GeoLog

Ocean Sciences

GeoTalk: A new view on how ocean currents move

GeoTalk: A new view on how ocean currents move

Geotalk is a regular feature highlighting early career researchers and their work. In this interview we speak to Jan Zika, an oceanographer at the University of New South Wales in Sydney, Australia. This year he was recognized for his contributions to ocean dynamics research as the winner of the 2018 Ocean Sciences Division Outstanding Early Career Scientists Award.

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

My pleasure. I was actually pretty set on the geosciences as a kid. I think all my projects in my last year of primary school were about natural disasters of some form or another – volcanoes, earthquakes, tsunamis, etc. My teachers must have thought I was going to grow up to be a villain in a James Bond film.

I grew up in Tasmania, where there aren’t exactly natural disasters, but nature was very present in my everyday life and that sustained my interest into adulthood. When I was ready for university, meteorologists, geologists, and other researchers advised me to do the hard stuff first. So in my undergraduate degree I focused on mathematics and physics. I was good at it, but I kind of forgot why I was there at some point.

Things changed for me when I interned at a marine science laboratory in Hobart operated by the Commonwealth Scientific and Industrial Research Organisation (CSIRO). I’d walked past the building so many times growing up but never thought I’d get to work inside. Bizarrely, I worked on a project related to the Mediterranean Sea. It was just so uplifting being able to put all these skills I had learnt in class, like vector calculus and thermodynamics, into practice.

From then on I was properly hooked on oceanography and the geosciences. I got into a PhD program through the CSIRO, which felt like being drafted to the Premier League. After completing the doctorate, I took a job as a research fellow in Grenoble, France. Not an obvious place to study the ocean I know, but there was a great little team there. After a couple of years, I moved to the UK, first to the University of Southampton then Imperial College London.

After seven years as a research fellow in Europe I returned home to Australia to become, of all things, a mathematics lecturer at the University of New South Wales. My research is still related to oceans and climate, but day-to-day I am teaching maths. At least now when I teach vector calculus I can pepper the lectures with the sorts of applications to the natural world that have inspired me throughout my whole career.

This year you were awarded an Outstanding Early Career Scientists Award in the Ocean Sciences Division at the 2018 General Assembly for you work on understanding the ocean’s thermohaline circulation and its role in Earth’s climate. Could you tell us more about your research in this field and its importance?

I’d love to. In many fields of science just changing the way you look at a problem can have a big effect. Usually this involves drawing different kind of diagrams. These diagrams may seem abstract at first, but eventually they make things easier to understand. Some diagrams we are all familiar with in one way or another, such as the periodic table, Bohr’s model of the atom, and the economists’ cost-benefit curve. These were all, at some stage, new and innovative ways of presenting something fundamentally complex. I am not saying I did anything like make a model for the atom, but I was inspired by the work of 19th century physicists who made simple diagrams to describe thermodynamic systems (like engines and refrigerators, for example). I wanted to apply these types of ideas to the ocean.

Working closely with colleagues in Australia and Sweden, I came up with a way to make a new diagram for the ocean’s thermohaline circulation. This is the circulation that, in part, makes Europe relatively warm, and plays a big role in regulating Earth’s climate. The new diagram we developed helped us to understand the physical processes controlling the thermohaline circulation and opened the door to all sorts of new methods for understanding the ocean’s role in climate.

Jan’s diagram of ocean circulation in temperature-salinity coordinates from a global climate model (Community Earth System Model Version 1). Contours represent volumetric streamfunction in units of Sverdrups (1Sv = 10^6 m^3 s^-1). Credit: Jan Zika

I started to realize I had stumbled onto something really big when I ran the idea by a Canadian colleague Fred Laliberte, who was a researcher at the University of Toronto at the time. He had been working on a very similar problem in the atmosphere, and my diagram was just the thing he needed to work things out. We ended up getting that work published in the journal Science and we were able to say a thing or two about how windy the world might get as the climate changes. To know my ideas were having an impact well beyond my immediate research area really was special.

And what did you find out? How will climate change affect the world’s wind?  

What we found was that overall the earth’s atmosphere won’t get much more energetic (or may even get less energetic) as the climate warms. This means that although extreme storm events may become more frequent in the future, weak storms may become much less frequent (more calm weather). One can draw an analogy with a spluttering engine: it produces bursts of energy when it splutters but is slower and less effective the rest of the time.

Your research pursuits have taken you to some pretty incredible places. What have been some highlights from your time out in the field?

It has been great to balance the mathematics and theory I do with research in the field. As an oceanographer I have been ‘to sea’ a few times. The most memorable was when I was part of a research project to measure in the Southern Ocean. Our research area was between South America and the Antarctic continent. We set off from the Falkland/Malvinas Islands and made our way around the Scotia Sea dropping by South Georgia on our way back. Those Antarctic islands had the most spectacular scenery I have ever seen. The highlight though was when a gigantic humpback whale spent a few hours playing with us and the ship – spinning under water, breaching and popping up to say hello.

Jan (right) with Brian King (left) from the UK National Oceanography Centre. Pictured here on the James Clarke Ross in the South Atlantic deploying an Argo Float. The instrument measures ocean temperature, salinity and pressure. Credit: Jan Zika

As part of the research, we released a small amount of inert substance (a type of chemical that wouldn’t affect marine life) about a kilometre below the surface of the ocean. This is called a ‘tracer.’ The idea was we would let the ocean currents move and stir the substance like milk poured into coffee. It is really important for us to understand how much things mix in the deep ocean as this affects the thermohaline circulation and how heat and carbon are absorbed into the ocean with global warming.

Once we had released the substance it wasn’t that easy to find where it had gone. What we had to do was float around, drop over an instrument that could trap water at different depths, then bring the water samples to the surface and analyse them in a small lab we had on board. The difficult part was the tracer would become really dilute once it had been mixed by ocean currents, and it was both a really time consuming and costly process to collect and analyse the substance. So we had to exploit sophisticated computer models and pool all our knowledge and best guesses on where the tracer might have gone. We did such a good job tracking it that we were able to continue gathering oodles of valuable data for almost twice as long as had originally been planned. This was testament to the excellent teamwork and ingenuity of our collaborators at sea, in the lab and in front of computers.

Outside of research, you have also been involved with a number of science communication initiatives and outreach activities with young students. What advice would you impart to scientists who would like to engage with public audiences?

That is right, I really enjoy inspiring the next generation and getting non-science folk engaged in what we do. I would say that you want to simplify things but don’t dumb them down. I’ve learnt the hard way that even when speaking to other ‘experts’ it is best to use plain language instead of jargon and go slowly through concepts even if you feel they should be basic. I think working with people from around the world (e.g. in France) who don’t have English as a first language, really helped me with this.

Jan teaching a Geophysical Fluid Dynamics class at the University of New South Wales with the aid of a rotating tank experiment. Credit: Susannah Waters

At the same time I am always surprised at how quickly young students can absorb ideas and throw up questions that even an expert wouldn’t have come up with. The great thing is that your students aren’t wedded to dogma like experienced researchers are, and so are capable of much more creative ideas.

The other day I was helping with a special event to encourage females to enter mathematics. I was inspired by a talk given by the Australian Girl’s Maths Olympiad Team who had just competed in Venice. They said solving Maths Olympiad problems was all about breaking down a big problem into smaller problems they already know how to solve. I ended up changing my own talk as I was inspired by this theme.

I guess what I am suggesting is, if you are organising outreach activities, instead of thinking about how to ‘tell them’ how things work, think about ways to get ideas from them. Include them in the process. Ask them the hard questions. That way everyone will be much more involved. And who knows, it might spark a great idea.

Interview by Olivia Trani, EGU Communications Officer

Top ten tourist beaches threatened by tsunamis

Top ten tourist beaches threatened by tsunamis

December 2004 saw one of the deadliest natural disasters in recorded history. 228,000 people were killed when an earthquake off the coast of the Indonesian island of Sumatra triggered tsunami waves up to 30 m high. The destruction was extreme as the waves hit 14 different countries around the Indian Ocean. Economic losses totalled over 10 billion US dollars. The tourism industry in particular suffered a significant blow. In Phuket, a province of Thailand, a quarter of the island’s hotels had closed six months after the tsumani.

“The 2004 Sumatra tsunami and some of the recent Pacific Island tsunamis have shown their devastating impact on beaches and beach-related tourism,” says Andreas Schaefer, a researcher from the Karlsruhe Institute of Technology (KIT). But where is disaster likely to strike next? And can we be prepared for it?

Schaefer and his colleagues are trying to find out. “We asked the question: can we quantify potential tsunami losses to tourism industries along beaches?” he says. The number of tourists visiting the most exotic locations in the world, places such as Thailand, Indonesia, Colombia and Costa Rica, are rising twice as fast as the global average. In some cases, visitor numbers are growing by as much as 11 percent each year.

This rise in tourism in tsunami-prone locations is potentially a cause for real concern. “We compiled the first ever global loss index for the tourism industry [associated with beaches],” continues Schaefer. His findings were presented last month at the European Geosciences Union General Assembly in Vienna .

Beaches can be affected by tsunamis in a variety of ways. As well as the immediate threat to human life, a tsunami wave can leave behind piles of debris or offshore sand that can damage a beach environment. Alternatively, large swathes of beach sand might be removed by erosion. And in cases where an earthquake is very close to the shore, the beach itself may be down-thrust or uplifted during the event, leaving it either permanently submerged underwater or high and dry.

To quantify the locations in the world that are most at risk, Schaefer and his colleagues used two large datasets: tourist information and earthquake statistics.

Tourism-derived GDP per capita across the world. (Image credit: Andreas Schaefer)

To calculate the human exposure, “we compiled a global tourism destination database,” he explains. This database includes over 200 countries, at least 10,000 tourist destinations, more than 24,000 beaches, and almost a million hotels from all around the globe.

“It was important to get the latest and best tourism and hotel information,” says James Daniell, another member of the KIT research team. “Tourism contributes over 6 trillion [US] dollars directly and indirectly to the global economy every year.”

The research team then calculated tsunami probabilities all around the world using earthquake statistics and tectonic modelling. Chile, central America, Indonesia and Japan are the main countries that frequently experience large tsunamis.

Over longer time periods, the Caribbean and Mediterranean are also likely to be affected by rarer events. To put the numbers in perspective, if you spend a day on the coast of Mexico you have a one in 60,000 chance of seeing a tsunami; in Crete, this decreases to one in 600,000.

To model the tsunamis, it is also important to have a good understanding of the shape of the seafloor in the vicinity of the tourist sites. In the deep ocean, big tsunamis can have gaps between waves of as much as 200 km and wave heights as small as 1 m; ships are often unable to feel them passing. But as they approach the shore, the water shallows, causing the waves to slow down and pile up. The wave spacing decreases to less than 20 km, whilst the wave heights can grow to tens of metres. Hence, what looks like an innocuous fluctuation at sea can cause major damage when it reaches land. The depth of the adjacent seafloor plays a major role in this.

Simulated tsunamis across the world showing maximum potential wave heights. (Image credit: Andreas Schaefer)

Given the large number of variables at play, tsunami modelling involves many calculations and typically requires the use of a supercomputer. But in a paper published last year, Schaefer helped to develop a new simulation framework called TsuPy, which allows for quick modelling of tsunamis on personal computers. With this in place, he could rapidly simulate more than 10,000 tsunamis all around the world, calculate the expected wave heights at the tourist sites in his database, and estimate the likely economic losses.

The researchers estimate 250 million US dollars in global annual loss to the tourism industry from tsunami waves. Furthermore, every 10 years they expect a single $1 billion event.

Of all the tourist destinations, “Hawaii is the number one,” says Schaefer. This is “because of all the potential tsunamis that come from around the Pacific Ring of Fire,” he explains. “There are so many [tsunami] sources all around, that, even though they are far away, they have an effect.”

The last major tsunami to strike Hawaii was as a result of the biggest earthquake ever recorded: the 1960 magnitude 9.6 Valdivia earthquake on the coast of Chile. 60 people on Hawaii were killed and the damage amounted to 500 million US dollars in today’s terms.

Top ten locations on the global risk index for beach tourist destinations threatened by tsunamis. (Image credit: Andreas Schaefer)

Other notable locations on the top ten list include Valparaiso (Chile), Bali (Indonesia), and Phuket (Thailand). “Locations that are known for their tourism are at the top of the list because there is a lot [of existing infrastructure] that could be damaged,” explains Schaefer.

Slightly surprisingly, southwest Turkey is also high on the list. Furthermore, places like Tonga and Vanuatu are particularly at risk. They have rapidly developing tourist industries and large projected losses per dollar of tourism-related business, so they feature highly on Schaefer’s list. “They are mostly small island nations with a significant need for tourist dollars,” explains Daniell.

For many parts of the world, the results are not necessarily good news. But they are a first step inasmuch as they highlight the locations that are currently thought to be at greatest risk. “We hope, with these results, to raise awareness among tourists. But they do not need to be afraid,” says Schaefer. With adequate preparation and evacuation planning, it is hoped that future disaster on the scale of the 2004 event might be averted.

By Tim Middleton, EGU 2018 General Assembly Press Assistant

References

Schaefer, A., Daniell, J., and Wenzel, F. Beach Tsunami Risk Modelling – A probabilistic assessment of tsunami risk for the world’s most prominent beaches. Geophysical Research Abstracts, Vol. 20, EGU2018-11955, 2018, EGU General Assembly 2018 (conference abstract)

Schaefer, A. and Wenzel, F. TsuPy: Computational robustness in Tsunami hazard modelling. Computers & Geosciences, 102, 148-157, 2017

Plate Tectonics and Ocean Drilling – Fifty Years On

Plate Tectonics and Ocean Drilling – Fifty Years On

What does it take to get a scientific theory accepted? Hard facts? A strong personality? Grit and determination? For many Earth Scientists today it can be hard to imagine the academic landscape before the advent of plate tectonics. But it was only fifty years ago that the theory really became cemented as scientific consensus. And the clinching evidence was found in the oceans.

Alfred Wegener had proposed the theory of continental drift back in 1912. The jigsaw-fit of the African and South American continents led him to suppose that they must once have been joined together. But in the middle of the century, the idea fell out of favour; some even referred to it as a “fairy-tale”.

It was not until the discovery of magnetic reversals on the seafloor in the early 1960s that the theory began to sound plausible again. If brand new ocean crust was being formed at the mid-ocean ridges, then the rocks either side of the ridge should show symmetrical patterns of magnetism. Fred Vine and Drummond Matthews, geologists at the University of Cambridge in the UK, were the first to publish on the idea of seafloor spreading in 1963.

But plate tectonics was still not the only theory on the market. The expanding Earth hypothesis held that the positions of the continents could be explained by an overall expansion in the volume of the Earth. Numerous twentieth-century physicists subscribed to such a view. Or, similarly, the shrinking Earth theory proposed that the whole planet had once been molten. Mountain ranges would then be formed as the Earth cooled and the crust crumpled.

Helmut Weissert, President of the EGU Stratigraphy, Sedimentology and Palaeontology Division, remembers the difficult exchanges that took place whilst he was a student at ETH Zürich in the late 1960s. “Earth-science-wise it was a hot time,” he recalls. “In Bern University they did not teach plate tectonics. We did not have a course on plate tectonics either. I probably first heard about plate tectonics in [my] second or third year.”

Weissert especially remembers Rudolf Trümpy, professor of Alpine geology at ETH at the time, saying that plate tectonics sounds interesting, but it does not work for the Alps. Meanwhile, younger voices at ETH, postdocs and lecturers, were becoming increasingly convinced by plate tectonic theory.

Weissert soon found himself in the midst of the controversy as his own research had a direct bearing on the debate. “I had an interesting diploma topic,” says Weissert. “I worked on continental margin successions and associated serpentinites.” Serpentinites are green-coloured rocks that are full of the water-rich mineral serpentine, and therefore must have formed on the ocean floor. The fact that Weissert was finding them in Davos, at the top of the Alps, was a good indication that modern-day Switzerland had once been part of the oceans. As Weissert succinctly puts it, “green rocks were ocean”.

The observed and calculated magnetic profile for the seafloor across the East Pacific Rise, showing symmetrical patterns of magnetism. (Image Credit: U.S. Geological Survey. Distributed via Wikimedia Commons)

By 1967, interest in the theory of plate tectonics had snowballed. When the Deep Sea Drilling Project (DSDP) was launched the following year, it had its sights firmly set on finding evidence that would definitively either confirm or reject the hypothesis of seafloor spreading.

The DSDP research vessel, the Glomar Challenger, set sail from Texas in March 1968. By its third leg it had drilled 17 holes at 10 sites along the mid-Atlantic ocean ridge and was already producing results that looked like they would confirm Wegener’s theory of continental drift. “After a few legs it was clear that the seafloor spreading hypothesis was tested and proven,” remembers Weissert.

There were only eight scientists on board, but two or three of them were working on the stratigraphy of the seafloor sediments. “The stratigraphy was superb,” explains Weissert. “You have the very young [sediments near the ridge] and then at the edges of the ocean the Jurassic sediments. If you have aging crust then you have aging sediment, so the hypothesis was very clear.” If the sediments got progressively older on moving away from the ridge, then so must the crust, a sure sign that new ocean floor was being created at the ridge.

Karen Heywood, EGU Division President in Ocean Sciences, remembers how her own fascination with the theory of plate tectonics ended up sparking her career in physical oceanography. Heywood began as a physics student at the University of Bristol in the 1980s. “They said we had to write an essay on the historical development of an idea in physics,” she recalls. “I did the development of the theory of plate tectonics and seafloor spreading. I wrote this essay all about Alfred Wegener.”

“This essay inspired me to think about earth sciences,” she says. “The idea that you could apply physics to the real world was amazing. It got me into oceanography.”

Heywood went on to establish her career at the University of East Anglia (UEA), where she became the first female professor of Physical Oceanography in the UK. “I went to the UEA and Fred Vine was there. It brought me back full circle. I could not believe that this was Fred Vine, who had discovered the magnetic stripes. This was the real person and that was amazing… it was the same person that I had read about and written about in my essay as an undergraduate in the 80s.”

There were clearly strong personalities on both sides of the debate about plate tectonics, but Weissert is pragmatic about the progress of science. “You have to accept that you are part of a scientific development. Everybody makes hypotheses… We all make mistakes. We all learn. We all improve.”

Indeed, many years later, in 2001, Trümpy wrote what Weissert calls “a beautiful small article” entitled Why plate tectonics was not invented in the Alps. Trümpy magnanimously writes, “Shamefacedly, I must admit that I was not among the first Alpine geologists to grasp the promise of the new tectonics.”  And yet, he continues, “to the Alps, plate tectonics brought a better understanding”. The humans and the science move on together.

By Tim Middleton, EGU 2018 General Assembly Press Assistant

References

DSDP Phase: Glomar Challenger, International Ocean Discovery Program

Trümpy, R., Why plate tectonics was not invented in the Alps, International Journal of Earth Sciences, Volume 90, Issue 3, pp 477–483, 2001.

Underwater robot shares ocean secrets

Underwater robot shares ocean secrets

Buoyancy-driven drones are helping scientists paint a picture of the ocean with sound.

Around the world, silent marine robots are eavesdropping on the ocean and its inhabitants. The robots can travel 1000 metres beneath the surface and cover thousands of kilometres in a single trip, listening in on the ocean as they go.

These bright yellow bots, known as Seagliders, are about the size of a diver, but can explore the ocean for months on end, periodically relaying results to satellites.

Researchers have been utilising gliders for about 20 years, first using them to measure temperature and salinity. But over time, scientists have expanded their capabilities and now they can record ocean sounds.

You can learn a lot from the recordings if you know how to read them. The background noise is produced by high winds, the low frequency rumble comes from moving ships, and the punctuating whistles and clicks are produced by different marine species.

Sperm whale and dolphin echolocation clicks. Every two seconds you hear a loud click, the sound of a sperm whale. The more rapid clicks correspond to dolphins. Credit: University of East Anglia

Pierre Cauchy, a PhD researcher from the University of East Anglia, UK, has been using seagliders to create an underwater soundscape across the Mediterranean, Atlantic and Southern Oceans. He presented his latest findings at the EGU General Assembly in Vienna last week.

Here in the ocean, the nights can be noisier than the days. When the sun goes down, fish sing out in chorus, a sound that rings out at 700 Hz. “I wasn’t expecting that, it was serendipitous,” says Cauchy. It’s not only fish that can be picked up by the gliders; dolphins and whales make characteristic whistles and clicks, meaning species can be identified from their vocal patterns alone.

The next step is to cross check the recordings with others made in the area, and confirm which species he’s been listening to. In the future, Cauchy hopes the technology will be used to monitor changes in ecosystem health over time.

While it’s hard to know what a healthy ecosystem sounds like, you can monitor the same spot from year to year and work out whether it is healthier, or less healthy than it was previously. A more healthy ecosystem may be filled with the sounds of different fish, and other species, representing a diverse, species-rich habitat.. A less healthy one would be quiet, or more monotonous.

Pod of long-finned pilot whales in the North Atlantic. Credit: University of East Anglia

The sound of a pod of pilot whales – bright areas indicate bursts of sound at a particular frequency. The patterns and frequencies differ for each species. Credit: Cauchy et al. (2008).

Scientists could also use gliders to fill gaps in our understanding of extreme weather around the world, especially in places where collecting data is a challenge, like the high seas. “That’s the good thing with gliders, you can send them where data is needed,” emphasises Cauchy.

Researchers have been using satellite data to validate wind speed models and map weather events like hurricanes, but even satellites need to be calibrated against measurements made on the Earth’s surface. The seagliders can do just that; hydrophones pick up wind at two to 10 kilohertz and the faster the wind, the louder the sound. “The more in-situ data you have, the better your satellite data is, and that’s better for the models,” Cauchy explains.

Future work could see scientists sending gliders into hurricanes to measure wind speeds reached during extreme weather events.

By Sara Mynott

References

Cauchy, P. Passive Acoustic Monitoring from ocean gliders. EGU General Assembly. 2018. 

EGU General Assembly press conference recording available here.