GeoLog

Biogeosciences

GeoTalk: How hydrothermal gases change soil biology

The biosphere is an incredible thing – whether you’re looking at it through the eye of a satellite and admiring the Amazon’s vast green landscape, or looking at Earth’s surface much more closely and watching the life that blossoms on scales the naked eye might never see, you are sure to be inspired. Geochemist, Antonina Lisa Gagliano has been working on the slopes of Pantelleria Island in an effort to find out what can make soil and its biota change enormously over just a few metres. Following her presentation at the EGU General Assembly, she spoke to Sara Mynott, shedding light on what makes volcanic soils so special…

Antonina Lisa Gagliano out in the field. Credit: Antonina Lisa Gagliano

Antonina Lisa Gagliano out in the field. Credit: Antonina Lisa Gagliano

What’s your scientific background, and what drew you to soil biota?

I am a geologist with a background in Natural Sciences and, in 2011, I started my research in biogeochemistry during my PhD in Geochemistry and Volcanology at the University of Palermo. I’ve always tried to look at the interactions between different factors in all sorts of subjects, but if you apply this concept to biotic and abiotic factors, it is particularly interesting and fascinating. I started the study on soil biota when my supervisors introduced me to the biogeochemistry of a geothermal area, thinking that I could have enough scientific background and enthusiasm to start studying something new in our team.

Tell me about your field site – what makes it a great place to study?

Pantelleria Island, a volcano located in the Sicily channel, is a really interesting place. It is an active volcanic system – at present quiescent – that hosts a high-energy geothermal system, with a high temperature gradient and gaseous manifestations all over the island. We studied the most active area, Favara Grande, sampling soils and soil gases from its geothermal field. A first look at the island’s geochemistry suggested high methane fluxes from the soil and high surface temperatures – reaching up 62 °C at only 2 cm below the surface. Indirect evidence of methanotrophic activity led us to better investigate soil biota and how it interacts with methane emissions. It is a great place to study because the peculiar composition of the geofluids is extraordinarily rich in methane and hydrogen, and because the geothermal system is stable both in space and time.

Geothermal area at Favara Grande, Pantelleria Island, Italy. Credit: Walter D’Alessandro.

Geothermal area at Favara Grande, Pantelleria Island, Italy. Credit: Walter D’Alessandro.

During the General Assembly, you highlighted key differences in soil sites that were only 10 metres apart – what did you find and why are they different?

We investigated two really close sites in the Favara Grande geothermal field. They released similar gases (CH4, H2, CO2) and had similar surface temperatures, but at the same time they showed differences in soil chemistry (in particular, pH, NH4+, H2O, sulphur, salinity, and oxides). Amazingly, one site showed high methane consumption and the other was totally inactive, despite both sites being characterised by high methane emissions.

These differences were due to the hydrothermal flux from the ground. As the gasses rise, the gas mixture is influenced by several factors including changes in soil and subsoil properties, such as fracturing, level of alteration, permeability and many others. Variations in even only one of these factors can change the flux velocity, which directly regulates soil temperature. When the temperature goes below 100 ⁰C the most soluble species (H2S and NH3), start to dissolve, releasing hydrogen ions and changing the soil’s characteristics.

The condition of one site was much more mild than the other (higher pH, lower amounts of NH4+, sulphur, soil water content and salinity). These differences were due to a lowering of the hydrothermal flux velocity in deeper layers at the milder site, leading to the depletion of soluble species in the surface soil layers. These conditions created two totally different environments for bacterial populations thriving in the two sites.

How did you identify the different species? How many did you find?

Nowadays, Next-Generation-Sequencing techniques (NGS) are available to screen the microbiota in different substrates. We extracted total bacterial and archeal DNA from soil samples and from the geothermal field at Favara Grande. We found an extraordinary diversity of methanotrophs, that use methane as sole source of carbon and energy in the milder site. In the harsher site, we found a high diversity of chemolithotrophs, that use inorganic reduced substrates to produce energy. Here, there was no methanotrophic activity, nor any evidence of the presence of methanotrophs.

On the left, the harsher site – the stains on the surface are signs of the soil alteration. To the right, the milder site – here, soil alteration is much harder to see without a microscope. Credit: Walter D’Alessandro.

On the left, the harsher site – the stains on the surface are signs of the soil alteration. To the right, the milder site – here, soil alteration is much harder to see without a microscope. Credit: Walter D’Alessandro.

Has anything like this been found before, perhaps at another volcanic site, hot spring or hydrothermal vent?

Currently, integrated studies of bacteria thriving in geothermal soils are still at the pioneer stage and few studies on similar work are available; What we found in terms of chemolithotrophic species is similar to other volcanic sites, but the diversity of methanotrophs detected in our soil samples seem to be unique, probably because the geothermal soils are still under-investigated in this regard.

What do you hope to work on next?

Several questions regarding the relationship between biotic and abiotic factors at our sampling sites are open, so our next challenge is to better investigate the dynamics in this geothermal field. We would also like to extend this research to other sites and establish new collaborations to study different areas and discover new things.

What are your biggest challenges in the field and how do you overcome them?

The first challenge is to find a good sampling site; sampling is like a closed box, particularly when you don’t have anything for comparison terms or any state of art equipment at your disposal. But we overcome these challenges with good planning ahead of the field campaign.

If you could give an aspiring biogeochemist one piece of advice, what would it be?

Biogeochemistry puts together several spheres of knowledge (geochemistry and biology, above all), so my first advice is never stop studying, because when you think to know a lot about something, it’s likely that you may completely overlook the other aspects of the argument. Secondly, go outside the scheme of classical and sectorial research and collaborate with scientists of different sectors to increase your expertise and look at problems from other points of view.

Interview by Sara Mynott, PhD student at the University of Exeter.

Imaggeo on Mondays: The largest fresh water lake in world

Lake shore in Siberia. Credit: Jean-Daniel Paris (distributed via imaggeo.egu.eu)

Lake shore in Siberia. Credit: Jean-Daniel Paris (distributed via imaggeo.egu.eu)

Most lakes in the Northern hemisphere are formed through the erosive power of glaciers during the last Ice Age; but not all. Lake Baikal is pretty unique. For starters, it is the deepest fresh water lake in the world. This means it is the largest by volume too, holding a whopping 23,615.39 cubic kilometres of water. Its surface area isn’t quite so impressive, as it ranks as the 7th largest in the world. However, it makes up for that by also being the world’s oldest lake, with its formation dating back 25 million years – a time during which mammals such as horses, deer, elephants, cats and dogs began to dominate life on Earth.

Located in a remote area in Siberia, perhaps, most impressive of all is how Lake Baikal came to be. It is one of the few lakes formed through rifting. The lake is in fact, one of only two continental rifted valleys on our planet. Typically, “continental rift zones are long, narrow tectonic depressions in the Earth’s surface”, writes Hans Thybo, lead author of a paper on the subject. The Baikal rift zone developed in the last 35 million years, as the Amurian and Eurasian Plate pull away from one another. Eventually, the stretching of the Earth’s surface, at continental rifted margins, can lead to continental lithosphere splitting and the formation of new oceanic lithosphere. Alternatively, as is the case in Siberia, extensive sedimentary basins can be formed; bound by faults, they are known as grabens. It is by this process that Lake Baikal was formed and now houses around 20% of the world’s fresh water!

But this is not where the amazing facts about today’s Imaggeo on Monday’s picture end. The lake is the origin of the Angara River, along which you’ll find the manmade Bratsk Dam, the world’s second largest dam! The shoreline pictured in this photo by Jean- Daniel Paris, is from this impressive dam. Completed in 1964, this artificial reservoir is home to almost 170 billion cubic meters of water (equivalent to the volume held by 68 million Olympic sized swimming pools!).

However, it’s not the impressive water bodies in this inaccessible location in Siberia that are of interest to Jean-Daniel. In fact, this photograph was taken from a research aircraft, which flew over the region for an investigation that spanned a period of several years. Its aim was to measure how concentrations of CO2 and CO varied across the region. Acquiring this data would allow the team of scientist to better understand the sources of the gases, in this remote area of Russian, due to anthropogenic activities and biomass burning.

Reference

Thybo, H., Nielsen, C.A.: Magma-compensated crustal thinning in continental rift zones, Nature, 457, 873-876, doi: 10.1038/nature07688, 2009

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Geosciences Column: Fire in ice – the history of boreal forest fires told by Greenland ice cores.

Burning of biomass contributes a significant amount of greenhouses gases to the atmosphere, which in turn influences regional air quality and global climate. Since the advent of humans, there has been a significant increase in the amount of biomass burning, particularly after the industrial revolution. What might not be immediately obvious is that, (naturally occurring) fires also play a part in emitting particulates and greenhouse gases which can absorb solar radiation and contribute to changing Earth’s climate. Producing a reliable record of pre-industrial fire history, as a benchmark to better understand the role of fires in the carbon cycle and climate system, is the focus of research recently published in the open access journal, Climate of the Past.

Forest fires.  Credit: Sandro Makowski (distributed via imaggeo.egu.eu) http://imaggeo.egu.eu/view/916/

Forest fires. Credit: Sandro Makowski (distributed via imaggeo.egu.eu)

Did you know the combustion of biomass can emit up to 50% as much CO2 as the burning of fossil fuels? The incomplete burning of biomass during fires also produces significant amounts of a fine particle known as black carbon (BC). Compare BC to more familiar greenhouse gases such as methane, ozone and nitrous oxide and you’ll find it absorbs more incoming radiation than the usual suspects. In fact, it is the second largest contributor to climate change.

NEEM camp position and representation of boreal vegetation and land cover between 50 and 90 N. Modified from the European Commission Global Land Cover 2000 database and based on the work of cartographer Hugo Alhenius UNEP/GRIP-Arendal (Alhenius, 2003). From Zennaro et al., (2014).

NEEM camp position and representation of boreal vegetation and land cover between 50 and 90 N. Modified from the European Commission Global Land Cover 2000 database and based on the work of cartographer Hugo Alhenius UNEP/GRIP-Arendal (Alhenius, 2003). From Zennaro et al., (2014). Click to enlarge.

The boreal zone contains 30% of the world’s forests, including needle-leaved and scale-leaved evergreen trees, such as conifers. They are common in North America, Europe and Siberia, but fires styles in these regions are diverse owing to differences in weather and local tree types. For instance, fires in Russia are known to be more intense than those in North America, despite which they burn less fuel and so produce fewer emissions. All boreal forest fires are important sources of pollutants in the Arctic. Models suggest that in the summertime, the fires in Siberian forests are the main source of BC in the Artic and shockingly, exceed all contributions from man-made sources!

To build a history of forest fires over a 2000 year period the researchers used ice cores from the Greenland ice sheet. Compounds, such as ammonium, nitrate, BC and charcoal (amongst others), are the product of biomass burning, and can be measured in ice cores acting as indicators of a distant forest fires. Measure a single compound and your results can’t guarantee the signature is that of a forest fire, as these compounds can often be released during the burning of other natural sources and fossil fuels. To overcome this, a combined approach is best. In this new study, researchers measured the concentrations of levoglucosan, charcoal and ammonium to detect the signature of forest fires in the ice. Levoglucosan is a particularly good indicator because it is released during the burning of cellulose – a building block of trees – and is efficiently injected into the atmosphere via smoke plumes and deposited on the surface of glaciers.

The findings indicate that spikes in levoglucosan concentrations measured in the ice from the Greenland ice sheet correlate with known fire activity in the Northern Hemisphere, as well as peaks in charcoal concentrations. Indeed, a proportion of the peaks indicate very large fire events in the last 2000 years. The links don’t end there! Spikes in concentrations of all three measured compounds record a strong fire in 1973 AD. Taking into account errors in the age model, this event can be correlated with a heat wave and severe drought during 1972 CE in Russia which was reported in The New York Times and The Palm Beach Post, at the time.

Ice core. Credit: Tour of the drilling facility by Eli Duke, Flickr.

Ice core. Credit: Tour of the drilling facility by Eli Duke, Flickr.

The results show that a strong link exists between temperature, precipitation and the onset of fires. Increased atmospheric CO2 leads to higher temperatures which results in greater plant productivity, creating more fuel for future fires. In periods of draught the risk of fire is increased. This is confirmed in the ice core studied, as a period of heightened fire activity from 1500-1700 CE coincides with an extensive period of draught in Asia at a time when the monsoons failed. More importantly, the concentrations of levoglucosan measured during this time exceed those of the past 150 years, when land-clearing by burning, for agricultural and other purposes, became common place. And so it seems that the occurrence of boreal forest fires has, until now, been influenced by variability in climate more than by anthropogenic activity. What remains unclear is what the effects of continued climate change might have on the number and intensity of boreal forest fires in the future.

By Laura Roberts Artal, EGU Communications Officer

 

Reference

Zennaro, P., et al.: Fire in ice: two millennia of boreal forest fire history from the Greenland NEEM ice core, Clim. Past, 10, 1905-1924, doi:10.5194/cp-10-1905-2014, 2014.

Imaggeo on Mondays: Fly away, weather balloon

Some aspects of Earth Science are truly interdisciplinary and this week’s Imaggeo on Mondays photograph is testament to that. The maiden voyage of the research cruise SA Agulhas II offered the perfect opportunity to combine oceanographic research, as well as climate science studies. Raissa Philibert, a biogeochemistry PhD student, took this picture of the daily release of a weather balloon by meteorologists from the South African Weather Services.

Fly away, weather balloon! Credit: Raissa Philibert (distributed via imaggeo.egu.eu)

Fly away, weather balloon! Credit: Raissa Philibert (distributed via imaggeo.egu.eu)

The highlights of Raissa trip aboard the ship include

“the multidisciplinary aspects of the cruise. It was fascinating talking to people doing such different things. Being on the first scientific cruise aboard the vessel was also extremely exciting as well as going to the southern ocean in winter as this provides such rare datasets.”

This cruise was an excellent opportunity for scientists ranging from physical oceanographers, biogeochemists, meteorologists, ornithologists and zoologists to collect data. The two main scientific programmes aboard the cruise aimed to understand 1) the seasonal changes in the carbon cycle of the Southern Ocean, and 2) gain a better understanding of the modifications in water composition caused by the meeting and mixing of the Indian and Atlantic Oceans in the Agulhas Cape region in South Africa.

Understanding both of these processes is important because they impact on the global thermohaline circulation (THC), which is strongly related to global climate change. Think of the THC as a giant conveyor belt of water within the Earth’s oceans: warm surface currents, rush from equatorial regions towards the poles, encouraged by the wind. They cool and become denser during the time it takes them to make the journey northwards and eventually sink into the deep oceans at high latitudes. They then find their way towards ocean basins and eventually rise up (upwell if you prefer the more technical terms), predominantly, in the Southern Ocean. En route, these huge water masses transport energy (in the form of heat), as well as solids, dissolved substances and gases and distribute these across the planets Oceans. So you can see why understanding the THC is crucial to researchers wanting to better understand climate change.

This map shows the pattern of thermohaline circulation. This collection of currents is responsible for the large-scale exchange of water masses in the ocean, including providing oxygen to the deep ocean. The entire circulation pattern takes ~2000 years. Credit: Nasa Earth Observatory.

This map shows the pattern of thermohaline circulation. This collection of currents is responsible for the large-scale exchange of water masses in the ocean, including providing oxygen to the deep ocean. The entire circulation pattern takes ~2000 years. Credit: Nasa Earth Observatory.

The THCs also plays a large part in the carbon cycle in the oceans. Microscopic organisms called phytoplankton drive the main biological processes through which the ocean takes up carbon. They photosynthesise like plants which mean that they use carbon dioxide and water along with other nutrients to make their organic matter and grow. After some time, the phytoplankton die and their organic matter sinks. Part of this organic matter and carbon will remain stored in the deep ocean under various forms until it is brought back up thousands of years later by the THC. Through this cycle, phytoplankton play a major role in controlling the amount of carbon dioxide in the atmosphere and hence, also the Earth’s climate.

 

By Laura Roberts, EGU Communications Officer, and Raissa Philibert, PhD Student.

If you pre-register for the 2015 General Assembly (Vienna, 12 – 17 April), you can take part in our annual photo competition! From 1 February up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

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