GeoLog

climate change

Imaggeo on Mondays: A solitary floating island

With 2014 officially named the hottest year on record, there is evidence of the effects of rising global temperatures across the globe. The solitary, shimmering iceberg in today’s Imaggeo on Mondays photograph is a reminder that one of the best places to look for evidence of change is in glaciers. Daniela Domeisen tells the story of this lonely frozen block of ancient ice.

Iceberg on Tasman glacier lake. Credit: Daniela Domeisen (distributed via imaggeo.egu.eu)

Iceberg on Tasman glacier lake. Credit: Daniela Domeisen (distributed via imaggeo.egu.eu)

The picture shows an iceberg on Tasman glacier lake in the Southern Alps of New Zealand, in the centre of Aoraki / Mount Cook National Park. The lake consists of melt water from the Tasman glacier, which calves into the lake at its far end. The glacier is one of the largest in New Zealand and flows along New Zealand’s highest peaks, Mt Tasman and Mt Cook.

As most glaciers on Earth, the glaciers in Aoraki / Mount Cook National Park are retreating at a fast pace. The lower parts of the Tasman glacier are at less than 1000m above sea level and are therefore melting especially fast. The Tasman glacier lake has formed over the past two to three decades and has in the meantime reached a length of several kilometers. It is projected to almost double in size as the glacier retreats further.

Icebergs constantly calve from the Tasman glacier into the lake and drift down the lake, driven by a weak current towards the lake’s outflow while melting in the process. The ice contained in the icebergs is several thousand years old, beautifully transparent and clean when looking at a single piece of it.

The pictured iceberg was about 10 meters wide. From its shape, and melting pattern, it is likely that it had turned to its side after calving into the lake. With some force it was possible to tip the smaller icebergs and see a shiny blue surface which had been beautifully polished by the water.

On the lake, everything was completely peaceful and quiet, except for the distant sound of a continuous rippling and trickling coming from the moraines on the sides of the lake, as pictured in the background of the photo. Stones and rocks of various sizes slid down and fell into the lake as the ice inside the moraines melted in the bright, sunny and warm January weather.

The changes which are observed in most places as a result of the changing climate are often either too slow to be observed or invisible to the naked eye. The glacier, its lake and icebergs, however, are continuously changing, and a couple of hours spent on the water give a lively impression of a quiet place where things are changing fast enough to be able to observe a notable difference between the time one enters and leaves the place. The beauty of the glacier and its lake with the glittering icebergs provide a spectacular glimpse of a transient place.

By Daniela Domeisen, Research Analyst, MarexSpectron, London

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/.

Imaggeo on Mondays: Iceberg at midnight

Standing on the vast expanse of gleaming white sea ice of the Atka Bay, Michael Bock took this stunning picture of an Antarctic iceberg. The days, during the Antarctic summer, are never ending. Despite capturing the image at midnight, Michael was treated to hazy sunlight.

Icebergs at midnight. Credit: Michael Bock (distributed via imaggeo.egu.eu)

Icebergs at midnight. Credit: Michael Bock (distributed via imaggeo.egu.eu)

“Clearly visible [in the iceberg] are the annual snow accumulation layers which illustrate how the ice archive works.; as you look down the icy face, the ice gets older,” explains Michael. As more snow accumulates on the surface of the glacier, the underlying layers of snow are compressed by the weight from above, hence layers become thinner with increasing depth. On the ice shelf or on the Antarctic plateau these accumulation layers can only be seen when digging a snow pit. The obvious limitation of this is that only a few meters can be excavated with spades, limiting the observations one can carry out. Instead, to gain information about what happens deep within the ice pack, drill cores are usually used. Long cores of the layers of ice can be extracted , providing useful data. “One can drill into the ice (typically on the Antarctic plateau on ice divides or domes) reaching down to bedrock, with the retrieved ice core revealing long records of climatic history,” adds Michael. Deep ice cores can be more than 3000 m long. Depending on e.g. annual mean temperature and accumulation rate the age and resolution of these archives can vary greatly. Whilst this iceberg cannot be studied directly due to hazards associated with working underneath it does “serve as a beautiful visualisation of what we are searching for in ice core science”, explains Michael.

By Laura Roberts Artal and Michael Bock.

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/.

Imaggeo on Mondays: A single beam in the dancing night lights

Laser and auroras. (Credit: Matias Takala distributed via imaggeo.egu.eu)

Laser and auroras. (Credit: Matias Takala distributed via imaggeo.egu.eu)

Research takes Earth scientists to the four corners of globe. So, if you happen to have a keen interest in photography and find yourself doing research at high latitudes, chances are you’ll get lucky and photograph the dancing night lights: aurora (or northern lights), arguably one of the planet’s most breath taking natural phenomenon. That is exactly the position Matias Takala, a researcher at the Finnish Meteorological Institute (FMI), was in when he was able to take this incredible photograph of the swirling aurora and a single beam of green penetrating the Finnish night sky.

The green beam is emitted by Lidar (the Mobile Aerosol Raman Lidar, MARL, to be more precise). This lidar system is designed to measure tropospheric and stratospheric aerosol profiles (backscatter, size distribution, mass), tropospheric water vapour and clouds, with the ability to distinguish between particulates such as dust, ash, and smoke from biomass burning. The system is based at the Arctic Research Centre (ARC) at Sodankylä. Because environmental change is most pronounced in the Polar Regions, the location is ideal to study the effects of a warming climate as a result of environmental changes brought about by the activities of humans.

The high latitude position of the research station means it is also ideally located to contribute to the continuous monitoring of ionospheric activity. Think of the ionosphere as a ring, 85 km to 600 km above the Earth’s surface, of electrons, electrically charged atoms and molecules that surround the Planet. It is here that aurora are generated as incoming charged particles from solar wind collide with the electrons and atoms of gas in the ionosphere. A network of FMI auroral cameras and magnetometers continually survey the sky to provide space weather services, including alerts for when the best auroral displays are likely.

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/.

Meltwater ponds halt new sea ice growth

Each September, battered by the relentless sun-filled days of summer, the smooth expanse of the Arctic Ocean reaches the climax of its annual transformation. Replacing the endless blanket of winter ice, a vast jigsaw puzzle stretches across the pole, a mosaic of soggy snow islands floating amid turquoise ponds of meltwater and inlets of dark blue sea. These meltwater ponds have been shown to dramatically accelerate melt rates during the boreal summer, contributing to the decline in Arctic sea ice extent. Now, new research suggests that the influence of meltwater ponds doesn’t end when the mercury begins to drop: ponds may delay the regrowth of sea ice by up to two months, further reducing Arctic sea ice volume by up to 20 percent.

Meltwater ponds grow as existing sea ice melts and the meltwater pools on its surface, covering up to 80 percent of young sea ice and up to 40 percent of older ice. Once formed, the meltwater allows the ice to absorb more solar radiation by lowering its albedo (the amount of sunlight it reflects), and also acts as a reservoir of latent heat. As a result, “the more ponds you have, the more melting you will have,” says Daniela Flocco, a postdoc at the Centre for Polar Observations and Modeling at the University of Reading in the UK and the lead author of the new work, presented this week at the General Assembly of the European Geosciences Union.

Meltwater ponds. (Credit: Don Perovich)

Meltwater ponds. (Credit: Don Perovich)

In her new study, however, she focuses on what happens next: “In September, the ponds are at their maximum extent. Now you have to do something with all that water.” Some of it will be flushed away, leaked through cracks in the ice, or otherwise lost, but some ponds will persist and these ponds must freeze before new sea ice begins to grow. That’s because the way the ice forms depends on the difference in the temperature between the air and the ocean. The ponds lie in between and their warmth changes the equation.

Winter regrowth takes place at the bottom of existing ice as frigid Arctic air temperatures permeate down through the ice, coaxing the water temperature at the ice interface below the freezing point. But the presence of meltwater ponds reverses this gradient; instead of cold temperatures at the top of the sea ice, the meltwater remains at the freezing point, preventing the seawater below from cooling. “That actually stops the freezing at the bottom of the sea ice in the places where you have a pond,” Flocco says. Flocco and her collaborators are developing a relatively simple thermodynamic model to represent and explore the effect of this previously unrecognised process on sea ice dynamics using complex global climate models (GCM).

The results of her preliminary work, conducted in collaboration with Daniel Feltham and others, suggest that meltwater ponds impede regrowth of sea ice until nearly all of the meltwater has refrozen, a process that can take months owing to the depths of some ponds (which can exceed one metre) and to their salinity. Ponds start out slightly salty because they form from sea ice, which contains inclusions of seawater. During refreezing, a lid of ice forms over the pond and grows thicker, excluding salt from the new ice and concentrating it in the water that remains. Because saltier water freezes at a lower temperature, somewhat paradoxically, the more a pond has refrozen, the harder it gets to refreeze the rest.

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On average, Flocco says, meltwater ponds can delay regrowth of sea ice by approximately one and a half months, a significant fraction of the regrowth season. When she implemented her new calculations into the Los Alamos Sea Ice Model (abbreviated CICE), she found that the model predicted a 20 percent reduction in Arctic sea ice volume over an area of 5.5 million square kilometres during the growth period between late August and mid-October if pond dynamics were considered compared to when they were omitted (which has been the norm until now).

However, validating the model estimates will require new observational studies, says Don Perovich, a sea ice researcher at the United States Army’s Cold Regions Research and Engineering Laboratory, who has conducted numerous field campaigns in the Arctic and was not involved in the new work. “I’ve seen the initial phase of pond freeze-up at the end of summer,” Perovich says, confirming the presence and growth of the ice lids Flocco simulates in her model. Due to the harsh conditions in of the Arctic winter, however, he has never observed what happens next. “Experimentally, it would be interesting to follow a variety of ponds through winter.”

It would also be important because meltwater ponds constitute a major uncertainty in sea ice modeling, Perovich says. Flocco thinks delayed refreezing due to meltwater ponds might have cascading effects. Not only do ponds form more readily on more vulnerable, younger ice, but “the more you delay refreezing, the more you get thinner ice,” she says, “and you never know how long it will take for the ice to start growing again properly.”

By Julia Rosen, PhD, Freelance Science Writer

Reference:

Flocco et al., 2014: The impact of refreezing of melt ponds on Arctic sea ice thinning. Geophysical Research Abstracts, Vol. 16, EGU2014-4125