GeoLog

ocean sciences

Imaggeo on Mondays: Monitoring Antarctica’s ocean current

Imaggeo on Mondays: Monitoring Antarctica’s ocean current

This week’s featured image depicts a quiet and still oceanic landscape in Antarctica, but polar scientists are studying how energetic and variable the ocean currents in this part of the world can be.

In this picture, the marine research vessel RRS James Clark Ross is making its way through the Lemaire Channel, a small passage off the coast of the Antarctic Peninsula, south of the southernmost tip of Chile. This channel is about 11 kilometres long and just 1,600 metres wide at its narrowest point, bordered by a spectacular range of steep cliffs.

At the time this photo was taken, the ship was headed to the Rothera Research Station, a British Antarctic Survey base on the white continent’s peninsula. The scientists aboard the vessel are part of a decades-long research campaign surveying the ocean current surrounding Antarctica, known as the Antarctic Circumpolar Current (ACC). The ACC is the world’s strongest and most influential current, transporting 165 million to 182 million cubic metres of water every second and connecting most of Earth’s major oceans. As such, any changes to the ACC have the potential to impact other marine environments around the world.

For more than 25 years, scientists from the UK’s National Oceanography Centre (NOC) have ventured south each Antarctic summer to measure the ocean’s physical features in one region of the Southern Ocean, called the Drake Passage. Spanning just 800 kilometres between the Falkland Islands and the Antarctic Peninsula, the Drake Passage is the shortest crossing from Antarctica to any other landmass. This makes it a prime spot to survey the ocean’s currents, as the flow is constricted to a narrow geographical region.

So far, researchers have completed 24 survey trips across the passage. The data collected during these trips have been used to assess how physical features of the ACC change, both throughout a single year and over the course of several years. Yvonne Firing at NOC leads the latest expeditions as part of the UK funded ORCHESTRA project. The continuation of this monitoring is helping scientists study how the ocean stores excess heat and carbon. No other ocean basin has been monitored so consistently, making the Drake Passage the most comprehensively studied part of the Southern Ocean.

By Olivia Trani, EGU Communications Officer

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/.

Imaggeo on Mondays: Recreating monster waves in art and science

Imaggeo on Mondays: Recreating monster waves in art and science

Featured in this blog post is a collection of images that gives a picture-perfect example of life imitating art.

The photos in the left column are three consecutive still frames of a breaking wave that scientists generated in a lab environment at the University of Edinburgh in the UK. The pictures in the centre and right columns show the same wave images, but now superimposed with the famous 19th century Japanese woodblock print, The Great Wave off Kanagawa.

While the images were produced on opposite sides of the Earth with a few hundreds of years between their creation, the curves and edges of the waves are very similarly positioned.

“Completely coincidentally, in a strange twist of fate, the wave we created bears striking resemblance to The Great Wave off Kanagawa, painted many years ago by the Japanese artist Katsushika Hokusai,” said Mark McAllister, a researcher at the University of Oxford in the UK. He is part of a team of scientists working to better understand the dynamics of freak waves – waves that are unexpectedly large in comparison to the waves that surround it.

The images also highlight the similarities between artists and scientists that often are overlooked: while art and science are different in many ways, both involve observing and trying to interpret their surroundings. The wave simulation photos and the woodblock print both visualise a common endeavor: recreating nature to better understand it.

Simulating monster waves

The photographs in the left column feature the recreation of a very particular wave that took form in 1995 in the North Sea, known as the Draupner freak wave. This particular surface wave was one of the first confirmed observations of a freak wave at sea. The Draupner Oil Platform had taken measurements of the event, reporting that the wave was 26 metres tall (more than twice as tall as the surrounding waves). Rogue waves as high as 30 metres had been reported by sailors and scientists for many years, but until the 20th century there was wide disbelief from the scientific community that such waves were more than myth.

“The measurement of the Draupner wave in 1995 was a seminal observation initiating many years of research into the physics of freak waves and shifting their standing from mere folklore to a credible real-world phenomenon,” said McAllister in a recent press release.

Such rogue waves are capable of causing heavy damage to large ships, and by recreating the Draupner freak wave, McAllister and his colleagues are trying to better understand how this marine phenomenon occurs.

Experiments were carried out in the FloWave Ocean Energy Research facility at the University of Edinburgh. The facility has a circular basin equipped with wavemakers around the entire circumference, allowing scientists to generate waves from any direction and recreate complex wave conditions.

The research team was able to simulate this wave on a smaller scale by crossing two different wave groups at a large angle. They found that when the two wave groups hit each other at 120 degrees, this allowed the freak wave to take shape.

Typically, wave breaking in the ocean limits the maximum height of waves. But when waves cross each other at large angles, wave breaking behaviour changes, removing typical height limitations.

Monster wave immortalised in print

The Great Wave off Kanagawa, one of Hokusai’s most famous prints, depicts three crewed boats at sea, seemingly seconds away from crashing into a monstrous wave, with Japan’s Mount Fugi sitting in the distance. The work is often interpreted to symbolize the eternity and formidable force of nature compared to the frailty of humans.

While the print is often considered to be an artistic representation of a tsunami, one study argues that the features and conditions are more similar to a freak wave event. By using the boats and the mountains as reference points, the researchers involved in the study estimate that the great wave is approximately 10-12 metres in height.

While many artists distort reality to enhance and highlight certain aspects of their work, the researchers point out that Hokusai’s work is likely to be representative of nature, noting that he strove for years to understand the structure of his surroundings and draw them accurately in his art. In the afterward of his 1834 collection of prints containing The Great Wave of Kanagawa, Hokusai writes:

“Since the age of six, I had a habit of sketching from life. From fifty onwards I began producing a fair amount of art work, but nothing I did before the age of seventy was worthy of attention. At seventy-three, I began to grasp the structures of birds and beasts, insects and fish, and of the way plants grow.

If only I go on trying, I will surely understand them still better by the time I am eighty, so that by ninety I will have penetrated to their essential nature. At one hundred, I hope I may have a divine understanding of them, while at one hundred and ten I may have reached the stage where every dot and every stroke I paint will be alive. May men of great age and virtue see that I am not hoping for too much!”

By Olivia Trani, EGU Communications Officer

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/.

Back for the first time: measuring change at Narrabeen–Collaroy Beach

Back for the first time: measuring change at Narrabeen–Collaroy Beach

Narrabeen–Collaroy Beach in New South Wales, Australia, just north of Sydney, is home to one of the longest-running shoreline-measurement programmes in the world. With colleagues at the University of New South Wales (UNSW) Sydney, Eli Lazarus, an associate professor in geomorphology at the University of Southampton, UK, has been analysing over 40 years of data from Narrabeen–Collaroy to better understand how shorelines recover from major storm events.

In this blog post, Lazarus shares a glimpse of the programme’s history and describes his experience of visiting a field site that for him is both familiar and brand new.

“Want to see what an old GPS unit looks like after it’s been up and down the beach a thousand times?”

Mitchell Harley, a Scientia Fellow and coastal researcher at the UNSW Sydney Water Research Laboratory (WRL), in Manly Vale, Australia, handed me a battered, corroded, steel-cased receiver the size of a grapefruit. “It’s also seen a lot of Duct Tape.”

He loaded a carbon-fibre survey staff and a yellow Pelican case containing a new, a top-of-the-line Trimble GPS handset into the back of a WRL vehicle. With two visiting masters students – Tim van Dam from TU Delft, and Yann Larré from École Polytechnique – we set off on our afternoon excursion, to Narrabeen.

View of Narrabeen Beach, looking south from Narrabeen Headland. Credit: Eli Lazarus

Facing the open South Pacific, Narrabeen and Collaroy are the northern and southern halves of an embayed beach, a reach of sand framed at either end by rocky promontories, that extends approximately three-and-a-half kilometres between Narrabeen Headland and Long Reef Point. Narrabeen is the keystone of the Northern Beaches, a chain of sandy pockets defining the coastal peninsula north of Sydney. The beaches darken in colour with each embayment, from dun in the south to a reddish ochre in the north, representative of the ancient sandstone bedrock units in which they sit.

Narrabeen is a legendary surf break and home turf to a roll of world champions, where, to date, the locals have successfully prevented the installation of anything that resembles a surf cam. But the beach is also home to one of the longest-running and most complete beach-survey programmes in the world (Turner et al., Sci Data 2016).

In 1976, the renowned coastal scientist Andy Short, who used to live in Narrabeen, began the programme from the beach across the street from his house. He and family members, colleagues, friends, and volunteers diligently measured a set of cross-shore profiles along the full Narrabeen–Collaroy embayment every month for 30 years.

All long-term monitoring endeavours are labours of love. But frequent, detailed measurements of beach morphology, maintained consistently over long time scales, are exceptionally rare, and they offer essential quantitative insight into coastal events, changes, and cycles that occur more rapidly than most records tend to capture.

Harley took over the measurement programme in 2006, along with Ian Turner, who now directs the Water Research Lab, and recorded more than 120 monthly surveys of the full beach with a quad-bike Harley would trailer back and forth from Manly Vale.

Harley’s quad-bike – and shoreline-survey workhorse – at the UNSW Sydney Water Research Lab. Credit: Eli Lazarus

The Water Research Laboratory team has continued to experiment with different measurement methods for the Narrabeen–Collaroy system. Mounted on the top floor of the Flight Deck, a beachfront hotel where Narrabeen blends into Collaroy, is an array of five cameras, known as an Argus station, that takes time-averaged photos of the shoreline and surf zone. Tucked in among the cameras is a smoked-glass dome that looks like a space helmet: a lidar unit that uses a laser to measure wave swash and a cross-shore profile of beach elevation five times every second.

On our outing, Harley first drove us up Narrabeen Headland, to get an unobstructed southerly view of the bay. At the overlook was a stainless-steel post with a frame to hold a smartphone. This was the Narrabeen CoastSnap station.

In 2017, Harley, along with collaborators from the New South Wales State Government, launched the CoastSnap programme to collect crowd-sourced observations of beach dynamics (Harley et al., 2019). The process is simple: take a photo, post the image on social media with the station hashtag (#CoastSnapNarra, for example), and if you don’t post it right away, then write in the date and time of the image. With some clever analytical tricks, an algorithm finds the shoreline in your photo. Harley installed the first CoastSnap station at Manly Beach, above the Manly Surf Life Saving Club. There are now more than 35 CoastSnap stations in nine countries around the world.

Harley pointed out the various permanent features the algorithm uses to identify the shoreline position in every #CoastSnapNarra photo: an inlet hazard sign, the corners of prominent buildings in the foreground and distance. “We get about an image a day from people up here,” he said. Watching a sparse line-up of surfers work a peeling break at Narrabeen Inlet, we stood eating steak pies from The Upper Crust – like the surfers, another local institution.

Pies finished, we looped back down to the north end of the beach and assembled the GPS. The four of us would take turns walking the GPS receiver down the five main cross-shore transects still sampled at Narrabeen and Collaroy every month, and the three visitors would get our names added to the dataset’s long list of contributors.

Harley, Larré (holding GPS) and van Dam working through a beach profile. Credit: Eli Lazarus

In a reversal of cart and horse, I had written a scientific article about Narrabeen but never seen it. In fact, I was there in Sydney to visit people I had co-authored with but never met in person.

Earlier this year, Harley, Chris Blenkinsopp (of Bath University in the UK, and a former postdoc at WRL), Turner, and I published a paper in the EGU journal Earth Surface Dynamics about the information that shoreline records retain or destroy regarding the environmental conditions that shape them (Lazarus et al., 2019).

Extreme storm events, for example, can inscribe dramatic changes in the shape of a coastline. A detailed, high-frequency record of shoreline position presumably should reflect something about the magnitude of those events. But sedimentary systems can be very effective at obscuring or erasing their own histories, and not all evidence of conditions that impact a shoreline gets preserved. This phenomenon is known as ‘signal shredding’. The exceptional data catalogue for Narrabeen–Collaroy enabled us to pursue the first empirical test of signal shredding at a sandy beach, an idea I’d puzzled over since geomorphic signal-shredding was first described for other sediment-transport systems almost ten years ago (Jerolmack & Paola, 2010).

Among our survey crew, I asked to take Profile 4, near the middle of the embayment, because that was the record I had used the most when working through the signal-shredding analysis. To me, Profile 4 seemed to best capture, in a single line, the spatially variable character of the beach overall.

As we leapfrogged our way south, the beach profile became steeper and narrower. Harley mentioned an article that he had published with Turner and Short (Harley et al., 2015) that described, among other patterns at Narrabeen, a spatial pattern in the beach slope. If one end of the beach was steeply sloping toward the water, then the other end would be flat. The steep stretches of the beach tended to be narrow, and the flat stretches tended to be wide. Under certain wave conditions, the narrow, steep end of the would switch to being wide and flat, and vice versa – a pattern typical of embayed beaches called ‘rotation’.

As Harley described the slope pattern, the observation struck me as the kind that comes from investing time at a field site: the intuition internalised by surveying the beach over and over again in the seat of a quad-bike, from tipping sideways in the steeps and tracing the long meanders of the shoreline across the flats.

Standing astride the sharp break in beach slope at Collaroy, looking south toward Long Reef. Credit: Eli Lazarus

We finished the day with a walk around Long Reef, at Collaroy, looking back into the embayment we’d spent the afternoon traversing. Hang-gliders drifted in slow figure-eights above us. I was headed back to the UK the next day. There is more work to be done at Narrabeen, for sure, and we talked about what’s coming next: algorithms for predicting shoreline position (Davidson et al., 2017), fresh insights into beach recovery after major storms (Phillips et al., 2019), identifying shorelines from catalogues of satellite imagery (Vos et al., 2019). We talked about possible funding avenues to keep fuelling our collaboration.

The wind picked up, and the waves set to work rearranging the shoreline we had just measured.

Day’s end and hang-gliders at Long Reef, looking northwest toward Collaroy and Narrabeen. Credit: Eli Lazarus

By Eli Lazarus, University of Southampton, UK

Dr Eli Lazarus (@envidynxlab) is an Associate Professor in Geomorphology in the School of Geography & Environmental Science at the University of Southampton, UK.

 

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