With a Little Help from the Elephant Seals

A problem which has plagued oceanography since the very beginning is a lack of observations. We envy atmospheric scientists with their surface stations and satellite data that monitor virtually the entire atmosphere in real time. Until very recently, all that oceanographers had to work with were measurements taken by ships. This data was very sparse in space and time, and was biased towards certain ship tracks and seasons.

A lack of observations makes life difficult for ocean modellers, because there is very little to compare the simulations to. You can’t have confidence in a model if you have no way of knowing how well it’s performing, and you can’t make many improvements to a model without an understanding of its shortcomings.

Our knowledge of the ocean took a giant leap forward in 2000, when a program called Argo began. “Argo floats” are smallish instruments floating around in the ocean that control their own buoyancy, rising and sinking between the surface and about 2000 m depth. They use a CTD sensor to measure Conductivity (from which you can easily calculate salinity), Temperature, and Depth. Every 10 days they surface and send these measurements to a satellite. Argo floats are battery-powered and last for about 4 years before losing power. After this point they are sacrificed to the ocean, because collecting them would be too expensive.

This is what an Argo float looks like while it’s being deployed:

With at least 27 countries helping with deployment, the number of active Argo floats is steadily rising. At the time of this writing, there were 3748 in operation, with good coverage everywhere except in the polar oceans:

The result of this program is a massive amount of high-quality, high-resolution data for temperature and salinity in the surface and intermediate ocean. A resource like this is invaluable for oceanographers, analogous to the global network of weather stations used by atmospheric scientists. It allows us to better understand the current state of the ocean, to monitor trends in temperature and salinity as climate change continues, and to assess the skill of ocean models.

But it’s still not good enough. There are two major shortcomings to Argo floats. First, they can’t withstand the extreme pressure in the deep ocean, so they don’t sink below about 2000 m depth. Since the average depth of the world’s oceans is around 4000 m, the Argo program is only sampling the upper half. Fortunately, a new program called Deep Argo has developed floats which can withstand pressures down to 6000 m depth, covering all but the deepest ocean trenches. Last June, two prototypes were successfully deployed off the coast of New Zealand, and the data collected so far is looking good. If all future Argo floats were of the Deep Argo variety, in five or ten years we would know as much about the deep ocean’s temperature and salinity structure as we currently know about the surface. To oceanographers, particularly those studying bottom water formation and transport, there is almost nothing more exciting than this prospect.

The other major problem with Argo floats is that they can’t handle sea ice. Even if they manage to get underneath the ice by drifting in sideways, the next time they rise to the surface they will bash into the underside of the ice, get stuck, and stay there until their battery dies. This is a major problem for scientists like me who study the Southern Ocean (surrounding Antarctica), which is largely covered with sea ice for much of the year. This ocean will be incredibly important for sea level rise, because the easiest way to destabilise the Antarctic Ice Sheet is to warm up the ocean and melt the ice shelves (the edges of the ice sheet which extend over the ocean) from below. But we can’t monitor this process using Argo data, because there is a big gap in observations over the region. There’s always the manual option – sending in scientists to take measurements – but this is very expensive, and nobody wants to go there in the winter.

Instead, oceanographers have recently teamed up with biologists to try another method of data collection, which is just really excellent:

They are turning seals into Argo floats that can navigate sea ice.

Southern elephant seals swim incredible distances in the Southern Ocean, and often dive as far as 2000 m below the surface. Scientists are utilising the seals’ natural talents to fill in the gaps in the Argo network, so far with great success. Each seal is tranquilized while a miniature CTD is glued to the fur on its head, after which it is released back into the wild. As the seal swims around, the sensors take measurements and communicate with satellites just like regular Argo floats. The next time the seal sheds its coat (once per year), the CTD falls off and the seal gets on with its life, probably wondering what that whole thing was about.

This project is relatively new and it will be a few years before it’s possible to identify trends in the data. It’s also not clear whether or not the seals tend to swim right underneath the ice shelves, where observations would be most useful. But if this dataset gains popularity among oceanographers, and seals become officially integrated into the Argo network…

…then we will be the coolest scientists of all.

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Rewinding the Clock

I don’t really care about the panda bears. But that’s not saying this problem [climate change] isn’t serious. This is a people problem, this is a billion dead people problem. This is a national security problem. This is rewinding the clock 300 years to a time we don’t want to go back to.

– Nick Wood (spoken at a presentation I attended, and possibly slightly paraphrased as I scrambled to write it down; his profile is here)

My Cartoon Supervisors

My supervisors are so distinguished that they now exist in cartoon form! If that’s not the mark of a successful science communicator, I’m not sure what is.

Here is Katrin:

And here is Matt:

A former supervisor of mine also got a cartoon:

There are 97 cartoons like this over at Skeptical Science, a site which is quickly becoming a force of nature. This campaign reached millions of people through Twitter alone, and was even retweeted by President Obama.

A New Chapter

It has been a very busy few months. Here are some of the things I have done since I last wrote:

  • Moved out of our apartment in Canada
  • Spent three weeks in Ireland with my partner’s family – this was great fun and featured lots of music, tide pools, castles, and sheep
  • Went back to Canada for six days
  • Mastered the art of packing checked luggage and carry-on bags so they are juuust under the weight limit
  • Said a lot of tearful goodbyes
  • Flew to Australia!
  • Discovered Sydney was 11°C and raining
  • Immediately regretted leaving all our warm sweaters behind (“It’s spring in Australia,” we said. “We won’t need these for months yet,” we said)
  • Saw all three animals I had missed the most – bats, lorikeets, and scientists – in the very first day
  • Officially enrolled as a PhD student at UNSW
  • Stumbled into the Sydney real estate market, where rent prices are more than double what we are used to, and only the wealthiest people can afford to buy property
  • Managed to find a great little apartment for rent within our budget
  • Bought out most of IKEA
  • Moved into said apartment (we’re getting good at this moving thing)
  • Helped to finish up 3 papers from the project Katrin, Tim, and I did last year, and 1 paper from the project Steve and I did 3 years ago
  • Read at least a dozen papers on interactions between Antarctic ice shelves and the Southern Ocean – my PhD project will be somewhere in this field
  • Gone out for climate beers (regular beers consumed by climate scientists) and discussed whether the Canadian or the Australian political system is more fundamentally broken
  • Swam in the ocean three times, and discovered that if you put on goggles and look underneath the water you can see FISH swimming around beneath you

Things are finally calming down now, and I should have time to write more frequently. Now that my head is not so full of flight schedules and rental agreements and shopping lists, it has a lot more space for climate science, and for topics to write about here.

I am so, so happy to be back at the CCRC. It is such a friendly, supportive, and enriching place to do research. While I miss my family and the Canadian wildlife and Canadian autumn (definitely not Canadian winter), this is the best time in my life to travel and explore the planet which I spend so much time studying, and hopefully, helping.

Explaining the Seasons on ‘Game of Thrones’

If you haven’t yet watched the television series Game of Thrones or read George R. R. Martin’s A Song of Ice and Fire books on which the show is based, I would urge you to get started (unless you are a small child, in which case I would urge you to wait a few years). The show and the books are both absolute masterpieces (although, as I alluded, definitely not for kids). I’m not usually a big fan of high fantasy, but the character and plot development of this series really pulled me in.

One of the most interesting parts of the series – maybe just for me – is the way the seasons work in Westeros and Essos, the continents explored in Game of Thrones. Winter and summer occur randomly, and can last anywhere from a couple of years to more than a decade. (Here a “year” is presumably defined by a complete rotation of the planet around the Sun, which can be discerned by the stars, rather than by one full cycle of the seasons.)

So what causes these random, multiyear seasons? Many people, George R. R. Martin included, brush off the causes as magical rather than scientific. To those people I say: you have no sense of fun.

After several lunchtime conversations with my friends from UNSW and U of T (few things are more fun than letting a group of climate scientists loose on a question like this), I think I’ve found a mechanism to explain the seasons. My hypothesis is simple, has been known to work on Earth, and satisfies all the criteria I can remember (I only read the books once and I didn’t take notes). I think that “winters” in Westeros are actually miniature ice ages, caused by the same orbital mechanisms which govern ice ages on Earth.

Glacial Cycles on Earth

First let’s look at how ice ages – the cold phases of glacial cycles – work on Earth. At their most basic level, glacial cycles are caused by gravity: the gravity of other planets in the solar system, which influence Earth’s orbit around the Sun. Three main orbital cycles, known as Milankovitch cycles, result:

  1. A 100,000 year cycle in eccentricity: how elliptical (as opposed to circular) Earth’s path around the Sun is.
  2. A 41,000 year cycle in obliquity: the degree of Earth’s axial tilt.
  3. A 26,000 year cycle in precession: what time of year the North Pole is pointing towards the Sun.

These three cycles combine to impact the timing and severity of the seasons in each hemisphere. The way they combine is not simple: the superposition of three sinusoidal functions with different periods is generally a mess, and often one cycle will cancel out the effects of another. However, sometimes the three cycles combine to make the Northern Hemisphere winter relatively warm, and the Northern Hemisphere summer relatively cool.

These conditions are ideal for glacier growth in the Northern Hemisphere. A warmer winter, as long as it’s still below freezing, will often actually cause more snow to fall. A cool summer will prevent that snow from entirely melting. And as soon as you’ve got snow that sticks around for the entire year, a glacier can begin to form.

Then the ice-albedo feedback kicks in. Snow and ice reflect more sunlight than bare ground, meaning less solar radiation is absorbed by the surface. This makes the Earth’s average temperature go down, so even less of the glacier will melt each summer. Now the glacier is larger and can reflect even more sunlight. This positive feedback loop, or “vicious cycle”, is incredibly powerful. Combined with carbon cycle feedbacks, it caused glaciers several kilometres thick to spread over most of North America and Eurasia during the last ice age.

The conditions are reversed in the Southern Hemisphere: relatively cold winters and hot summers, which cause glaciers to recede. However, at this stage in Earth’s history, most of the continents are concentrated in the Northern Hemisphere. The south is mostly ocean, where there are no glaciers to recede. For this reason, the Northern Hemisphere is the one which controls Earth’s glacial cycles.

These ice ages don’t last forever, because sooner or later the Milankovitch cycles will combine in the opposite way: the Northern Hemisphere will have cold winters and hot summers, and its glaciers will start to recede. The ice-albedo feedback will be reversed: less snow and ice means more sunlight is absorbed, which makes the planet warmer, which means there is less snow and ice, and so on.

Glacial Cycles in Westeros?

I propose that Westeros (or rather, the unnamed planet which contains Westeros and Essos and any other undiscovered continents in Game of Thrones; let’s call it Westeros-world) experiences glacial cycles just like Earth, but the periods of the underlying Milankovitch cycles are much shorter – on the order of years to decades. This might imply the presence of very large planets close by, or a high number of planets in the solar system, or even multiple other solar systems which are close enough to exert significant gravitational attraction. As far as I know, all of these ideas are plausible, but I encourage any astronomers in the audience to chime in.

Given the climates of various regions in Game of Thrones, it’s clear that they all exist in the Northern Hemisphere: the further north you go, the colder it gets. The southernmost boundary of the known world is probably somewhere around the equator, because it never starts getting cold again as you travel south. Beyond that, the planet is unexplored, and it’s plausible that the Southern Hemisphere is mainly ocean. The concentration of continents in one hemisphere would allow Milankovitch cycles to induce glacial cycles in Westeros-world.

The glacial periods (“winter”) and interglacials (“summer”) would vary in length – again, on the scale of years to decades – and would appear random: the superposition of three different sine functions has an erratic pattern of peaks and troughs when you zoom in. Of course, the pattern of season lengths would eventually repeat itself, with a period equal to the least common multiple of the three Milankovitch cycle periods. But this least common multiple could be so large – centuries or even millennia – that the seasons would appear random on a human timescale. It’s not hard to believe that the people of Westeros, even the highly educated maesters, would fail to recognize a pattern which took hundreds or thousands of years to repeat.

Of course, within each glacial cycle there would be multiple smaller seasons as the planet revolved around the Sun – the way that regular seasons work on Earth. However, if the axial tilt of Westeros-world was sufficiently small, these regular seasons could be overwhelmed by the glacial cycles to the point where nobody would notice them.

There could be other hypotheses involving fluctuations in solar intensity, frequent volcanoes shooting sulfate aerosols into the stratosphere, or rapid carbon cycle feedbacks. But I think this one is the most plausible, because it’s known to happen on Earth (albeit on a much longer timescale). Can you find any holes? Please go nuts in the comments.

Two Great TED Talks

Both are about climate modelling, and both are definitely worth 10-20 minutes of your time.

The first is from Gavin Schmidt, NASA climate modeller and RealClimate author extraordinaire:

The second is from Steve Easterbrook, my current supervisor at the University of Toronto (this one is actually TEDxUofT, which is independent from TED):

What I am doing with my life

After a long hiatus – much longer than I like to think about or admit to – I am finally back. I just finished the last semester of my undergraduate degree, which was by far the busiest few months I’ve ever experienced.

This was largely due to my honours thesis, on which I spent probably three times more effort than was warranted. I built a (not very good, but still interesting) model of ocean circulation and implemented it in Python. It turns out that (surprise, surprise) it’s really hard to get a numerical solution to the Navier-Stokes equations to converge. I now have an enormous amount of respect for ocean models like MOM, POP, and NEMO, which are extremely realistic as well as extremely stable. I also feel like I know the physics governing ocean circulation inside out, which will definitely be useful going forward.

Convocation is not until early June, so I am spending the month of May back in Toronto working with Steve Easterbrook. We are finally finishing up our project on the software architecture of climate models, and writing it up into a paper which we hope to submit early this summer. It’s great to be back in Toronto, and to have a chance to revisit all of the interesting places I found the first time around.

In August I will be returning to Australia to begin a PhD in Climate Science at the University of New South Wales, with Katrin Meissner and Matthew England as my supervisors. I am so, so excited about this. It was a big decision to make but ultimately I’m confident it was the right one, and I can’t wait to see what adventures Australia will bring.