, this less spectacular period boundary has not been linked to any major volcanic events or extra terrestrial impacts. And now Valentin Fischer and his colleagues have published a study in PLoS ONE (read paper here) about one specific ischtyosaur that survived the less famous Jurassic-Cretaceous (J/K) mass extinction and in fact their study suggests that the J/K event hardly affected ischtyosaurs at all 😀

Volcanoes are not only destructive destroyers!

Some of the most severe crises in the history of life on Earth are linked to massive volcanic events, so called Large Igneous Provinces or LIPs. For the most severe mass-extinction, the end-Permian event ~250 million years ago, the LIP involved is the Siberian Traps, while the end-Triassic event (~200 million yeasr ago) is linked to the Central Atlantic Magmatic Province or CAMP. Even the most well-known mass-extinction event, that which saw the demise of the dinosaurs at the Cretaceous-Paleogene boundary ~65 million years ago, is temporally linked to a LIP, namely the Deccan Traps in India. Although for the latter event, it is uncertain if we will ever be able to separate the effects of the Deccan Traps on life on Earth from the effects of the extraterrestrial Chixculub impact.

Even so, we are used to look upon volcanic activity as something devastating. Many are the historical reports of death and destruction by volcanic forces: the 1650 BC eruption of Santorini (Thera) in Greece which probably wiped out the Minoan culture, the famous Vesuvius eruption (Italy) in 79 AD which wiped out the Roman cities Pompeji and Herculaneum, or the 1815 AD eruption of Tambora in Indonesia which killed more than 83.000 Indonesians and changed the climate for years to come.

The famous Indonesian volcano Krakatoa had a massive eruption in 1883 releasing 200 megatons of energy!

But geologically speaking volcanoes helped build the land that we live on, and still do. The destructive forces are also constructive, adding new land where nothing was before. Like the new island, formed by volcanic activity in the Red Sea just off the coast of Yemen in December 2011. New crust formed in the Red Sea Rift, where Africa separates from the Arabian Plate…

Check out the images of the new island here!

Katla is rumbling

Iceland’s biggest volcano, Katla, is rumbling. During the last month there have been more than 500 tremours in and around the caldera. Reaching 1512 m a.s.l. the 10 km wide caldera poses a more severe threat than the recent eruptions of Grimsvötn (May 2011) and Eyjafjallajökull (March 2010), where especially the latter caused major disruptions in the air traffic over northern Europe. 

The caldera is partly capped by a glacier. If Katla erupts melting glacier ice could cause flash mudflows. Volcanic ash from Katla also have the potential of reaching higher up in the atmosphere, casing devastation not only on Iceland.

In 1783 the Laki fissure eruptions, located within the same volcanic zone as Katla, erupted continuously for 8 months. A minor version of the floodbasalt volcanism typical of large igneous provinces, the Laki fissure released huge amounts of ash, hydroflouric acid and sulfuric acid (Stephenson et al., 2003), causing massive destruction on Iceland, where every fifth islander and half of the livestock were killed.

The Laki volcanic fissure on Iceland. Original photo on http:// marsoweb.nas.nasa.gov/ HiRISE/science_themes/volcanology.html

But the devastation reached farther than that. A sulfuric ash cloud from the eruption was distributed over the northern Hemisphere. Historical records from France and England report severe health issues for both people and animals, as well as misgrowth of crops and fruit. In the aftermath of the atmospheric pollution from the Laki eruptions, colder climate and increased mortality plagued Europe for a decade (Grattan, 2005).

Historical records show that Katla usually erupts every 40-80 years. The last major eruption was in 1918. Volcanologists are worried because they are not sure what to expect. Volcanoes are unpredictable and the impact of an eruption depends largely on its size, volume, ash composition and climatic conditions.

 Read more on Sky news and BBC news

Mercury new culprit in end-Permian event?

In a new paper in Geology Sanei et al. (abstract) address the potential impact of mercury loading from the Siberian Traps during the end-Permian event. Mercury is one of the most toxic elements on our planet, and one that cause much concern from an environmental perspective seing as it is very persistent and has long-ranging impact on biota.

Coupling new mercury data with their previously published carbon-isotope and coal-fly-ash events in the Permian-Triassic boundary succession of the Sverdrup Basin (Grasby et al., 2011) they propose that suppressed organic productivity due to deteriorating environmental conditions in the basin lead to catastrophic build-up of dissolved mercury in the sea.

The excess dissolved mercury could not be removed until conditions turned extreme euxinic and sulfide-mercury drawdown commenced.

It will be interesting to see if mercury-toxicity events are associated with other major volcanic events in Earth’s history!