MIT researchers report that with the loss of sea ice the Arctic Ocean is becoming more of a carbon sink and that the amount of carbon taken up by the Arctic is increasing by 1 megaton each year.

Click to enlarge. Courtesy: NOAA.

By Jennifer Chu, MIT News

For the past three decades, as the climate has warmed, the massive plates of sea ice in the Arctic Ocean have shrunk: In 2007, scientists observed nearly 50 percent less summer ice than had been seen in 1980.

Dramatic changes in ice cover have, in turn, altered the Arctic ecosystem — particularly in summer months, when ice recedes and sunlight penetrates surface waters, spurring life to grow. Satellite images have captured large blooms of phytoplankton in Arctic regions that were once relatively unproductive. When these organisms die, a small portion of their carbon sinks to the deep ocean, creating a sink, or reservoir, of carbon.

Now researchers at MIT have found that with the loss of sea ice, the Arctic Ocean is becoming more of a carbon sink. The team modeled changes in Arctic sea ice, temperatures, currents, and flow of carbon from 1996 to 2007, and found that the amount of carbon taken up by the Arctic increased by 1 megaton each year.

But the group also observed a somewhat paradoxical effect: A few Arctic regions where waters were warmest were actually less able to store carbon. Instead, these regions — such as the Barents Sea, near Greenland — were a carbon source, emitting carbon dioxide to the atmosphere.

While the Arctic Ocean as a whole remains a carbon sink, MIT principal research scientist Stephanie Dutkiewicz says places like the Barents Sea paint a more complex picture of how the Arctic is changing with global warming.

“People have suggested that the Arctic is having higher productivity, and therefore higher uptake of carbon,” Dutkiewicz says. “What’s nice about this study is, it says that’s not the whole story. We’ve begun to pull apart the actual bits and pieces that are going on.”

A paper by Dutkiewicz and co-authors Mick Follows and Christopher Hill of MIT, Manfredi Manizza of the Scripps Institute of Oceanography, and Dimitris Menemenlis of NASA’s Jet Propulsion Laboratory is published in the journal Global Biogeochemical Cycles.

The ocean’s carbon cycle

The cycling of carbon in the oceans is relatively straightforward: As organisms like phytoplankton grow in surface waters, they absorb sunlight and carbon dioxide from the atmosphere. Through photosynthesis, carbon dioxide builds cell walls and other structures; when organisms die, some portion of the plankton sink as organic carbon to the deep ocean. Over time, bacteria eat away at the detritus, converting it back into carbon dioxide that, when stirred up by ocean currents, can escape into the atmosphere. The MIT group developed a model to trace the flow of carbon in the Arctic, looking at conditions in which carbon was either stored or released from the ocean. To do this, the researchers combined three models: a physical model that integrates temperature and salinity data, along with the direction of currents in a region; a sea ice model that estimates ice growth and shrinkage from year to year; and a biogeochemistry model, which simulates the flow of nutrients and carbon, given the parameters of the other two models. The researchers modeled the changing Arctic between 1996 and 2007 and found that the ocean stored, on average, about 58 megatons of carbon each year — a figure that increased by an average of 1 megaton annually over this time period. These numbers, Dutkiewicz says, are not surprising, as the Arctic has long been known to be a carbon sink. The group’s results confirm a widely held theory: With less sea ice, more organisms grow, eventually creating a bigger carbon sink.

A new counterbalance

However, one finding from the group muddies this seemingly linear relationship. Manizza found a discrepancy between 2005 and 2007, the most severe periods of sea ice shrinkage. While the Arctic lost more ice cover in 2007 than in 2005, less carbon was taken up by the ocean in 2007 — an unexpected finding, in light of the theory that less sea ice leads to more carbon stored. Manizza traced the discrepancy to the Greenland and Barents seas, regions of the Arctic Ocean that take in warmer waters from the Atlantic. (In warmer environments, carbon is less soluble in seawater.) Manizza observed this scenario in the Barents Sea in 2007, when warmer temperatures caused more carbon dioxide to be released than stored. The results point to a subtle balance: An ocean’s carbon flow depends on both water temperature and biological activity. In warmer waters, carbon is more likely to be expelled into the atmosphere; in waters with more biological growth — for example, due to less sea ice — carbon is more likely to be stored in ocean organisms. In short, while the Arctic Ocean as a whole seems to be storing more carbon than in previous years, the increase in the carbon sink may not be as large as scientists had previously thought.“The Arctic is special in that it’s certainly a place where we see changes happening faster than anywhere else,” Dutkiewicz says. “Because of that, there are bigger changes in the sea ice and biology, and therefore possibly to the carbon sink.”Manizza adds that while the remoteness of the Arctic makes it difficult for scientists to obtain accurate measurements, more data from this region “can both inform us about the change
in the polar area and make our models highly reliable
for policymaking decisions.” This research was supported by the National Science Foundation and the National Oceanic and Atmospheric Administration.

Abstract

The rapid recent decline of Arctic Ocean sea ice area increases the flux of solar radiation available for primary production and the area of open water for air-sea gas exchange. We use a regional physical-biogeochemical model of the Arctic Ocean, forced by the National Centers for Environmental Prediction/National Center for Atmospheric Research atmospheric reanalysis, to evaluate the mean present-day CO₂ sink and its temporal evolution. During the 1996–2007 period, the model suggests that the Arctic average sea surface temperature warmed by 0.04°C a⁻¹, that sea ice area decreased by ∼0.1 × 106 km2 a⁻¹, and that the biological drawdown of dissolved inorganic carbon increased. The simulated 1996–2007 time-mean Arctic Ocean CO₂ sink is 58 ± 6 Tg C a⁻¹. The increase in ice-free ocean area and consequent carbon drawdown during this period enhances the CO2 sink by ∼1.4 Tg C a⁻¹, consistent with estimates based on extrapolations of sparse data. A regional analysis suggests that during the 1996–2007 period, the shelf regions of the Laptev, East Siberian, Chukchi, and Beaufort Seas experienced an increase in the efficiency of their biological pump due to decreased sea ice area, especially during the 2004–2007 period, consistent with independently published estimates of primary production. In contrast, the CO₂ sink in the Barents Sea is reduced during the 2004–2007 period due to a dominant control by warming and decreasing solubility. Thus, the effect of decreasing sea ice area and increasing sea surface temperature partially cancel, though the former is dominant.

Citation

“Changes in the Arctic Ocean CO2 sink (1996–2007): A regional model analysis” by M. Manizza, M. J. Follows, S. Dutkiewicz, D. Menemenlis, C. N. Hill R. M. Key published in Global Biogeochemical Cycles

DOI: 10.1002/2012GB004491

Read abstract and get paper here.

Source

This report based on a story from MIT News here.

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Friday, January 10, 2014

The Changing Nature of Power

Delhi’s homeless struggle in near-freezing temperatures as cold spell sweeps India

Updated 54 minutes ago

At least 100 people have been killed in a cold spell sweeping across India, and near freezing temperatures in the capital are making life almost impossible for people living on the streets.

But as Stephanie March discovers, helping the city’s homeless isn’t a straightforward task.

Sitting on a tarpaulin and covered in blankets, 12-year-old Gobind massages his sick mother’s arms as she shivers in the cold.

Since coming from the impoverished north-Indian state of Uttar Pradesh a year-and-a-half ago, he and his family have been sleeping on the footpath outside the AIIMS hospital in South Delhi because of his mother’s medical condition.

“My mother has a respiratory problem,” he said.

“Even in the winter we have to stay here near the hospital.”

While Gobind watches over his mother, his aunt begins making her bed for the night.

She unfolds several cardboard boxes and lays down on top of them, pulling up two thin blankets to cover her.

Around her people have pulled their blankets up over their faces and heads.

The pavement is littered with brightly-coloured, mummified bodies.

Most of them have come from interstate for medical treatment, but are unable to afford accommodation in the city.

While it’s impossible to know how many people are living on the street in the Indian capital, charity groups say the number is probably around 100,000.

Charity groups say about 100 people have died of exposure in India’s north in the last week.

Bus shelters

In a desperate move to protect the city’s homeless people from the bitterly cold winter the Delhi Government has started using abandoned buses as temporary shelters.

The first of 200 buses to be deployed across the city have been placed outside the AIIMS hospital, 50 metres from Gobind and his family.

He says he tried to get his family on one of buses earlier in the night.

“There is no place to stay there today, they are all filled up,” he said.

Over at the bus an elderly man with a patch over one eye looks longingly through the back passenger door, he moves to walk up the stairs, but the social workers catch him.

“Sorry uncle, it is full,” they tell him.

Ram Shri is one of the lucky ones and has been allocated a spot on the bus.

Until tonight she and her ill brother had been sleeping on the pavement.

“At least in here we are safe from the morning dew,” he said.

“In here, my brother is more relaxed.”

Aid groups have praised the initiative, urging the government to move quickly to mobilise the other available buses.

“It is a very good idea because it is a medium we can provide them a home, a shelter where they can survive in such chilly winds,” said Anam Qayium, a social worker with the NGO, Prerna.

‘Professional beggars’

Helping the homeless in Delhi isn’t always straightforward.

With the buses full, armed with a pile of blankets Anam Qayium and her team head to a nearby traffic island beneath an underpass where a dozen people are sleeping.

They try to convince them to come to stay in their permanent shelter; most refuse, but they happily take the blankets.

Away from the group Anam spots another lump covered in cloth and expects to find a person sleeping underneath, but instead she discovers something else – a pile of brand new, neatly folded blankets – probably given to the beggars by other charities or the government.

Anam says they will probably go and sell them at the market – that they are ‘professional beggars’.

“It is just a medium for them to earn money and they are just misusing what we are giving to them,” she said.

“They are not appreciating it – they are not, you know, thankful to us for what we are doing but they are just taking and taking.”

It’s hard to know in Delhi who is truly needy and who is not, but in this extremely cold weather social workers like Anam are leaving nothing to chance.

She and her team head off with their pile of blankets to find the next group of homeless.

Cold soil in the groove

26 Dec

Soil polygons in the Tundra. Photo by Sebastian Zubrzycki. Click to see the original image at Imaggeo.

Often, soils from cold regions, such as Arctic soils, show polygonal forms in their surface. These polygons are formed because of the freeze-thaw cycle, characteristic of permafrost.

What is permafrost?

Permafrost is a subsurface soil layer which stays permanently frozen (below 0 ^oC) during long periods of time, usually more than two consecutive years.

Circum-Arctic Map of Permafrost and Ground Ice Conditions. Credit: J. Brown, O.J. Ferrians Jr., J.A. Heginbottom and E.S. Melnikov. Click to see the original image at Wikimedia Commons.

Most extensive permafrost areas can be found in circumpolar areas from North America (Canada and Alaska), Asia (Siberia), Europe (Norwich), cold continental areas (Tibet) and some islands (South Georgia and the Sandwich Islands, in the Atlantic Ocean). And on Mars!

Phoenix landing-day image near north pole of Mars showing flat terrain, containing what appears to be a polygonal pattern, stretching from the foreground to the horizon. Credit: NASA/Jet Propulsion Lab/University of Arizona. Click to see the original image at Wikimedia Commons.

The soil layer above the permafrost (known as the active layer) is the part of soil that thaws during the warm season and freezes again at the beginning of the cold season, because the influence of air temperature is greater in the first centimeters of soil. Commonly, the thickness of the active layer may vary between 10 and 100 cm depending on the season, aspect, vegetation, soil texture and proximity to water bodies.

Permafrost landscape. Photo by Reinhard Pienitz. Click to see the original image at Imaggeo.

How do polygons form?

Cryoturbation is one of the main processes in the soil active layer. As a consequence, the soil surface in these cold areas often show polygons, circles, steps and stripes formed by stones and fine sediments.

Stone rings on Spitsbergen. Photo by Hannes Grobe. Click to see the original image at Wikimedia Commons.

Repeated groundwater freezing/thawing cycles causes contraction/expansion of soil material, that forces the displacement of coarse gravels and stones over the soil surface. Areas with fine sediments (with low porosity) show larger water contents than those areas where coarse fragments accumulate.

Polygon ponds in Arctic tundra soils. Photo by Reinhard Pienitz. Click to see the original image at Imaggeo.

As a result, water-saturated, finely-textured soil expands and contracts more easily during freezing/thawing cycles than coarsely textured stony areas. In the long term, stone polygons and other patterns may appear on the soil surface. Fine sediments in the center of polygons usually form ponds and small bogs.

Thawing permafrost in Siberia. Photo by Guido Grosse. Click to see the original image at Imaggeo.

Know more

Christensen, P.R. 2006. Water at the poles and in permafrost regions of Mars. Elements 2, 151-155. DOI: 10.2113/gselements.2.3.151.

Dobinski, W. 2011. Permafrost. Earth-Science Reviews 108, 158-169. DOI: 10.1016/j.earscirev.2011.06.007.

Gruber, S. 2012. Derivation and analysis of a high-resolution estimate of global permafrost zonation. The Cryosphere 6, 221-233. DOI: 10.5194/tc-6-221-2012.

Guglielmin, M. 2012. Advances in permafrost and periglacial research in Antarctica: A review. Geomorphology 155-156, 1-6. DOI: 10.1016/j.geomorph.2011.12.008.

Haeberli, W. 2013. Mountain permafrost – research frontiers and a special long-term challenge. Cold Regions Science and Technology 96, 71-76. DOI: 10.1016/j.coldregions.2013.02.004.

Haeberli, W., Noetzli, J., Arenson, L.b Delaloye, R., Gärtner-Roer, I., Gruber, S., Isaksen, K., Kneisel, C., Krautblatter, M., Phillips, M. 2011. Mountain permafrost: Development and challenges of a young research field. Journal of Glaciology 56, 1043-1058. DOI: 10.3189/002214311796406121.

Langer, M., Westermann, S., Muster, S., Piel, K., Boike, J. 2011. The surface energy balance of a polygonal tundra site in northern Siberia – Part 1: Spring to fall. The Cryosphere 5, 67, 79. DOI: 10.5194/tc-5-151-2011.

Langer, M., Westermann, S., Muster, S., Piel, K., Boike, J. 2011. The surface energy balance of a polygonal tundra site in northern Siberia – Part 2: Winter. The Cryosphere 5, 509-524. DOI: 10.5194/tc-5-509-2011.

Lin, Z.H., Zhang, Y.H. 2013. The general review of permafrost temperature research methods. Applied Mechanics and Materials 405-408, 158-161. DOI: 10.4028/www.scientific.net/AMM.405-408.158.

McClymont, A.F., Hayashi, M., Bentley, L.R., Christensen, B.S. 2013. Geophysical imaging and thermal modeling of subsurface morphology and thaw evolution of discontinuous permafrost. Journal of Geophysical Research F: Earth Surface 118, 1826-1837. DOI: 10.1002/jgrf.20114.

Wade F.A., De Wys, J.N. 1968. Permafrost features on the martian surface. Icarus 9, 175-185. DOI: 10.1016/0019-1035(68)90011-0.

Xie, s., Qu, J., Zu, R., Zhang, K., Han, Q., Niu, Q. 2013. Effect of sandy sediments produced by the mechanical control of sand deposition on the thermal regime of underlying permafrost along the Qinghai-Tibet railway: Land Degradation and Development 25, 453-462. DOI: 10.1002/ldr.1141.

Zhao, L., Jin, H. , Li, C., Cui, Z., Chang, X., Marchenko, S.S., Vandenberghe, J., Zhang, T., Luo, D., Guo, D., Liu, G., Yi, C. 2013. The extent of permafrost in China during the local Last Glacial Maximum (LLGM). Boreas. In press. DOI: 10.1111/bor.12049.