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Imaggeo on Mondays: Polygon ponds at sunset.

27 Oct

Thinking of the Arctic conjures up images of vast expanses of white icy landscapes punctuated by towering icebergs and a few dark rocky masses; certainly not a green landscape with a series of water pools amongst rolling hills. The image below is perhaps more reminiscent of the temperate Scottish or Welsh countryside; but don’t be fooled, out Imaggeo on Monday’s image was captured by Reinhard Pienitz  (Laval University, Canada) in western Bylot Island, part of the Canadian Arctic Archipelago.

Polygon ponds at sunset. (Credit: Reinhard Pienitz, via imaggeo.egu.eu)

Polygon ponds at sunset. (Credit: Reinhard Pienitz, via imaggeo.egu.eu)

The uniqueness of Bylot Island is due to the convergence of a number of ecosystems. It lies to the north of Baffin Island and is dominated by high mountain peaks and glaciers. The southern plain of the island is at relatively low-elevations and covered by tundra vegetation. Wetlands are common in the low lying terrain where grasses, brown moss and sedges carpet the landscape. Think of them as ‘polar oasis’ which support hundreds of plant species and tens of animal and bird species. In contrast, the slopes of the hills are much drier and support shrubs, grasses and forbs.

The ground in the low-lying areas is perpetually frozen which means the drainage of water from the melted snow is hampered; it is the presence of this permafrost which allows the formation of the widespread wetlands. Year on year, organic matter accumulates, rising upwards, as the permanently wet and cold conditions mean it is very difficult for organic material to break down. As time passes, cyclic layers of peat and permafrost build up. The importance of the wetland ecosystem in the Arctic cannot be underestimated. The peat-rich soils constitute a net sink for carbon during the Holocene and are thought to store 97% of the tundra carbon reserve (Ellis et al., 2008).

Freezing over the winter months and thawing over the (slightly) warmer spring months drives the formation of the polygonal pattern seen across the wetlands of Bylot Island (and many other Arctic regions). As the ground freezes it contracts resulting in the formation of vertical cracks which penetrate the layers of peat and permafrost. The moist soils and meltwaters mean that there is plenty of water available to infiltrate the cracks, especially during spring. As the cold winter months approach the water freezes and the cracks expand, forming what are known as ice wedges, commonly connected at the surface, which give rise to the well-ordered polygonal pattern.

 

References

Ellis, C.J., et al. (2008), Paleoecological Evidence for Transitions between Contrasting Landforms in a Polygon-Patterned High Arctic Wetland, Arctic. Antarctic, und Alpine Research., 40, 4,624-637

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.

The known unknowns – the outstanding 49 questions in Earth Sciences (Part IV)

17 Oct

We are coming to the end of the known unknowns series and so far we have explored issues which mainly affect the inner workings of our planet. Today we’ll take a look at the surface expression of the geological processes which shape the Earth. Topography significantly affects our daily life and is formed via an interplay between primarily tectonics and climate, but it also affected by biological, mechanical and chemical processes at the Earth’s surface. We’ve  highlighted how advances in technology mean detailed study of previously inaccessible areas has now become possible, but that doesn’t mean there aren’t still plenty of questions left unanswered!

Earth’s landscape history and present environment

Drainage patterns in Yarlung Tsangpo River, China (Credit: NASA/GSFC/LaRC/JPL, MISR Team)

Drainage patterns in Yarlung Tsangpo River, China (Credit: NASA/GSFC/LaRC/JPL, MISR Team)

  • Can we use the increasing resolution of topographic and sedimentary data to derive past tectonic and climatic conditions? Will we ever know enough about the erosion and transport processes? Was also the stocasticity of meteorological and tectonic events relevant in the resulting landscape? And how much has life contributed to shape the Earth’s surface?
  • Can classical geomorphological concepts such as ‘peneplanation’ or ‘retrogressive erosion’ be understood quantitatively? Old mountain ranges such as the Appalachian or the Urals seem to retain relief for > 10^8 years, while fluvial valleys under the Antarctica are preserved under moving ice of kilometric thickness since the Neogene. What controls the time-scale of topographic decay? (Egholm, Nature, 2013)
  • What are the erosion and transport laws governing the evolution of the Earth’s Surface? (Willenbring et al., Geology, 2013) Rivers transport sediment particles that are at the same time the tools for erosion but also the shield protecting the bedrock. How important is this double role of sediment for the evolution of landscapes? (Sklar & Dietrich, Geology, 2011, tools and cover effect); (Cowie et al., Geology, 2008, a field example).
  • Can we predict sediment production and transport for hazard assessment and scientific purposes? (NAS SP report, 2010)
  • What do preserved 4D patterns of sediment flow tell us from the past of the Earth? Is it possible to quantitatively link past climatic and tectonic records to the present landforms? Is it possible to separate the signals of both processes? (e.g. Armitage et al., Nature Geosc, 2011).

    Smaller-scale patterns at the limit between river channels and hillslopes (Credit: Perron Group, MIT)

    Smaller-scale patterns at the limit
    between river channels and hillslopes (Credit: Perron Group, MIT)

  • Can we differentiate changes in the tectonic and climate regimes as recorded in sediment stratigraphy? Some think both signals are indeed distinguishable(Armitage et al., Nature Geosc, 2011). Others, (Jerolmack &Paola, GRL, 2010), argue that the dynamics intrinsic to the sediment transport system can be ‘noisy’ enough to drown out any signal of an external forcing.
  • Does surface erosion draw hot rock towards the Earth’s surface? Do tectonic folds grow preferentially where rivers cut down through them, causing them to look like up-turned boats with a deep transverse incision? (Simpson, Geology, 2004).
  • How resilient is the ocean to chemical perturbations? What caused the huge salt deposition in the Mediterranean known as the Messinian Salinity Crisis? Was the Mediterranean truly desiccated? What were the effects on climate and biology, and what can we learn from extreme salt giants like this? (e.g. Hsu, 1983; Clauzon et al., Geology, 1996; Krijgsman et al., Nature, 1999; Garcia-Castellanos & Villaseñor, Nature, 2011). Were the normal marine conditions truly reestablished by the largest flood documented on Earth, 5.3 million years ago? (Garcia-Castellanos et al., Nature, 2009).

The next post will be our final post in the series and we will list open questions on how climate has contributed to shape the surface of planet Earth, from its surface to the emergence of life and beyond.

Have you been enjoying the series so far? Let us know what you think in the comments section below, particularly if you think we’ve missed any fundamental questions.

By Laura Roberts Artal, EGU Communications Officer, based on the article previously posted on RetosTerricolas by Daniel Garcia-Castellanos, researcher at ICTJA-CSIC, Barcelona

Imaggeo on Mondays: Paramo Soil

15 Sep

Paramo Soil. (Credit: Martin Mergili,via imaggeo.egu.eu)

Paramo Soil. (Credit: Martin Mergili,via imaggeo.egu.eu)

What lies between 3000m and 4800m above sea level in the mountains of the Andes? A very special place dominated by an exceptional ecosystem: The Páramo. Picture lush grasslands with a unique population of flora and fauna, some of which is found nowhere else on Earth.

Páramos stretch from Ecuador to Venezuela, across the Northern Andes and also occur at high elevation in Costa Rica. The climate here is changeable; dowsing rains can be immediately followed by clear skies and blazing sunshine. Overall, the areas experience low average temperatures and rates of evaporation but moderate amounts of precipitation. It is this changeable climate that means the Páramo is thought to be an evolutionary hot spot, where biodiversity is budding faster than at any other place on Earth.

However, were it not for the traditional Andean clothing the girl is wearing in our Imaggeo on Monday’s image, you wouldn’t immediately know this photograph was taken close to the equator. Martin Mergili visited the Páramos of Ecuador, back in 2007, as a PhD student of the University of Innsbruck (Austria) on a field trip around the South American country. Martin gives a detailed account of how the Páramo soil pictured in the image came to be:

‘Whilst 100 km to the east, in the lowlands of the Amazon rainforest, organic matter is rapidly decomposed and soils may be tens of metres deep due to extensive weathering, the reverse is the case here, 3000 m higher up. In the tropical highlands of the Páramo, the year round moist and cool regime slows decomposition and weathering. The obvious result is a rather peaty soil, rich in organic content, supporting pasture grounds used for herding sheep.’

The Páramos support the local human population by providing the main source of water in the Andean valleys whilst the grasslands provide extensive fodder for grazing cattle or sheep. To provide fresh appetising grasses farmers regularly burn the natural vegetation. To what extent the soil of the Páramos is altered as a result of this practice is not clear, but it might provide an explanation for the presence of the dark grey layer seen in the photograph.’Alternatively’, explains Martin, ‘as the area is influenced by significant volcanic activity, this layer might well be the result of ash falls.’

A further feature of interest is the sequence of undulating layers below the organic soil: still part of the soil, it represents a set of volcanic or sedimentary strata with varying resistance to weathering and erosion, probably influenced by tectonic forces. A metre below the bottom of the image, you would come across unweathered rocks.

Páramo El Ángel in Ecuador with Espeletia plants (Credit: Martin Mergili via http://www.mergili.at/worldimages/)).

Páramo El Ángel in Ecuador with Espeletia plants (Credit: Martin Mergili via http://www.mergili.at/worldimages/)

By Laura Roberts Artal, EGU Communications Officer and Martin Mergili, BOKU University, Vienna

References

Buytaer. W., Sevink. J., De Leeuw. B., Deckers. J.:   Clay mineralogy of the soils in the south Ecuadorian paramo region, Geoderma, 127, 144-129, 2005

Hofstede. R. G.M.: The effects of grazing and burning soil and plant nutrient concentration in Colombian paramo grasslands, Plant and Soil, 173, 1, 111-132, 1995

 

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: A massive slump

1 Sep

One of the regions that has experienced most warming over the second half of the 20th century is the Potter Peninsula on King George Island in Antartica. It is here that Marc Oliva and his collaborators are studying what the effects of the warming conditions on the geomorphological processes prevailing in these environments.

“Permafrost is present almost down to sea level in the South Shetland Islands, in Maritime Antarctica” says Marc, “in some recent deglaciated environments in this archipelago, the presence of permafrost favours very active paraglacial processes”.

Permafrost is defined as the ground that remains frozen for periods longer than two consecutive years and constitutes a key component of the Cryosphere. However, it is not fully understood how it reacts to climate variability. In this sense, there is an on-going effort to improve our knowledge on these topics by carrying out long–term monitoring of permafrost, as well as of geomorphological processes, in order to better understand the response of the terrestrial ecosystems to recent warming trends.

This weeks’ Imaggeo on Mondays picture shows a massive slump and the exposed permafrost in the shoreline of a lake in Potter Peninsula (King George Island, Maritime Antarctica). Following the deglaciation of this ice-free area paraglacial processes are very active transferring unconsolidated sediments down-slope to the lake.

Slump-permafrost, Potter Peninsula, Antarctica. (Credit: Marc Oliva via imaggeo.egu.eu)

Slump-permafrost, Potter Peninsula, Antarctica. (Credit: Marc Oliva via imaggeo.egu.eu)

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.

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