GeoLog

Atmospheric Sciences

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/.

GeoTalk: Nick Dunstone, an outstanding young scientist

 Nick Dunstone, the winner of a 2014 EGU Division Outstanding Young Scientists Award, who studies the Earth’s climate and atmosphere, including how they are impacted by natural variation and anthropogenic emissions talks to Bárbara Ferreira, the EGU Media and Communications Manager, in this edition of GeoTalk. This interview was first published in our quarterly newsletter, GeoQ.

NickFirst, could you introduce yourself and tell us a bit about what you are working on at the moment?

My name is Dr Nick Dunstone and I am a climate scientist working at the Met Office Hadley Centre in the UK. Here I work within the Monthly to Decadal Climate Prediction group which focuses on developing regional climate prediction capability for all areas of the globe. The monthly to decadal timescale (often referred to as ‘near-term’ prediction) is an emerging and challenging field of climate prediction which attempts to span the void between shorter term weather forecasts (days to weeks) and longer term climate projections (many decades to centuries) using numerical climate models. So, similar to a weather forecast, near-term climate predictions are initialised close to the observed state of the climate and yet, similar to a climate projection; they also include the projected changes in external forcings such as greenhouse gases, anthropogenic aerosols and the solar cycle. Much of my research over the last few years has concerned the amount of predictability in the climate system arising from slowly varying internal processes (for example, slowly varying ocean dynamics) versus how much is driven by external forcings (e.g. anthropogenic emissions).

Earlier this year, you received a Division Outstanding Young Scientists Award for your work on the coupled ocean-atmosphere climate system and its predictability. Could you tell us a bit more about the research you have developed in this area?

Some of my work has considered the role of internal ocean dynamics in driving predictability in the atmosphere. Often we think of the tropical regions as being the engine of the climate system, driving some of the variability in the mid-latitude atmosphere. However, this is not always the case and especially on longer timescales (multi-annual to decadal), the mid-latitudes can drive tropical variability. My colleagues and I illustrated this using a set of idealised climate model experiments that tested the impact of initialising the state of different parts of the world’s oceans. The results showed that it was key to initialise the ocean’s sub-surface temperature and salinity (and so density) in the high latitude North Atlantic to have skill in predicting the multi-annual frequency of model tropical Atlantic hurricanes. This is intimately linked to correctly initialising the model’s Atlantic meridional overturning circulation, and to the question of what sub-surface ocean observations would be needed to do this. I have also worked on how external forcings, such as anthropogenic emissions from industrial pollution, may impact regional climate variability.

A lot of the work you have developed focuses on the anthropogenic impact on the Earth’s atmosphere and climate. What does your research tell us about the extent of the impact of human activities on the Earth’s natural systems?

In the last couple of years we have examined the possible impact of anthropogenic aerosol emissions on multi-decadal changes in climate variability. We found that when the latest generation of climate models include the historical inventory of anthropogenic aerosol emissions, they are capable of better reproducing the phases of observed multi-decadal variability in North Atlantic temperatures. In our Met Office Hadley Centre climate model, we find that this is principally due to the inclusion of aerosol-cloud interactions. When aerosols are present in clouds they can modify the cloud droplet size (known as the 1st aerosol indirect effect), increasing the reflectivity of the clouds and hence decreasing the amount of solar radiation reaching the ocean surface. Variations in aerosol emissions from North America and Europe due to socioeconomic changes (e.g. rapid post-war industrialisation in the 1950s and 1960s and then the introduction of clean-air legislation in the 1970s and 1980s) then drive fluctuations in North Atlantic temperatures in our climate model. Furthermore, we also showed that the frequency of model North Atlantic hurricanes is also driven primarily by anthropogenic aerosol changes and that it is in phase with the observed changes in Atlantic hurricane frequency. Further work needs to be done to understand if this aerosol mechanism is truly operating in the real world. If so, then our work suggests a significant role for humans in unwittingly modulating regional climate variability (especially in the North Atlantic) throughout the 20th century. This also has profound implications for the next few decades, as North America and Europe continue to clean-up their industrial aerosol emissions, whilst the impact of short-term increases in aerosol emissions from developing economies (e.g. China and India) also needs to be studied. Of course, at the same time, the signal of greenhouse gas warming is likely to become more dominant with associated climate impacts.

What is your view on having the Anthropocene accepted as a formal geological epoch? Do you think there are scientific grounds to define the Anthropocene in such a way, or at least in what your research area is concerned?

This is an interesting question but not one that I’ve thought very much about! From a climate scientist perspective, I think it is fairly obvious that we have entered a time when the human fingerprint extends to all (or at least very nearly all) environments on Earth. We see the fingerprint in the concentration of greenhouse gases and water vapour in the atmosphere, land and sea-surface temperatures, deep-ocean warming, ocean sea-level rise, ocean acidification, etc… If physical climate changes alone were the main criterion, then surely there would be no doubt that we have entered a new epoch. Beyond this though, the wider Earth biological system is also being impacted by human activity. For example, previous epochs have also been defined based upon mass species extinction, so there may also be a case here for viewing the Anthropocene as a time when the actions of humanity have led to species extinction. Of course there are then questions about how to define the beginning of this new epoch. Many suggest a geophysical marker such as the 1940s and 1950s when radionuclides from nuclear detonations first became present. Or would it be when the atmospheric CO2 concentration started to rise above pre-industrial levels in the early nineteenth century? Or would it be earlier still, when we started significantly altering the land-surface via large-scale deforestation? Then when would the Anthropocene end? Could we envisage a time in the future when we effectively remove our influence on the climate system, e.g. returning the atmospheric constituents to pre-industrial ratios? Or, rather more grimly, would the Anthropocene only truly be over when our species itself becomes extinct? Whilst these are very interesting ‘dinner-table’ type discussions, from a working climate scientist viewpoint the definition seems largely academic and we’d probably be better off investing our time into researching how we are changing the planet and predicting the associated climate impacts!

On a different topic, according to your page on the Met Office website, you started your career in science as an astrophysicist. Could you tell us a bit about how you made the transition from astrophysics to climate science, highlighting any difficulties you may have had with making such a career change and how you overcame them? What advice would you have for young scientists looking to make a similar move?

To a large extent I think ‘science is science’! Many of the skills are very transferable, especially between physical, computationally based, subjects, where numerical modelling skills are essential. I’ve now met a surprising number of climate scientists who are ex-astronomers, or from some other branch of physics. I think what you need most of all is the drive for learning new things, and making new discoveries, about the physical world in which we live. I found that this is very transferable, applying equally to astrophysics and climate science. I think you settle into a subject slowly and even though I’ve been working in climate science for over 6 years now, I still have lots to learn about our existing understanding of climate system, and that’s exciting. The important thing to realise however, is that you can still make important and useful contributions to a new field quite quickly, especially one as broad as climate science, given the right guidance or supervision.

Finally, could you tell us a bit about your future research plans?

We need to progress both our understanding of natural (internal) variability in climate models and improve the fidelity of important climate teleconnections (processes linking variability in one part of the climate system with climate impacts in a remote region). At the same time we need to progress our understanding of the relative roles of external vs internal forcing in driving variability and extremes in the climate system. On the shorter (seasonal) timescales I am interested in what drives the year-to-year variability in the winter North Atlantic Oscillation, which our latest Met Office seasonal climate prediction systems can now predict with surprisingly good skill. Much of this work I hope to develop during my new post as manager of the Global Climate Dynamics group in the Met Office Hadley centre that I will start in December.

 

Interview conducted by Bárbara Ferreira

EGU Media and Communications Manager and GeoQ Chief Editor

 

Follow

Get every new post on this blog delivered to your Inbox.

Join other followers: