Paleoceanography proxies

Tina van de Flierdt from the Department of Earth Science and Engineering at Imperial College London is an international leader in the use of geochemical proxies – particularly neodymium (Nd) – for reconstructing past ocean circulation, water masses and weathering. But her childhood and early interests pointed in a different direction.

In the lab with graduate students
Tina (right) in the lab with graduate students.

Tina grew up on a dairy farm in rural western Germany, raised by parents who were largely tied to the land but entirely supportive of her outside interests and desire to attend summer camp away from home. By her late teens, Tina knew she had a keen interest in geology, but didn’t realize that it existed as a field. It took the combination of an inspirational teacher and a sharp career counselor to set her down the path that’s led her to where she is today.

Initially, however, Tina wanted to be a hard rock geochemist, or to study volcanoes and mantle processes — passions that drew her to work in Namibia. Then, following an off-hand comment by a friend, Tina sent her CV to Alex Halliday, at the time working at ETH Zurich. Although she had no particular interest in paleoceanography, the moment she entered the lab, Tina thought “…well, screw it, I’ll do paleoceanography”. That’s all it often takes to switch gears entirely.

Tina then dove into early work on the use of Nd to trace water masses, and was a first-hand participant in the seemingly inevitable progression of a new proxy from optimism to pessimism and later reconciliation. Along the way, Tina helped to lead the GEOTRACES program, a massive international effort to disentangle the many influences on geochemical tracers. As I keep hearing on the podcast, it was a case of being in the right place at the right time, particularly if that place was Lamont.

Tina is particularly interested in the marine-terminating sector of the East Antarctic Ice Sheet during past warm periods. With her team, Tina is already producing evidence to suggest that it may be as sensitive to warming as the West Antarctic Ice Sheet. If so, the implications for sea level rise are obviously startling, and Tina is now working to move from qualitative statements to a quantitative reconstruction of past mass loss.

For a long time, the modeling community was well ahead in trying to generate these sorts of estimates, but as Tina tells it, the geochemists are rapidly catching up and the field is now in a fantastic-sounding state of collaboration and mutual stimulation of ideas.

We talk through several career topics, too: watching out for open-ended technical analysis in your early days; the unexpected rewards of teaching; the merits and problems of the UK academic assessment process; and management of peer review, particularly now that Tina is an editor at Geochimica et Cosmochimica Acta.

Climate change: it’s more than physics

Reto Knutti. Photo credit: Valérie Chételat, used by permission of ETH Zurich.

Reto Knutti and I are both interested in cake. Reto, as an analogy for the problems society faces when trying to divide up the allowable carbon emissions among historically greedy and newly desirous consumers. Me, because I love cake (ok, it’s also a great analogy).

Who wouldn't want to have as much of this as possible?
A delicious cake I made. Who wouldn’t want to have as much of this as possible? There’s caramel inside too!

Reto is a stellar climate physicist, working on many angles of climate system, including climate sensitivity, ocean circulation, aerosols, radiative forcing, changes in extremes, and allowable carbon emissions (most recently at Nature, he co-authored a paper on how regional extremes scale with global mean temperature — figure below).

Figure 3 from "Allowable CO2 emissions based on regional and impact-related climate targets" Nature doi:10.1038/nature16542.
Figure 3 from “Allowable CO2 emissions based on regional and impact-related climate targets” Nature doi:10.1038/nature16542.

Hard core IPCC Working Group I stuff, you could say.

But Reto is also interested in climate and society interactions. He’s done dozens of outreach activities, has clear ideas about how to engage with non-scientists, and thinks deeply about what models are and how to use them. So I decided to steer the conversation more towards social/policy/economics angles … fields in which neither one of us has formal training, making it all the more fun.

Reto has certainly tried hard to build scientific bridges among fields. In his experience, the theoretical and practical challenges in working across disciplines are enormous and the immediate benefits can be scant. For Reto, working with economists and social scientists: produced “…some of the hardest papers to write, ever”. And some of this work is cited hardly or not at all. If you don’t start, though, you’ll never get anywhere, and Reto doesn’t seem to regret any of the considerable effort he’s put into “non-core” activities.

In this vein, I posed a series of quasi-unanswerable questions (paraphrased):

Q: How do you get society to stop eating so much cake? A: Perhaps by massive regulation or massively reduced use, but neither seems likely. Massive investment in research and technology might be a better way forward.

Q: What’s the best way to engage with a range of civic and financial institutions on climate change? A: Keep facts and values separate: “rather than telling people what they need to do, you tell them what the facts are, what the options are, and you let them basically think on their own about what they could do or what they need to do”. Shared values definitely helps.

Q: Given that the EU and the US are at approximately similar points on the Kuznets curve, why do they have such different attitudes towards climate? A: The EU tends to think more as a society and less as an individual, and the US has fundamentally different geographical constraints and faith in technology to solve problems.

Q: How do you decide whether or not there are fundamental limitations to model projections … or put another way, is there a question for which the answer is so uncertain that modelers shouldn’t even provide an answer (inspired by Lenny Smith)? A: That’s a tough one, and actively debated in the modeling community. At the least, you can evaluate against the paleo record, check for consistency across models, and compare to modern observations. But the potential still exists that models could be missing some sort of critical physics or constraints. The potential for this kind of “miss” is probably highest for the things that are really relevant for society, like extremes and abrupt change.

Reto kindly indulged my open-ended questions about these and many other thorny issues. We did, of course, eventually get around to talking about some actual physics of the climate system!

Valérie Masson-Delmotte and the jigsaw puzzle of climate science

For Valérie Masson-Delmotte, climate science is like a jigsaw puzzle. Unlike a house of cards, where the removal of one element causes the whole thing to crash down, the central picture of a puzzle is still apparent when pieces — maybe even many pieces — are missing.

MASSON-DELMOTTE Valérie
Valérie Masson-Delmotte. Rights-free image by Pierre Maraval for the “1000 Researchers project”.

Valérie works, at least in part, to fill in the missing pieces, using tools like ice cores, climate models, and statistics. I guess you could say that Valérie is an ice core scientist, but that’s like saying that Eric Ripert knows how to cook fish. Yes he does, and he’s great at it, but that kind of misses the bigger picture.

In fact I would have a hard time trying to pin down what Valérie does, because the range is so broad, spanning monsoon modeling, polar climate variability, interpretation of δ18O, age models, volcanic impacts on climate … I suppose it’s simplest to say that Valérie is trying to understand past climate variability and the underlying processes, on an astonishing variety of fronts. A great example of how Valérie and her colleagues are bringing together multiple archives and techniques is a recent Nature paper on the reconstruction of the North Atlantic Oscillation.

Figure 2 from "A model-tested North Atlantic Oscillation reconstruction for the past millennium" by Ortega et al. doi:10.1038/nature14518.
Figure 2 from “A model-tested North Atlantic Oscillation reconstruction for the past millennium” by Ortega et al. doi:10.1038/nature14518.

That’s not all, though. Valérie is the co-chair of Working Group I for the sixth IPCC assessment report, a children’s book author, and the mother of two teenage daughters.

It seems like nearly everyone gets into science by some roundabout way. In Valerie’s case, her early interest in archaeology morphed into engineering. But then, in the process of deciding whether or not to stay in science, a chance encounter with a popular science article on the Vostok ice core led to her cold-calling the French scientists who were involved in the project, and soon, the day after finishing her PhD on monsoon modeling, a postdoc at the new LSCE with the great Jean Jouzel.

The timing was perfect and, for a brief time, Valérie and her colleagues could pursue any sort of curiosity-driven science they wanted. Those days are long gone, but Valérie is still a passionate supporter of long-term, curiosity-driven science.

One theme that keeps emerging in my interviews with climate scientists is the way in which larger cultural practices inform how science gets done. For Valérie, French culture has some specific practices, particularly around raising questions. As she says, “We are not taught to ask questions … questions are supposed to reflect how smart you are … but not acknowledge your ignorance”. Yet it doesn’t seem that Valérie has any issues asking tough, reasonable questions, like when she takes me to task for not accepting important methodological advances for publication in Nature (at least in climate).

Our interview, recorded at the end of the March 2016 IPICS meeting in Hobart, Tasmania, was a great chance to hit some of the nitty-gritty of ice core science. We hash through CO2 offsets, age model synchronization with speleothems and tephra, integration of ice core records with ocean and non-polar terrestrial records, and the hunt for the oldest ice.

The many careers of Piers Sellers

I first heard of Piers Sellers some time in the mid-1990s, on a trip to the southern BOREAS field site when I was in my master’s program at the University of Montana. The talk was something on the order of “… have you heard? Piers is entering the astronaut program!” which, at the time, came as a complete non-sequitur to me. Why would someone at the peak of an influential scientific career at NASA choose to walk away?

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Lixin Wu and the rising tide of Chinese oceanography

I met Lixin Wu when I was at the Ocean University of China in Qingdao for a writing workshop (now called Nature Masterclasses). Several things impressed me about Lixin right away. First, he’s a lot of fun to be around and equally at ease in formal situations and banquets. Then, he’s clearly an inspiration to his staff and colleagues. Finally, he has big visions for his own science, the OUC, and Chinese marine science in general.

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Three decades of ice core science with Dorthe Dahl-Jensen

Dorthe Dahl-Jensen is one of the leaders of the second generation of Danish ice core scientists, following on from pioneers like Willy Dansgaard and Sigfus Johnsen. She’s began publishing in Nature and Science since 1993, and now has 16 papers between the two. Her career spans technical details, modeling, age models, abrupt change, isotopic interpretation … nearly any topic you can imagine about the Greenland ice cores.

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Into the deep ocean with Lorraine Lisiecki

Lorraine Lisiecki is in the business of understanding past variations in ocean circulation. In particular, she uses mathematical approaches to interpret observed variations in δ18O and δ13C on times scales of thousands to millions of years.

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Yusuke Yokoyama narrowly misses career in baseball, settles for stellar career in science

Nearly everyone I’ve interviewed so far has a healthy dose of “what if” in their background. But maybe no one more so than Yusuke Yokoyama, a star paleoclimatologist – geochemist – engineer – inventor at the University of Tokyo.

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Amy Clement questions the core ideas of climate dynamics

Essentially from the start of her career, Amy Clement has been interested in the big ideas in atmospheric dynamics. But she’s also continually raised questions and proposed her own sometimes controversial ideas.

Amy Clement
Credit: UM Rosenstiel School of Marine and Atmospheric Science

El Niño is fundamentally linked to atmosphere-ocean interactions? Maybe not. The Atlantic Meridional Overturning Circulation drives the Atlantic Multidecadal Oscillation? Again, maybe not. Continue reading →

Stefan Kröpelin and 45 years of exploration and science in the eastern Sahara

Interesting stories and insights on life come tumbling out of Stefan Kröpelin — one of the foremost scientists working in the eastern Sahara — like snowflakes in a blizzard. Science is at the forefront of our conversation, but his worldview is literary: “It was never my intention to make, out of 100 books, the 101st.” Always, Stefan looks for the empty space and fresh opportunity, on the map and in science.

Stefan Kropelin at Lake Bokou, Chad. Credit: Stefan Kropelin.
Stefan at Lake Bokou — part of the Lakes of Ounianga UNESCO World Heritage Site, northern Chad. Credit: Stefan Kröpelin.

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