Professor Dean Roemmich is one of the key figures behind the Argo Float Programme. Dean is a Physical Oceanographer and is co-chair of the Argo Steering team. He is based in San Diego at the Scripps Institution of Oceanography.

He was visiting Wellington recently, overseeing the preparation of 120 Argo Floats for deployment on Niwa's RV Kaharoa. I was fortunate to interview him (and give him a Cartesian "Argo Float" diver!)

How long have you been with the Argo Float Programme?

Since late 1997 when a number of us created Argo by writing a white paper (a plan) describing what the array would be.

How did ‘Argo’ come about?

We were aware that the technology of profiling floats had been developed in the early 1990s for the world ocean circulation experiment so people in a number of countries looked at that technology and said “really we should have a global array of these things. It’s feasible now to have global oceanography.” I think many people had the same idea.

Technology is changing all the time. What have you seen in the development of Argo?

There are 2 very exciting lines of development. One of them which we are already seeing is the two-way communication, replacing the old one-way communication. With the one-way communication, a float had to be on the sea surface for 10 hours and on the sea surface is where most bad things happen to them.

Now with two-way communication, it’s much faster because the float doesn’t have to keep repeating itself over and over again for 10 hours. Instead you know that there is always an Iridium satellite there. You establish contact between the float and satellite. Everything is done in 20 minutes and the float is down. That’s much safer for the float. It uses much less energy because lots of energy went into transmission. Also we can now send new orders down to the float. We can change the float’s mission parameters.

And you would do that if something obscure came up in the reading?

We would do that if say, the float drifted into a very interesting place that we wanted to go more often or maybe a float is in front of a tropical cyclone and you wanted to profile more quickly to a shallower depth because you wanted to observe something different. You can change the depth; you can change the cycle time. Everything can be altered.

That’s one very exciting line of development. The other one is about the depth they can go. These floats only go to about 2000m. That’s only about half of the ocean. We are now building prototype floats that will be capable of 6000m. The float will look completely different. A glass ball rather than an aluminium cylinder. We plan to start deploying prototypes from February next year. Maybe even from here.

That’s fantastic. Have we had any floats that have made it all around the world yet?

Not yet. One of these days. We have had quite a few that have gone more that halfway round.

What do you see for the future of these?

Well, what’s happened so far in this new generation of float is that they are smaller and I see that continuing. As you know, the buoyancy depends upon the size of the float. The smaller the float the less buoyancy change you need, so the less energy you need. I think we will continue to see the technology evolve, but there will also continue to be a real need to keep making these measurements so I see the programme continuing for another decade or more, but with the technology continuing to evolve. The basic measurements will remain temperature, salinity and pressure but we will see new sensors. The oxygen sensors will get better; the nitrogen sensors will get better. We’ll see pH; we’ll see biological properties also.

With the whole climate change, are we seeing what people have predicted with the evidence shown by the Argo profiles?

It’s an interesting question. I just published a paper a few months ago in “Nature Climate Change”. It compares Argo with data from the HMS Challenger expedition in the 1870s which was the first ever global ocean voyage. The Challenger made temperature profiles in 300 stages all over the world. We looked at the difference between Argo and Challenger and we saw warming of course. So recently some colleagues of mine have taken all those 300 Challenger stations/Argo stages and they looked at what the present generation of climate models (coupled-climate models used in the in IPCC report), what they say, and they agree very well actually. They show the same amount of warming as we observed. But, they are looking now at the period of the 1870s to the present and with the model, now you can remove the man-made part and you can say how much of this is due to anthropogenic (man-made) warming, CO2 emissions, and how much of it is natural and they found that it was virtually all man made, but it agreed extremely well with the temperature change.

This sort of finding would help with the whole Argo programme wouldn’t it?

It certainly does. It also shows, and I think we knew this from the first of those two papers that the warming in the ocean didn’t begin in the 1950s when we started making global measurements; it started much earlier than that.

What would you like to see with the education programme for Argo?

I’d like for the public, especially students, to be aware of what’s going on. People find it very exciting when they hear about it, but very few people know about it. That’s the challenge, to figure out how to make that connection so people actually know about it.

Thanks so much Dean. Just one last question. What’s your favourite ice-cream?

(laughs)

I’m pretty much a choc-o-holic. Chocolate icecream or chocolate chip icecream.