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Imaggeo on Mondays: Isolated atoll

Imaggeo on Mondays: Isolated atoll

Covering a total area of 298 km², the idylic natural atolls and reefs of the Maldives stretch across the Indian Ocean. The tropical nation is famous for it’s crystal clear waters and picture perfect white sand beaches, but how did the 26 ring-shaped atolls and over 1000 coral islands form?

Coral reefs commonly form immediately around an island, creating a fringe which projects seawards from the shore. If the island is of volcaninc origin and slowly subsides below sea level, while the coral continues to grow growing outwards and upwards, an atoll is formed. They are usually roughly circular in shape and have a central lagoon. If the coral reef grows high enough, it will emerge from the sea waters and start to form a  tiny island.

“I took this photo while flying over the Maldives, south of Malè, from a small seaplane,” describes Favaro, who took this stunning aerial image of an atoll above the Indian Ocean.

Pictured, goes on to explain Favaro,

“[is] part of the ring-shaped coral reef bounding the atoll. On the right side of the image there is the lagoon and on the left side the open ocean. The coral reef is interrupted twice by ‘Kandu’ (water passages in Dhivehi [the language spoken in the Maldives]), which are the places where water flows in and out of the atoll when the tides changes”.

Two small harbours and antennas suggest the two small islands are occupied by local people, not by a resort or hotels.

“What always strikes me is how they can live so isolated, in a place which doesn’t offer basic resources, such as drinkable water,” says Favaro.

Fresh water is scarce in this archipelago nation. Rainwater harvesting is unreliable; poor rainfall means depleted collection tanks and groundwater tables. The problem is being exacerbated by climate change which is altering the monsoon cycle and rainfall patters over the Indian Ocean. As a result, the country relies heavily on desalination plants (and imported bottled water) to sustain the nation and the 1 million tourists who visit annually.

This animation shows the dynamic process of how a coral atoll forms. Corals (represented in tan and purple) begin to settle and grow around an oceanic island forming a fringing reef. It can take as long as 10,000 years for a fringing reef to form. Over the next 100,000 years, if conditions are favorable, the reef will continue to expand. As the reef expands, the interior island usually begins to subside and the fringing reef turns into a barrier reef. When the island completely subsides beneath the water leaving a ring of growing coral with an open lagoon in its center, it is called an atoll. The process of atoll formation may take as long as 30,000,000 years to occur. Caption and figure credit: National Oceanographic and Atmospheric Administration (NOAA).

References and further reading

How Do Coral Reefs Form? An educational resource by NOAA

Amazing atolls of the Maldives – a feature on NASA’s Earth Observatory.

 

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/.

 

GeoSciences Column: Catch of the day – what seabirds can tell us about the marine environment

GeoSciences Column: Catch of the day – what seabirds can tell us about the marine environment

Off the coast of Germany, a male northern gannet (for ease, we’ll call him Pete) soars above the cold waters of the North Sea. He’s on the hunt for a shoal of fish. Some 40km due south east, Pete’s mate and chick await, patiently, for him to return to the nest with a belly full of food.

Glints of silver just below the waves; the fish have arrived.

Pete readies himself.

Body rigid, wings tucked in close – but not so close that he can’t steer himself – he dives toward the water at a break-neck speed, hitting almost 100 km per hour. Just as he is about to hit the water, Pete folds his wings, tight, against his body. He pierces the water; straight as an arrow, fast as a bullet, and makes his catch.

The first of the day.

He’ll continue fishing for the next 8 to 10 hours.

As he does so, a tiny logger weighing no more than 48 g, will continually track Pete’s position and with every dive, the temperature of the sea water.

Why equip birds with sensors?

The physical properties of the oceans, such as water temperature, play an important role in determining where organisms are found in the vastness of the oceans. Life tends to concentrate in regions where there are temperature changes, be that as waters get deeper or across large horizontal distances.

Sea surface temperatures also reveal vital information about the global climate system, as they help scientists understand how the oceans are connected to the atmosphere. The data are used in weather forecasts and simulations of how the Earth’s atmosphere changes over time.

By mounting light-weight loggers on diving mammals (it needn’t be only birds, seals and penguins are good candidates too), scientists can learn a lot from the animal’s behaviour, while at the same time collecting data about the physical properties of the oceans.

That is why a German research team, led by Stefan Garthe of the Research & Technology Centre (FTZ) at Kiel University, has been tagging and monitoring the behaviour of a colony of northern gannets breeding on the German island of Heligoland. As a top marine predator, changes in the foraging behaviour of gannets can indicate changes in food resources, often linked to variations in the marine environment.

Flying northern gannets with a Bird Solar GPS logger attached to the tail feathers. Photo: K. Borkenhagen. From Garthe S., et al. 2017.

Their work is part of a larger project called The Coastal Observing System for Northern and Arctic Seas, or COSYNA for short, which aims to better understand the complex interdisciplinary processes of northern seas and the Arctic coasts in a changing environment.

The German Bight

The waters of the northern seas and Arctic coasts are governed by a large range of natural processes and variables, such as wind, sea surface temperature and tides. In addition, the North Sea in particular, is heavily used for human activities: from shipping, to tourism, through to exploitation (and exploration) of food resources, energy and raw materials – making it of huge economic value and importance.

But it is precisely this heavy human activity which is contributing to change and disruptions in the region. Scientists know that the biochemistry, food webs, ecosystems and species of the North Sea are being altered. However, the causes of the change aren’t well quantified or understood and their consequences poorly defined. This means mitigating and adapting to the changes is proving hard for scientists and policy-makers alike.

Where progress and nature collide

In an area so heavily influenced by anthropogenic activities, it’s not unlikely that observed changes to the properties of the waters of the North Sea and the German Bight (where Heligoland is located) are driven, to some extent, by human actions.

Since 2008, 12 offshore wind farms have become operational in the German Bight and a further five are under construction; 15 more have been given building consent too. However, what impact (if any) wind farms have on seabirds is a hotly debated topic. Their effect on the hydrodynamics, biogeochemistry and biology of the North Sea is also poorly understood.

To unravel some of these questions, Garthe and his team tracked the movements of three individual gannets near existing wind farms in the North Sea. To find out their exact position, a GPS (mounted on the bird’s tail) was used and the flight tracks plotted on a map which also displayed the wind farms of the German Bight.

Overlap of flight patterns for the three northern gannets shown with the locations of wind farms in the German Bight. From Garthe S., et al. 2017.

Their results, published in the EGU’s open access journal Ocean Science, show that all three birds largely avoided the three wind farms just north of Heligoland. Though they visited sporadically, more often than not, the gannets flew around wind farms which also happened to be further away from their breeding grounds.

The team will now use the data acquired, which is of a much higher resolution than what has been available before, to understand how wind farms in the North Sea are affecting long-term seabird behaviour.

By Laura Roberts Artal, EGU Communications Officer.

References and further reading

Garthe, S., Peschko, V., Kubetzki, U., and Corman, A.-M.: Seabirds as samplers of the marine environment – a case study of northern gannets, Ocean Sci., 13, 337-347, https://doi.org/10.5194/os-13-337-2017, 2017.

Baschek, B., Schroeder, F., Brix, H., Riethmüller, R., Badewien, T. H., Breitbach, G., Brügge, B., Colijn, F., Doerffer, R., Eschenbach, C., Friedrich, J., Fischer, P., Garthe, S., Horstmann, J., Krasemann, H., Metfies, K., Merckelbach, L., Ohle, N., Petersen, W., Pröfrock, D., Röttgers, R., Schlüter, M., Schulz, J., Schulz-Stellenfleth, J., Stanev, E., Staneva, J., Winter, C., Wirtz, K., Wollschläger, J., Zielinski, O., and Ziemer, F.: The Coastal Observing System for Northern and Arctic Seas (COSYNA), Ocean Sci., 13, 379-410, https://doi.org/10.5194/os-13-379-2017, 2017.

Why do scientists measure sea surface temperature? (NOAA)

Scientists are putting seals to work to gather ocean current data (PRI)

Daunt, F., Peters, G., Scott, B., Grémillet, D., and Wanless, S.: Rapid-response recorders reveal interplay between marine physics and seabird behaviour, Mar. Ecol.-Prog. Ser., 255, 283–288, 2003.

Grémillet, D., Lewis, S., Drapeau, L., van der Lingen, C. D.,Huggett, J. A., Coetzee, J. C., Verheye, H. M., Daunt, F.,Wanless, S., and Ryan, P. G.: Spatial match–mismatch in the Benguela upwelling zone: should we expect chlorophyll and sea-surface temperature to predict marine predator distributions?, J. Appl. Ecol., 45, 610–621, 2008.

Wilson, R. P., Grémillet, D., Syder, J., Kierspel, M. A. M., Garthe, S., Weimerskirch, H., Schäfer-Neth, C., Scolaro, J. A., Bost, C.- A., Plötz, J., and Nel, D.: Remote-sensing systems and seabirds: their use, abuse and potential for measuring marine environmental variables, Mar. Ecol.-Prog. Ser., 228, 241–261, 2002.

GeoTalk: The anomaly in the Earth’s magnetic field which has geophysicists abuzz

GeoTalk: The anomaly in the Earth’s magnetic field which has geophysicists abuzz

Geotalk is a regular feature highlighting early career researchers and their work. In this interview we speak to Jay Shah, a PhD student at Imperial College London, who is investigating the South Atlantic Anomaly, a patch over the South Atlantic where the Earth’s magnetic field is weaker than elsewhere on the globe. He presented some of his recent findings at the 2017 General Assembly.

First, could you introduce yourself and tell us a little more about your career path so far?

I’m currently coming to the end of my PhD at Imperial College London. For my PhD, I’ve been working with the Natural Magnetism Group at Imperial and the Meteorites group at the Natural History Museum, London to study the origin of magnetism in meteorites, and how meteoritic magnetism can help us understand early Solar System conditions and formation processes.

Before my PhD I studied geology and geophysics, also at Imperial, which is when I studied the rocks that I spoke about at the 2017 EGU General Assembly.

What attracted you to the Earth’s magnetic field?

Jay operates the Vibrating Sample Magnetometer at the lab at Imperial. Credit: Christopher Dean/Jay Shah

My initial interest in magnetism, the ‘initial spark’ if you like, was during my undergraduate, when the topic was introduced in standard courses during my degree.

The field seemed quite magical: palaeomagnetists [scientists who study the Earth’s magnetic field history] are often known as palaeomagicians. But it’s through rigorous application of physics to geology that palaeomagicians can look back at the history of the Earth’s magnetic field recorded by rocks around the world. I was attracted to the important role palaeomagnetism has played in major geological discoveries such as plate tectonics and sea-floor spreading.

Then, during my undergraduate I had the opportunity to do some research alongside my degree, via the ‘Undergraduate Research Opportunities Programme’ at Imperial. It was certainly one of the bonuses of studying at a world-class research university where professors are always looking for keen students to help move projects forward.

I was involved in a project which focused on glacial tillites [a type of rock formed from glacial deposits] from Greenland to look into inclination shallowing; which is a feature of the way magnetism is recorded in rocks that can lead to inaccurate calculation of palaeolatitutdes [the past latitude of a place some time in the past]. Accurate interpretation of the direction of the Earth’s magnetic field recorded by rocks is essential to reconstructing the positions of continents throughout time.

This was my first taste of palaeomagnetism and opened the doors to the world of research.

So, then you moved onto a MSci where one of your study areas is Tristan da Cunha, a volcanic island in the South Atlantic. The location of the island means that you’ve dedicated some time to studying the South Atlantic Anomaly (SAA). So, what is it and why is it important?

The SAA is a present day feature of the magnetic field and has existed for the past 400 years, at least, based on observations. It is a region in the South Atlantic Ocean where the magnetic field is weaker than it is expected to be at that latitude.

The Earth’s magnetic field protects the planet and satellites orbiting around Earth from charged particles floating around in space, like the ones that cause aurorae. The field in the SAA is so weak that space agencies have to put special measures in place when their spacecraft orbit over the region to account for the increased exposure to radiation. The Hubble telescope, for example, doesn’t take any measurements when it passes through the SAA and the International Space Station has extra shielding added to protect the equipment and astronauts.

If you picture the Earth’s magnetic field:  it radiates from the poles towards the Earth’s equator, like butterfly wings extending out of the planet. In that model, which is what palaeomagnetic theory is based on, it is totally unexpected to have a large area of weakness.

Earth’s magnetic field connects the North Pole (orange lines) with the South Pole (blue lines) in this NASA-created image, a still capture from a 4-minute excerpt of “Dynamic Earth: Exploring Earth’s Climate Engine,” a fulldome, high-resolution movie. Credit: NASA Goddard Space Flight Center

We also know that the Earth’s magnetic field reverses (flips its polarity), on average, every 450,000 years. However, it has been almost twice as long since we have had a flip, which means we are ‘overdue’ a reversal. People like to look for signs that the field will reverse soon; could it be that the SAA is a feature of an impending (in geological time!) reversal? So, it becomes important to understand the SAA in that respect too.

So, how do you approach this problem? If the SAA is something you can’t see, simply measure, how do you go about studying it?

Palaeomagnetists can look to the rock record to understand the history of the Earth magnetic field.

Volcanic rocks best capture Earth’s magnetic field because they contain high percentages of iron bearing minerals, which align themselves with the Earth’s magnetic field as the lavas cool down after being erupted. They provide a record of the direction and the strength of the magnetic field at the time they were erupted.

In particular, I’ve been studying lavas from Tristan da Cunha (a hotspot island) in the Atlantic Ocean similar in latitude to South Africa and Brazil. There are about 300 people living on the island, which is still volcanically active. The last eruption on the island was in 1961. In 2004 there was a sub-marine eruption 24 km offshore.

Jürgen Matzka (GFZ Potsdam) collected hundreds and hundreds of rock cores from Tristan da Cunha on sampling campaigns back in 2004 and 2006.

We recently established the age of the lavas we sampled as having erupted some 46 to 90 thousand years ago. Now that we know the rock ages, we can look at the Earth’s magnetic field during this time window.

Why is this time window important?

These lavas erupted are within the region of the present day SAA, so we can look to see whether any similar anomalies to the Earth’s magnetic field existed in this time window.

So, what did you do next?

When Jurgen looked at the samples, he too was trying to find something out about the SAA, but the samples reviled nothing.

Initial analyses of these rocks focused on the direction of the magnetic field recorded by the rocks. The directional data can be used to trace back past locations of the Earth’s magnetic poles.

Then, during my master’s research dissertation I had the opportunity to experiment on the rocks from Tristan da Cunha with the focus on palaeointensity [the ancient intensity of the Earth’s magnetic field recorded by the rocks]. We found that they have the same weak signature we observe today in the SAA but in this really old time window.

The rocks from Tristan da Cunha, 46 to 90 thousand years ago, recorded a weaker magnetic field strength compared to the strength of the magnetic field of the time recorded by other rocks around the world.

Some of the lavas sampled on Tristan da Cunha. Credit: Jürgen Matzka

What does this discovery tell us about the SAA?

I mentioned at the start of the interview that, as far as we thought, the anomaly didn’t extend back more than 400 years ago – it’s supposed to be a recent feature of the field. Our findings suggest that the anomaly is a persistent feature of the magnetic field. Which is important, because researchers who simulate how the Earth’s magnetic field behaved in the past don’t see the SAA in simulations of the older magnetic field.

It may be that the simulations are poorly constrained. There are far fewer studies (and samples) of the Earth’s magnetic directions and strengths from the Southern Hemisphere. This inevitably leads to a sampling bias, meaning that the computer models don’t have enough data to ‘see’ the feature in the past.

However, we are pretty certain that the SAA isn’t as young as the simulations indicate. You can also extract information about the ancient magnetic field from archaeological samples. As clay pots are fired they too have the ability to record the strength and direction of the magnetic field at the time. Data recorded in archaeological samples from southern Africa, dating back to 1250 to 1600 AD also suggest the SAA existed at the time.

Does the fact that the SAA is older than was thought mean it can’t used be to indicate a reversal?

It could still be related to a future reversal – our findings certainly don’t rule that out.

However, they may be more likely to shed some light on how reversals occur, rather than when they will occur.

It’s been suggested that the weak magnetic anomaly may be a result of the Earth’s composition and structure at the boundary between the Earth’s core and the mantle (approximately 3000 km deep, sandwiched between the core and the Earth’s outermost layer known as the crust). Below southern Africa there is something called a large low shear velocity province (LLSVP), which causes the magnetic flux to effectively ‘flow backwards’.

These reversed flux patches are the likely cause of the weak magnetic field strength observed at the surface, and could well indicate an initiating reversal. However, the strength of the Earth’s magnetic field on average at present is stronger than what we’ve seen in the past prior to field reversals.

The important thing is the lack of data in the southern hemisphere. Sampling bias is pervasive throughout science, and it’s been seen here to limit our understanding of past field behaviour. We need more data from around the world to be able to understand past field behaviour and to constrain models as well as possible.

Sampling bias is pervasive throughout science, and it’s been seen here to limit our understanding of past field behaviour. This image highlights the problem (black dots = a sampling location). Modified from an image in the supporting materials of Shah, J., et al. 2016. Credit: Jay Shah.

You are coming towards the end of your PhD – what’s next?

So I moved far away from Tristan da Cunha for my PhD and have been looking at the magnetism recorded by meteorites originating from the early Solar System. I’d certainly like to pursue further research opportunities working with skills I’ve gained during my PhD. I want to continue working in the magical world of magnetism, that’s for sure! But who knows?

Something you said at the start of the interview struck me and is a light-hearted way to round-off our chat. You said that palaeomagnetism are often referred to as ‘paleaomagicians’ by others in the Earth sciences, why is that so?

Over the history of the geosciences, palaeomagntists have contributed to shedding light on big discoveries using data that not very many people work with. It’s not a big field within the geosciences, so it’s shrouded in a bit of mystery. Plus, it’s a bit of a departure from traditional geology, as it draws so heavily from physics. And finally, it’s not as well established as some of the other subdisciplines within geology and geophysics, it’s a pretty young science.  At least, that’s why I think so, anyway!

Interview by Laura Roberts Artal, EGU Communications Officer

References and further reading

Shah, J., Koppers, A.A., Leitner, M., Leonhardt, R., Muxworthy, A.R., Heunemann, C., Bachtadse, V., Ashley, J.A. and Matzka, J.: Palaeomagnetic evidence for the persistence or recurrence of geomagnetic main field anomalies in the South AtlanticEarth and Planetary Science Letters441, pp.113-124, doi: 10.1016/j.epsl.2016.02.039, 2016.

Shah, J., Koppers, A.A., Leitner, M., Leonhardt, R., Muxworthy, A.R., Heunemann, C., Bachtadse, V., Ashley, J.A. and Matzka, J.: Paleomagnetic evidence for the persistence or recurrence of the South Atlantic geomagnetic Anomaly. Geophysical Research Abstracts, Vol. 19, EGU2017-7555-3, 2017, EGU General Assembly 2017.

Imaggeo on Mondays: What happens to mines when they become redundant?

Imaggeo on Mondays: What happens to mines when they become redundant?

When the minerals run out, or it is no longer profitable to extract the resources, mines shut down. Prior to issuing a permit for the exploitation of a resource, most regulators require assurance that once the mine closes it, or the activities carried out at the site, will not present a risk to human health or the environment.

Ongoing monitoring of a mine once it is decommissioned is required to ensure this is the case.

“The goal of my work is to study the environmental impact of mining waste in the north-east part of Algeria,” explains Issaad Mouloud, author of today’s featured image.

Algeria has a long history of mining. Since the antiquity and the time of the Berbers, many minerals and ores deposits were exploited. The northeast was the most productive region in the country. The geology of the study area is composed of magmatic and metamorphic rocks, sandstone and limestone.

Kef Oum Theboul mining district is located on the Eastern cost of Algeria, 4 km west of the Tunisian border. It is located 15 km from the town of El Kala. The Kef Oum Theboul site covers an area of 26.6 km2 and which contains copper lead and zinc ore

Discovered in 1845, the Kef Oum Teboul ore deposits were mined from 1849 to the 1970s. The Messida ore plant, pictured above and located not far from the Kef Oum Teboul deposit, is one of Issaad’s study sites.

The ore plant, situated in the Algerian Mediterranean coast, on Messida beach (located 6km from Kef Oum Teboul) processed copper, lead and zinc mineralizations.  Processing at the plant started in 1899.  It had three water jacket furnaces, with a capacity of 50 tons of ore per 24 hours. The obtained matte contained 20-22% copper, 200 grams of silver and 11-12 grams of gold per ton.

“The plant is now totally destroyed but mining waste, mainly sulphur ore and slag, is still stored in the Messida area,” explains Issaad, who goes on to say “the main pollution factor which I study is the acid mine drainage and heavy metals.”

 

Abandoned sulphurous ore and slag stored in the ruins of the ore processing plant of Messida. Credit: Issaad Mouloud

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/.

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