New paper

Andy Smedley | 23 March 2020

A little over two weeks ago the latest paper from the project was published. Given what’s happening in the world right now (it’s late March 2020), that seems a long time ago, but perhaps this short blogpost will provide some useful distraction whilst we all practise social distancing.

Occasionally meteorites will be found partly encased in the translucent ice, the ice underneath having melted and then refrozen [Credit: Katie Joy]

So our new study looks at how sunlight interacts with the blue ice where the vast majority of Antarctica’s meteorites are found. In the original paper that kicked off the project we used a simple mathematical model of how sunlight penetrates into the ice and how much is absorbed by the meteorite. How much sunlight is absorbed by a meteorite trapped in the ice determines how much it will heat up, and if it reaches the melting point of ice, how much the meteorite will then sink dow. In the original paper we used a fairly simple model of how sunlight is attenuated by blue ice and treated the system as one dimensional. In reality though it’s a 3D system and things are more complicated. One of the major ways in that it’s more complicated is that sunlight is made up of many different wavelengths (think the colours you see when it passes through a prism, or when a rainbow is visible, but extending beyond the range your eyes can see). Each of these wavelengths is affected by the ice properties slightly differently which means that the total attenuation is more subtle that we first assumed. When sunlight at infrared wavelengths hits the surface of the ice and passes into it, it’s rapidly absorbed by the ice. In contrast the part of sunlight corresponding to blue wavelengths is absorbed much less readily, and so is repeatedly scattered by the tiny bubbles within the ice. (These bubbles are actually tiny pockets of air trapped when snowflakes fell many thousands of years ago and their chemistry can help us understand how climate has changed on geological timescales.) As it so difficult for light at these blue wavelengths to be absorbed by the ice they continue to be scattered around inside the ice enhancing the amount of energy available to be absorbed by any dark meteorites present. As a result a meteorite sitting within the ice can act as a sink for nearby solar radiation, but, as well as absorbing more, because we now treat them 3-dimensionally, more energy is dissipated. To figure out how these different contributions balance out, we took the results of our sunlight modelling and added in the other things that might cause heating or cooling of the meteorite: the temperature of the air above the ice, the wind blowing over the surface, the motion of the ice, whether the meteorite gets warm enough to melt the ice and how far it then sinks and how these factors might vary over several years, plus the 3D nature of the problem.

It’s hard enough to find meteorites in Antarctica without them sinking into the ice. [Credit: Katie Joy]

All in, rather than iron meteorites being predicted to lie ~30 cm below the surface of the ice whilst their stony counterparts rise to the surface, this study suggests that the difference is much less, with iron meteorites being only 5-10 cm deeper than the stony ones. This isn’t a huge distance of course, and the blue ice is slightly translucent, but when you’re scanning from your skidoo for a speck of dark rock surrounded by the immensity of Antarctica, it’s enough to make spotting them virtually impossible. Interestingly though this new modelling shows the meteorite sinking mechanism is more nuanced than we first thought, with iron meteorites reaching the surface over the winter (when it is dark) before sinking into the ice early in the summer period after the sun rises. Though some questions remain, this seems more in line with what has been found in Antarctica as it gives the potential to find some iron meteorites if the conditions are right, and if the field expedition is during the early part of the summer.

If you fancy reading some of the technicalities of the paper, it can be found here.

Out and About

Katie Joy | 06 Jan 2019

We had a tent day yesterday sitting inside our tent waiting for the weather to improve. Everything looks a bit custard coloured in here after a while with the light coming through the orange canvas, so in the evening as the skies were clearing I walked around camp to see a stunning Sun halo made by the light reflecting through high altitude ice crystals with sun dogs glistening alongside.

We have been debating where the closest people are to us — Halley research station is about 687 km to the north, the South Pole research station is about 945 km to the south, and our ice drilling BAS colleagues are about 1060 km to the west. See photo of our little tent world in the middle of the ice, hopefully gives you a sense of the remoteness of our workplace.

2019-01-07 little tent world
Little tent world — no-one else for 687 km in any direction [Credit: K H Joy]

By morning the snow has blown through and sunny skies and light winds arrived this morning. Pilot Vicky, by now an honorary team member, came in with the red Twin Otter around lunchtime with the final skidoo and sledge load, and some bonus tasty fresh food treats from the chefs for our lunch (thanks guys!). Thanks to everyone back at Halley for all the field support — from skiway loading and transport, to copilots and skidoo wranglers, to comms and weather — it is all much appreciated.

Unloading a skidoo from the Twin Otter [Credit: K H Joy]

We managed to get out this afternoon to do some initial scouting around some of the ice fields close to us to see what the snow cover and ground is like on route. To get to new
areas we travel by linked travel — using a sledge and tow ropes linked up between the two skidoos. Tomorrow we will head out and do some searching further a field if the skies stay clear and see what the blue ice has to offer.

Linked travel: en-route to new areas [Credit: K H Joy]

PS to the other team members (now including Tom) who are in Punta: Hope you are enjoying yourselves in the sunshine and are preparing for the cold!

Taking the temperature of the ice [Credit: K H Joy]

Arrived!

Katie Joy | 02 Jan 2019

We made it to our first field site this afternoon. One flight out of three complete and Julie and I have set up camp. We are cosy in our tent and have had dinner (‘man food’ — rehydrated food which is actually much taster than anticipated). The rest of our gear will hopefully join us tomorrow including the skidoo and science equipment when Vicky and the twin otter plane return. We had a cloudy first part of the flight after a snowy night at Halley but the clouds cleared over the Shackleton mountains and, after a refuel stop, we did a fly-over of our potential next site to check out the blue ice and a possible traverse route.

We are camped on snow close to blue ice (where we hope the meteorites will be) and the ground is covered with amazing ice crystals like hoar frost that blow around in the 12 knot winds. They are sparkling in the sunshine like glitter. There is not a lot of topography on the horizon with no nunatuks (mountain tops protruding through the ice sheet) to be seen from our field site so it is somewhat stark not to have any scale reference.

Hopefully we will be out to work in the next couple of days.