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Imaggeo on Mondays: Entering a frozen world

21 Jul

Dmitry Vlasov, a PhD Student and junior scientist from Lomonosov Moscow State University, brings us this week’s Imaggeo on Mondays. He shares his experience of taking part in a student scientific society expedition to Lake Baikal.

This picture shows icy shores of Lake Baikal – a UNESCO World Heritage Site and the world’s largest natural freshwater reservoir (containing about one fifth of Earth’s unfrozen surface freshwater). It is also the deepest lake on our planet (1,642 m).

The icy shores of Lake Baikal. (Credit: Dmitry Vlasov, via imaggeo.egu.eu)

The icy shores of Lake Baikal. (Credit: Dmitry Vlasov, via imaggeo.egu.eu)

The aim of the expedition was to do an eco-geochemical assessment of the environment in and around Ulan-Ude (the capital of Republic of Buryatia). Snow samples were collected all around the city to determine their chemical composition and the concentrations of different chemical elements present in the snowpack. We also studied the isotopic composition of snow to help find the sites where air masses form.

Weather-wise, we were lucky – according to locals this winter was a warm and snowy one. The temperature was (only!) -25 to -33 degrees Celsius. Times were tough when strong, cold and piercing winds froze our hands and faces.

To find out the impact of transport and industry on the snow’s chemical composition within the city, we took background snow samples at different distances and in and around it. One such area was set to the northeast of the city, close to the Turka and Goryachinsk settlements across the notch from Ulan-Ude. This photo was taken in that exact spot. It took about 2.5 hours to make the 170 km journey from Ulan-Ude by car, but we didn’t regret it. The scenery was amazing! The cover of ice over the lake sparkled bright blue, despite being exceptionally transparent. Because of the water’s choppy nature, ice on the Lake Baikal often cracks and billows to form a chain of miniature ice mountains, alternated with relatively smooth ice plains. I’d never seen anything like this before.

All the participants were very excited about expedition – it showed the students different sides of scientific life: work in rather hard weather conditions, analytical lab studies, route planning and of course the breathtaking beauty and outstanding power of nature.

By Dmitry Vlasov, PhD Student and junior scientist, Lomonosov Moscow State University

Acknowledgement:

The expedition was carried out with the financial support of the Russian Geographical Society and the Russian Foundation for Basic Research (project № 13-05-41191 and project RGS “Complex Expedition Selenga-Baikal”).

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

Imaggeo on Mondays: Shaken, not stirred – sediment shows signs of past earthquakes

23 Jun

Nore Praet, a PhD student from Ghent University in Belgium, brings us this week’s Imaggeo on Mondays. She sets the scene for an investigation into past earthquakes and explains how peering through a lake’s icy surface and its murky waters, and into the sediment below can help scientists find out more about the impact of earthquakes in the future…

Early this year, I set off with a group of scientists (including Koen De Rycker, Maarten Van Daele and Philipp Kempf) from the Renard Centre of Marine Geology to conduct fieldwork in South-Central Alaska. The reason for our stay was the search for past megathrust earthquakes (earthquakes produced by the subduction of an oceanic tectonic plate under a continental plate), which had an unusually high magnitude and destructive power.

The most recent Alaskan megathrust earthquake was the Great Alaskan Earthquake in 1964, which represents the second largest earthquake ever instrumentally recorded (9.2 on the moment magnitude scale). In order to have an estimate when such a large earthquake may strike again, we need to study the recurrence pattern of past earthquakes. Since megathrust earthquakes typically have recurrence periods of several centuries, historical archives will not suffice. This is where natural archives, like lake sediments, come in. These records have the advantage of going much further back in time, and they are what brought us to Alaska’s Eklutna Lake.

Zooming in on some individual ice crystal aggregates (few centimeters across) and geometric frost patterns on the frozen surface of Eklutna Lake in Southern Alaska. (Credit: Nore Praet via imaggeo.egu.eu)

Zooming in on individual ice crystal aggregates (few centimeters across) and geometric frost patterns on the frozen surface of Eklutna Lake, Alaska. (Credit: Nore Praet via imaggeo.egu.eu)

Lake sediments can contain very distinct earthquake traces because seismic shaking produces underwater landslides that leave well-defined sediment deposits in the lake basin.

Long sediment cores, extending some 15 metres through these deposits, make it possible to construct a palaeoseismic record. From this we can make an estimate of the recurrence rate of megathrust earthquakes. This will be crucial for understanding seismic hazard in South-Central Alaska and, in particular, in the densely populated city of Anchorage.

This photo, taken in early February, captured the moment where we officially started the fieldwork, after checking the thickness of the ice and its stability.

The constant struggle with the almighty Alaskan cryosphere was the real common theme during the fieldwork. The freezing cold, together with ice formation on the coring equipment, seriously hampered the efficiency of the coring operation. It took some time to accept these conditions and adjust to the demanding laws of this harsh wilderness, but once you are willing to invest the energy into working here, every day nature surprises you with her astonishing beauty.

By Nore Praet, Ghent University

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

Imaggeo on Mondays: Plate it up – a recipe for sea ice errors

16 Jun

Last week, a team of cryospheric scientists published a paper in The Cryosphere that showed how tiny plates of ice can lead to spurious estimates of sea ice thickness. This week, we’re featuring their findings, as well as some spectacular sea ice images in the latest in our Imaggeo on Mondays series…

Viewing the poles from above is a stunning sight – a seemingly endless expanse of brilliant white, ridged blue crests, and delicate grey fringes that stretch like lace over the ocean. Such a vantage point also allows scientists to get to grips with what’s happening to these delegate fringes, seeing how far the sea ice stretches from year to year and how its thickness changes over time.

One of the best ways to measure how thick a large expanse of sea ice is, is to measure its elevation, comparing it to the level of the surrounding water to see just how much is floating on the ocean. This can be done swiftly using satellites, which have the added bonus of keeping a continuous record of change over time. But recent research reveals there may be a problem with this technique.

Spying on sea ice from some 20,000 feet above the surface. (Credit: NASA)

Spying on sea ice from some 20,000 feet above the surface. (Credit: NASA)

Beneath sea ice you find a fine crystalline mush composed of thin ice crystals, or platelets. These platelets bridge the boundary between sea ice and the sea below. Because ice is buoyant, this icy mush (aka the sub-ice platelet layer) pushes the sheet of sea ice upwards, increasing its elevation. Small differences in the proportion of platelets below the ice could make it appear thicker than it really is, leading to inaccurate measures of sea ice thickness.

Looking out over Antarctic sea ice. (Credit: Andrew Chiverton via imaggeo.egu.eu)

Looking out over Antarctic sea ice. (Credit: Andrew Chiverton via imaggeo.egu.eu)

To know just how big a difference these platelets make, first you need to know how much solid ice is present in the mush. Using drill hole data collected in 2011, a team of scientists from New Zealand and Canada estimated that solid platelets made up about 16% of the mush beneath Antarctic sea ice. It may not sound much, but this many platelets could cause ice thickness to be overestimated by almost 20%.

You also need to know just how dense the platelets are. If they have a very low density, they can buoy the ice up more, and if they’re denser, they will have less of an affect on sea ice thickness. The findings mean a fair bit of ground-truthing will be needed to get better estimates of sea ice thickness from satellites in the future.

By Sara Mynott, EGU Communications Officer

Reference:

Price, D., Rack, W., Langhorne, P. J., Haas, C., Leonard, G., and Barnsdale, K.: The sub-ice platelet layer and its influence on freeboard to thickness conversion of Antarctic sea ice, The Cryosphere, 8, 1031-1039, 2014.

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

Meltwater ponds halt new sea ice growth

1 May

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.

JR1

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

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