GeoLog

Biogeosciences

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/.

GeoCinema Online: What a difference technology can make.

Advances in technology mean research that was unthinkable some years ago is now possible. For instance, geographically remote areas which were once out of reach have become more accessible through better (not always easier) transportation, so what we understand by ‘remote areas’ has changed significantly over time. The films in this edition of GeoCinema online are fascinating because they showcase how progress in science know-how mean the advancement of our understanding of planet Earth.

A planetary perspective with Landsat and Google Earth engine

Since July 1972, NASA’s Landsat satellites have gathered images over the entire land surface of the Earth. These images, archived at USGS, reveal dynamic changes over time due to human activity (deforestation, urbanization) and natural processes (volcanic eruptions, wildfire). Now, Google Earth Engine allows scientists, researchers and the public to easily view and analyse this treasure trove of planetary data.

Down to the volcano

A team of scientists have set themselves the goal of building an advanced deep ocean laboratory – on the edge of an active submarine volcano, over a mile below the surface. This research certainly pushes the boundaries of what are considered remote areas!

Project Azolla

How a freshwater fern can provide food, feed & biofuel. This video presents the potential of aquatic farming with a special plant: the fresh-water fern Azolla. The new technology showcased in this video highlights how Azolla provides an innovative way of sustainable, renewable farming.

 

Have you experienced the trials and tribulations of field work? You aren’t alone! As showcased in our last GeoCinema post. If you missed any of the series so far why not catch up here?

Stay tuned to the blog for more films!

Credits

A planetary perspective with Landsat and Google Earth engine: Denise Zmekhol, http://www.zdfilms.com/A-PLANETARY-PERSPECTIVE

Down to the Volcano: Nancy Penrose and Anne Boucher, https://www.youtube.com/watch?v=PIUKej4_XMU

Project Azolla, from floating fern to renewable resource: Dan Brinkhuis, https://www.youtube.com/watch?v=O34gTsxyDq8&feature=share&list=UU_-wRQieb9Tr5GFfJS8c84A

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