Meet the… paleomagicians!

For our next “meet the scientists” we’re going to have a chat with our resident paleomagicians, Yoichi and Sam, who are going to explain why measuring the magnetic signature of ancient sediments is so important to an IODP cruise…


Good afternoon gentlemen. Can you please start by introducing yourselves to the good people of the internet…

ST: Hi, I’m Sam and I am a British rock magnetist (magician) working in IPGP (Insitut de Physique du Globe de Paris), France.

YU: I’m Yoichi Usui from Japan, and I work at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC).

Yoichi core pose   sam magentometer

[Yoichi taking pmag cubes from the core, and Sam getting ready to run the samples]

Thanks for joining us guys. So what’s your specialty on the JR and what does it involve?

ST: On this wonderfully-big boat, I make up one-half of the paleomagnetism team. In addition to the biostratigraphers, we use our magic to determine the ages of the recovered sediments. Here is a brief explanation of how. First I should mention that the Earth has a magnetic field, which protects us from solar wind. It is averaged as a dipole (i.e. a North and South pole) and through geologic time, these N-S poles have flipped, so the North becomes the South and so on (which is probably confusing for fish and birds). These ‘flips’ are known as polarity changes and have been reliably dated for many tens of millions of years. Therefore we look for changes in polarity within the sediments to give us age markers. This is possible since iron-bearing minerals, especially iron-oxides, are ubiquitous in natural sedimentary environments. They have the ability to record the state of the Earth’s magnetic field at their time of deposition (generally), so we can see whether we were in a normal polarity, or a reversed polarity

 YU: Paleomagnetism. As Sam says, it involves reading the geomagnetic field record naturally imprinted in sediments in the form of subtle alignment of nano-scale iron sand and alike (and packing cores after measurements; we are the last persons to process the cores in the lab). 


Ok, so you’re using the natural flips in the earth’s Magnetic field as a way of telling time. That’s very clever. So why exactly is this job so important to our expedition?

YU: Paleomagnetism can date the cores, by comparing the geomagnetic record with a standard pattern established elsewhere. The nice thing about the magnetic dating is that you can compare the results with almost everything everywhere; it would equally work on Hawaiian lavas or speleothems in caves.       

 ST: It is one of the most important jobs in any expedition. Sedimentary profiles wouldn’t be as useful are they are, and have been, without an estimate of their age and sedimentation rates as a result. Paleomagnetism is an independent method away from biostratigraphy, and in my (esteemed) opinion, provides more defined age determination than biostratigraphic events. This is because changes in the Earth’s magnetic field is a global phenomenon and therefore can be recorded anywhere, even with extremely low trace amounts of minerals.

Yoichi magentometer

[Yoichi working at (behind) the magnetometer – it wins the prize for the biggest piece of equipment we have in the JR lab]


Ah I see, so by measuring the paleomag signature in the rocks you can create a normal-reversed barcode pattern, which means we can convert depth in the core into time – always our ultimate goal! You and the biostratigraphers (like Clara and Oscar who I interviewed a few weeks ago) work closely together to produce the beautiful age models, which all the subsequent work is based on.

So that’s your job on the ship, but what is your regular area of research at home, and what are you working on at the moment?

YU: I’m trying to find the oldest geomagnetic record (so far I found one from 3.4 billion years ago). I’m also building an equipment to measure magnetic record from on-land rocks more accurately and rapidly, so that I can compare the results with sediments recovered by the JR or other ships.     

 ST: So I have just finished my PhD (woo!). I was using rock magnetism on loess-palaeosol deposits (terrestrial aeolian sedimentary deposits) to understand changes in the climate and environment during the last glacial period. I predominantly focused on 1) changes in the concentration, grain size and mineralogy of the mineral magnetic assemblage and 2) the anisotropy of magnetic susceptibility (magnetic fabrics), to further understand how changes in climate can shape magnetism.         

Congratulations on finding such an old record, Yoichi, and on becoming Dr Taylor, Sam! And what’s the scientific question you are both most hoping to answer with the new material from Exp. 353?

YU: Exactly when did the geomagnetic field reverse (we know it did reverse many times), and what happens at that times. 

 ST: The main aim of the expedition is to understand the physical mechanisms that drive changes in monsoonal precipitation, erosion, run-off and both atmospheric and ocean circulations. I wish to directly address these with an environmental magnetism study, while further improving the age models for the sediments in a region and time period questing for high quality data.

I’m sure the great material we’ve recovered will take you nearer to answering those questions over the next few years of work. So what’s the best part about being at sea on the JR? What has been the most fun (apart from hanging out with me which goes without saying)?

YU: Talking (both scientific and non-scientific) with people from various countries.            

ST: Food, food, oh glorious food.

 (They feed us constantly on the boat with cakes and cookies and fried food – if you have a big appetite, the JR is the place for you…).

IODP Expedition 353 Indian Monsoon

Ok, food and talking. Good choices. Now what is the worst part about being at sea and what  do you miss most from home?

ST: As Juliet (Education Outreach officer) would say every time she comes past the lab during a video outreach  session “So who has had problems with seasickness?”. I had one bad day with seasickness, which I blame myself 100% for because I bought the wrong tablets. Fortunately, there is a very good doctor on board! In terms of missing things from home, not being with family over Christmas was a little sad. However, we all had a lot of fun on Xmas day with caroling, lots of entertainment and of course, too much food.

YU: Fresh vegetables.

 I hear you Yoichi – the first thing I’m going to do when I get to Singapore is have a salad. Most probably with a generously proportioned beer.

Ok gentlemen, thanks very much for taking the time to inform us about the wonderful world of paleomagnetism. You’ll never be as cool as the sedimentologists, but you give it a good try! 🙂

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