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

19 Sep

Here is the second instalment in our series covering the biggest unknowns in the Geosciences.

Last week we explored what it is about the Earth’s origin that still remains unclear and this week we probe the Earth’s deep interior. Unlike in Jules Verne’s Journey to the Centre of the Earth, there are no volcanic tubes we can climb down which will allow us to discover the inner workings of our Planet. Direct understanding can only be gained from rock samples; our inability to collect those at depths in excess of 12 km means direct observations are restricted to the Crust. How do we know what happens far down below? We have to rely heavily on indirect measurements such as seismic wave tomography, together with geodynamic and petrological modelling. But, really, how confident can we be, considering we can’t really ‘see’ into the centre of the Earth, that our hypotheses are correct? Only this week, new research casts doubts over the long established theory that hot spot volcanism is fed by deep rooted mantle plumes. This highlights just how important it is to continue efforts to push our understanding and find new and innovative ways to journey into the centre of the Earth.

The Earth’s Interior

Tectonic plates (Credit: USGS, Department of the Interior/USGS)

Tectonic plates (Credit: USGS, Department of the Interior/USGS)

  1. What are the chemical composition and mechanical properties of rocks in the Earth’s mantle at the extreme pressure and temperature they undergo? As planets age and cool off, their internal and surface processes coevolve, chemically and mechanically, shaping in turn the atmospheric composition. Therefore this question has direct implications for our understanding of the environmental evolution of the Earth. (Kerr, 2005, Science)
  2. What are the dynamic processes in the Earth interior that accommodate and fuel plate tectonics? As seismometers spread more evenly over the planet’s surface, the seismic imaging of the interior will rapidly improve, providing a detailed distribution of seismic wave velocity. Simultaneously, lab-based mineral physics must better constrain what these mechanical wave velocities tell us about the hot, deep rocks of uncertain composition in the mantle. Only then will computer models be able to test the currently proposed geodynamic models by trying to quantitatively fit those data with other geophysical observations such as gravity variations. (Kerr, 2005, Science)
  3. How does the Earth’s magnetic field work? Sedimentary and volcanic rocks have recorded changes of the magnetic field throughout the evolution of the Earth. What causes the sudden reversals of the paleomagnetic field? What caused the long periods (more than 10 Myr) with no magnetic inversions (superchrons)? How does the geomagnetic field link to the iron convection properties at the deep Earth? Or inversely, what can we learn about the mechanical behavior of the materials at those depths from the geomagnetic field? (see this nature paper for further context). Are the magnetic reversals too fast to be related to core dynamics? (Biggin et al., 2012, Nature Geoscience). Could their frequency be related to the distribution of tectonic plates? (Pétrélis et al., 2011, GRL). What causes superchrons (periods without reversals)? Something internal within the core, or is it induced externally by the mantle/subducting slabs? Was the geomagnetic field always dipolar, or was it more asymmetric in the past, as suggested in by Biggin et al., (2012)?

    Magnetosphere rendition (Credit: Wikimedia Commons user NASA  http://sec.gsfc.nasa.gov/popscise.jpg)

    Magnetosphere rendition (Credit: Wikimedia Commons user NASA http://sec.gsfc.nasa.gov/popscise.jpg)

  4. What makes the magnetic field change between reversals? What is the history of and what controls the excursions of the rotation pole relative to the surface geography, known as true polar wander? (Creveling et al., 2012, Nature).
  5. How do hotspots come about? Are intraplate hotspots really made by deep sources of uprising materials (mantle plumes) coming from the deepest Earth’s mantle? Or can they be explained by shallower convection? (e.g Morgan, 1971, Nature and Fouch, 2012, Geology)
  6. What are the properties of deep rocks? How can we translate the heterogeneity in density, seismic wave velocity, and electromagnetic resistivity presently observed in the mantle and the lithosphere into variations of the mineralogical composition? And how do these measures relate to the dynamics of the Earth and to key mechanical properties such as the viscosity?  (Faccenna & Becker, 210, Nature)]
  7. What are the causes for and massive flood basalts such as the Columbia River Basalts?

    Distribution of the World’s Large Igneous Provinces (Source: Wikimedia Commons, user: USGS)

    Distribution of the World’s Large Igneous Provinces (Source: Wikimedia Commons, user: USGS)

Do you think these seven questions cover the fundamental issues yet to be addressed when it comes to the Earth’s deep interior? If you’d like to add to this discussion, please feel free to voice your opinions using the comments section below, we really would love to hear from you!

Enjoyed these seven questions? Why not explore the first post in the series?

Coming up next: Plate tectonics and deformation.

 

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

GeoCinema Online: Trials and tribulations of field work.

17 Sep

Field work is not without its trials and tribulations, getting there, for instance can be an adventure in itself. Once you arrive you can expect long days, sandwiches for lunch and frustration at losing your way or equipment not working as you expect it to. Despite all of that, one of the primary draws of the geosciences is being able to spend time in the great outdoors. In the fourth instalment of GeoCinema there is something for everyone as we track scientist living in Antarctica, undergraduates trying to map a 15km2  area in Greenland and a PhD student who spends her time high up in the tree canopy. Grab a drink and get comfortable, the show is about to begin.

Are you ready? Inspirational moments in Antarctica

A short music video contains sequences of science in action which captures a little of how it feels to travel to and work in Antarctica.

British Antarctic Survey Halley Research Station

Living in Antarctica is no mean feat, especially whilst attempting to carry out lengthy field seasons, in fact, to some it might seem utter madness. However, the British Antarctic Survey’s Halley Research Station, a new facility to support world-leading science by offering living quarters as well as research facilities, has been built on the icy landscape.

An Undergraduate Mapping Project
This educational film follows 4 Oxford University undergraduates as they complete their mapping projects and describes the methodology used and experiences gained on the trip. It includes footage from Greenland, photographs and animated diagrams, making geology accessible to people with little knowledge of the subject. The main goal of the film is to inspire secondary school students to undertake fieldwork and study Earth Sciences.

Into the Deep Forest: Remote Sensing and Tropical Leaf Phenology: A PhD in the Amazonian Canopy.

Published research with its detailed graphs, elaborate methodologies and analysis doesn’t provide a means to showcase all the work that goes on behind the scenes. In this film a researcher showcases the first two years of her PhD, spent up high in the canopy of the Amazon rainforest.

 

Have you missed any of the series so far? Catch up with space science here or learn about carbon capture and storage instead.

Stay tuned to the blog for more films!

Credits

Are you ready? Inspirational moments in Antarctica: Linda Capper, http://youtu.be/8CmKwXXPkgg

British Antarctic Survey Halley Research Station: Linda Capper, http://www.youtube.com/watch?v=TDIi7rP_WBA

An Undergraduate Mapping Project: Eleni Wood, http://www.youtube.com/watch?v=Xd5H-14WLzA

Into the Deep Forest: Remote Sensing and Tropical Leaf Phenology: A PhD in the Amazonian Canopy: Cecilia Chavana-Bryant, http://vimeo.com/46676651.

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.

Geosciences Column: Adapting to acidification, scientists add another piece to the puzzle

12 Sep

In the latest Geosciences Column Sara Mynott sheds light on recent research into how ocean acidification is affecting the California Current Large Marine Ecosystem. The findings, published in Biogeosciences, reveal large differences between the abilities of different animals to adapt and highlight the urgent need to understand the way a greater suite of species are responding…

Large Marine Ecosystems (LMEs) are highly productive ocean areas that border the continents. To give you a flavour of just how productive we’re talking, together the world’s LMEs account for 80% of the global marine fisheries catch, making them incredibly important regions both socially and economically. The California Current Large Marine Ecosystem (CCLME) is one such system and covers the length of the US Pacific coast. But, like other ocean ecosystems, the CCLME is under threat from climate change.

Major changes in the carbonate chemistry of the oceans are expected over the next few decades, and changes in the California Current system are to be some of the most rapid. Determining how this system, and indeed other ecosystems, will respond is a significant challenge for biologists, ecologists and climate scientists alike.

In 2010, an interdisciplinary research group known as OMEGAS (Ocean Margin Ecosystems Group for Acidification Studies) set out to find answers by monitoring a ~1300 km stretch of the CCLME that runs from central Oregon to southern California. Because this stretch of ocean can be divided into distinct areas with differing pH and carbonate chemistry, the researchers could compare the characteristics of animals living in more acidic conditions with those living in a less acidic environment and assess their ability to adapt.

Like other LMEs, the California Current system is characterised by upwelling – a process that brings nutrient-rich deep water to the surface. Upwelling waters bring with them a change in pH. In the southern CCLME, there is regular upwelling but in the north it is intermittent. This means animals living off the Oregon coast experience more variable pH, and are exposed to lower pH water more often. By comparing animals in the north with those in the south of the study area, the OMEGAS scientists could effectively peer into the ecosystem’s future. The scientists were substituting space for time.

The California Current Large Marine Ecosystem, showing the sites monitored by OMEGAS for changes in the region’s biology and chemistry. Seawater is coloured according to temperature and land is shown in grey. (Credit: Hoffman et al., 2014)

The California Current Large Marine Ecosystem, showing the sites monitored by OMEGAS for changes in the region’s biology and chemistry. Seawater is coloured according to temperature and land is shown in grey. (Credit: Hoffman et al., 2014)

By matching measurements of ocean properties, including pH, temperature and the amount of CO2 in the water, with information about the way different animals are responding to acidity (e.g. growth rate, shell thickness) and their genetic variation, the team are putting together a picture of how acidification is likely to affect the ecosystem in the future. One such animal is the purple sea urchin, a conspicuously bright spiny mass found throughout the CCLME, and an important control on the amount of algae carpeting the coast.

Purple sea urchin, Strongylocentrotus purpuratus. (Credit: Wikimedia Commons user Taollan83)

Purple sea urchin, Strongylocentrotus purpuratus. (Credit: Wikimedia Commons user Taollan83)

When peering at their skeletons for signs of acidification-related stress, the OMEGAS team found that the urchins differed little between sites – they were all tolerant of the pH range experienced across the CCLME. Urchin larvae travel large distances, rendering populations relatively homogeneous, so it isn’t too surprising. Taking a look at another ecologically important species, the Californian mussel, the team found that they were also made of hardy stuff, as growth in adult mussels was not reduced in low pH regions.

The news wasn’t all good though. A series of complementary experiments revealed that mussel larvae exposed to low pH water showed a decline in both growth and shell strength, similar to that seen in other young marine bivalves. Such a weakness would leave them more susceptible to attack from predators and, as ocean acidification continues, means they will become yet more vulnerable to predation in the future. Purple sea urchin larvae, on the other hand, could tolerate present day CO2 conditions, and higher levels had little influence on their growth and development. What’s more, studies of the sea urchin’s genetics revealed high genetic variation in the purple sea urchin population – a good indicator that they’d be able to adapt to future change.

California mussels, Mytilus californianus. (Credit: Stephen Bentsen)

California mussels, Mytilus californianus. (Credit: Stephen Bentsen)

The study highlights that the impact of acidification varies widely between species and a greater understanding of how ocean acidification will affect a variety of marine organisms is urgently needed. The OMEGAS team are now figuring out the capacity of other organisms in the CCLME to adapt, including coralline algae, a widely distributed algae with a calcium carbonate skeleton, making it highly vulnerable to ocean acidification.

The team are continuing their work in an effort to find refuges that may be relatively safe from future acidification, populations and life stages that are particularly vulnerable and those that are able to adapt to the rate of change our oceans are currently experiencing. Understanding how multiple species can adapt is critical to creating a coherent picture of how acidification will affect regions such as the CCLME in the future.

 

By Sara Mynott, PhD Student, University of Exeter

 

Reference:

Hofmann, G. E., Evans, T. G., Kelly, M. W., Padilla-Gamiño, J. L., Blanchette, C. A., Washburn, L., Chan, F., McManus, M. A., Menge, B. A., Gaylord, B., Hill, T. M., Sanford, E., LaVigne, M., Rose, J. M., Kapsenberg, L., and Dutton, J. M.: Exploring local adaptation and the ocean acidification seascape – studies in the California Current Large Marine Ecosystem, Biogeosciences, 11, 1053-1064, doi:10.5194/bg-11-1053-2014, 2014.

Follow

Get every new post on this blog delivered to your Inbox.

Join other followers: