GeoLog

Greenland

Imaggeo on Mondays: Sunset over the Labrador Sea

Ruby skies and calm waters are the backdrop for this week’s Imaggeo image – one of the ten finalist images in this year’s EGU Photo contest.

 Sunset over the Labrador Sea. Credit: Christof Pearce (distributed via  imaggeo.egu.eu)

Sunset over the Labrador Sea. Credit: Christof Pearce (distributed via imaggeo.egu.eu)

“I took the picture while on a scientific cruise in West Greenland in 2013,” explains Christof Pearce, a postdoctoral researcher at Stockholm University. “We spent most of the time inside the fjord systems around the Greenland capital, Nuuk, but this specific day we were outside on the shelf in the open Labrador Sea. The black dot on the horizon toward the right of the image is a massive iceberg floating in the distance.”

Pearce took part in a research cruise which aimed to obtain high-resolution marine sedimentary records, which would shed light on the geology and past climate of Greenland during the Holocene, the epoch which began 11,700 years ago and continues to the present day.

A total of 12 scientists and students took part in the Danish-Greenlandic-Canadian research cruise in the Godthåbsfjord complex and on the West Greenland shelf. By acquiring cores of the sediments at the bottom of the sea floor, the research team would be able to gather information such as sediment lithology, stable isotopes preserved in fossil foraminifera – sea fairing little creatures – which can yield information about past climates, amongst other data. One of the main research aims was to learn more about the rate at which the Greenland Ice Sheet melted during the Holocene and how this affected local climate conditions and the wider climate system.

“The picture was taken approximately 25 kilometres off the shore of west Greenland coast. In this region the water depth is ca. 500 meters,” describes Pearce. “At this location we deployed a so-called gravity corer and took a 6 meter long sediment core from the ocean floor. Based on radiocarbon measurements – by measuring how much carbon 14 is left in a sample, the age of the sampled units can be known – we now know that these 6 meters correspond to approximately 12000 years of sedimentation, and thus it captures a history of climate and oceanography from the last ice age all the way to present day.”

 

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/.

Imaggeo on Mondays: Just Passing

Imaggeo on Mondays: Just Passing

If lucky enough to visit Ilulissat Icefjord, you’d find yourself in a truly ancient landscape. From the up to 3.9 billion year old Precambrian rocks, to ice dating back to the Quaternary Ice Age (2.6 thousand years old) and archaeological remains which evidence the past settlement of this remote Greenlandic outpost, it’s no surprise this stunning location has been declared a UNESCO world heritage site.

Today’s Imaggeo on Mondays photograph was taken by Camille Clerc, at Sermermiut, an old inuit settlement at the mouth of the Ilulissat Icefjord. Located 1,000 km up the west coast of Greenland, in the Bay of Disko Bugt, 250 km inside the Arctic Circle, the icefjord is the sea mouth of Jakobshavn Glacier – one of the few glaciers on Greenland which reaches the sea. Confined either side by ancient Precambrian rocks, the icefjord forms a narrow, 3-6 km wide tidewater ice-stream, where vast amounts of meltwater and ice from the Greenland ice-sheet reach the sea.

Jakobshavn (also known as Sermeq Kujalleq) is Greenland’s fastest moving glacier. Huge chunks of ice break off the glacier front via Ilulissat Icefjord in a process known as glacier calving. Annually, over 35 km3 of ice is calved into the sea; equivalent to 10% of the production of all Greenland calf ice and more than any other glacier outside Antarctica! As a result, there is an almost constant production of icebergs, which vary in size from small lumps to bergs which can exceed 100m height. As they make their way towards the sea, the icebergs actively erode the fjord bed, slowly changing its morphology over time.

The tragic sinking of the Titanic on its maiden voyage, as a result of a collision with an iceberg on the night of the 15th April 1912, is part of modern history and was even portrayed in a Hollywood blockbuster. Could one of the mighty icebergs calved from Jakobshavn via Ilulissat Icefjord, be the culprit of the sinking of the White Star Line vessel? Pinpointing the exact location from which the glacier was calved is tricky. Most icebergs found in North Atlantic waters originate from the western coast of Greenland. They are pushed slowly towards more northerly latitudes by the West Greenland Current and then forced towards the Atlantic, hugging the coast of Canada, by the Labrador Current, eventually making their way to the Gulf Stream, along one of the world’s busiest shipping routes. The journey there is long and more often than not, the icebergs take such battering during the voyage that their original size is much diminished.

 

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: Recent and future changes in the Greenland Ice Sheet

Geosciences Column: Recent and future changes in the Greenland Ice Sheet

Over the past few decades, the Arctic region has warmed more than any other on Earth. The Greenland Ice Sheet is losing mass faster than ever before, and is expected to keep melting with consequences for global sea-level rise and ocean circulation. At a media briefing, during the EGU’s General Assembly in April (stream it here), researchers presented new results on the factors that influence the Greenland Ice Sheet’s rapid and profound changes – from glacial lakes to clouds and snow darkening.

The vast expanse of the Greenland Ice Sheet covers an area of 1.71 million km2 (approximately a tenth of the size of Russia), and holds a staggering volume of ice: 2.85 million km3. The ice sheet is only rivalled in size by one other: the Antarctic Ice Sheet. Scientist have calculated that the Greenland Ice Sheet stores enough freshwater to raise sea level by 7.4m, should all the ice melt, so understanding what causes the ice to melt now and in the future is critical!

The importance of clouds

When you think of clouds, you probably think of them as purveyors of rain and bad weather. But that is not all; clouds form an intrinsic part of the climate system which is more complex than simply how they affect day to day weather. In Greenland, (as elsewhere across the globe), clouds are a source of precipitation, bringing all-important snow which accumulates on the ice sheet and makes it grow in size.

Southern Tip of Greenland.  Satellite Image by  NASA. Source: Wikimedia Commons

Southern Tip of Greenland. Satellite Image by NASA. Source: Wikimedia Commons

Clouds also affect temperatures: on a clear day you’ll feel the warmth of the sun on your back, but as night falls temperatures start dropping quickly as heat is lost to the atmosphere. However, if in the late afternoon the clouds started rolling in, the night would be warmer, as clouds stop heat being lost to the atmosphere. If they stick around long enough though, they promote cooling, as they reflect sunlight away from the Earth’s surface.

“On a global scale, clouds (on average) tend to cool the Earth’s surface, but there are many regional differences”, explained Kristof Van Tricht,(a PhD student at the University of Leuven in Belgium), during the press conference.

It turns out that, in Greenland, the warming effect of clouds dominates, and warming of the surface encourages melting of the ice sheet. However, the remoteness of the area means that direct observations of just how much the clouds warm the surface and to what extent this impacts on the ice sheet has been limited. Until now.

Using satellite observations, Van Tricht and his team have been able to study the warming effect of clouds in more detail than ever before. Their models show that, in the presence of clouds, the Greenland Ice Sheet can be up to 1.2°C warmer, which can cause substantial melting. Compared to models ran without cloud cover, the ice sheet could melt up to 38% more. This equates to 12% more runoff from the ice sheet into the oceans, solely due to the presence of clouds.

Predictions of what the findings mean for the ice sheet in the future are tricky though. The scientists’ model is based on real-time observations and so it isn’t possible to look into the future. For that, improved cloud model simulations are needed.

Beautiful lakes

Lakes form, seasonally, on the surface of the Greenland Ice Sheet as a result of run-off water pooling in depressions in the ice. Although beautiful to look at, because they are darker than the surrounding ice, they attract more heat. The lakes also drain sporadically, and when they do, some of the water they hold drains through the ice making its way to the base of the ice sheet. Once there, the water lubricates the base of the ice sheet and promotes it to flow more easily and quickly towards the ocean. Combined, these two effects affect the dynamics of the ice sheet.

 Drained Supraglacial Lake Bed. This lake has drained through the bottom for several years in a row. The large block was initially formed in summer of 2006, but large cracks run through it from subsequent lake drainages.  Credit: Ian Joughin (distributed via  imaggeo.egu.eu )

Drained Supraglacial Lake Bed. This lake has drained through the bottom for several years in a row. The large block was initially formed in summer of 2006, but large cracks run through it from subsequent lake drainages.
Credit: Ian Joughin (distributed via imaggeo.egu.eu )

At present, the lakes generally form within the ablation zone – the low-altitude regions towards the edges of the ice sheets where ice is lost through melting, evaporation, calving and other processes – where it is already warmest on the ice sheet.

At the press conference, Andrew Sheperd presented research carried out by Amber Leeson, on how the location on the ice at which the supraglacial (meaning they form on the surface of the ice) lakes form might change with a warming climate and what this means for the Greenland Ice Sheet.

As the climate warms, higher altitude regions on the ice sheet will too. Through building a hydrological model, Leeson found that the lakes spread father inland. According to Leeson’s simulation

“by 2050, the lakes have spread about 50 to 100 km further inland, so more of the ice sheet is potentially exposed to this lubrication effect,” added Shepard.

This is equivalent to an estimated 48–53% increase in the area over which they are distributed across the ice sheet as a whole.

Previous studies of how the ice sheet might respond to a warming climate do not consider the effects of the added melt water volume at the base of the ice sheet as a result of more lakes at the surface. Leeson’s findings mean that these models need to be re-run so that scientists can fully understand the potential implications. This is particularly true in terms of the lubrication effect at the base of the ice and whether the ice will more readily slip towards the oceans, potentially heightening the risk of sea level rise.

 By Laura Roberts, EGU Communications Officer

 

Further reading and information

You can stream the full press conference by following this link: http://client.cntv.at/egu2015/PC9.

Details of the speakers at the press conference are available at: http://media.egu.eu/press-conferences-2015/#greenland

This blog post presents only some of the findings which were discussed during the press conference. Other aspects of this press conference where covered in the media, you can find more on those here and by following this link.

Kristof Van Tricht, Gorodetskaya, I.V., L’Ecuyer, T. et al. Clouds enhance Greenland ice sheet mass loss, Geophysical Research Abstracts Vol. 17, EGU2015-12737-1, 2015 (conference abstract).

Amber A. Leeson, Sheperd, A., Briggs, K. et al. Supraglacial lakes on the Greenland ice sheet advance inland under warming climate, Nature Climate Change, 5, 51–55, doi:10.1038/nclimate2463, 2015.

Amber A. Leeson, Sheperd, A., Briggs, K. et al. Supraglacial lakes advance inland on the Greenland ice sheet under warming climate, Geophysical Research Abstracts, Vol. 17, EGU2015-934-1, 2015 (conference abstract).

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.