GeoTalk: Dr Stephanie Henson

GeoTalk, featuring short interviews with geoscientists about their research, continues this month with a Q&A with Dr Stephanie Henson (University of Southampton) who tells us about her work on marine ecosystems, and gives great advice to young scientists. If you’d like to suggest a scientist for an interview, please contact Bárbara Ferreira.

Dr Stephanie Henson

First, could you introduce yourself and let us know a bit about your current research topic(s)?

I started out as an undergraduate in physics at the University of Leicester before moving into oceanography with a Masters degree at the University of Southampton. After a couple of years as a science administrator, I moved back into academia with a PhD in oceanography, also at the University of Southampton. I did postdocs in America at the University of Maine and Princeton University, and now I’m a biogeochemical oceanographer at the National Oceanography Centre in Southampton, UK. I’m interested in how the physical environment affects phytoplankton and carbon uptake. Phytoplankton are tiny plants that live in the ocean and although they only make up 1% of Earths biomass, they absorb almost half of atmospheric CO2 and produce about half of the oxygen we breathe. They are also the base of the marine food web, and support fish, whales, etc. Most phytoplankton can’t swim and so are at the mercy of ocean mixing and currents which determine how much light and nutrients they receive. I’m interested in understanding how variability (on seasonal, inter annual and longer time scales) in phytoplankton and carbon uptake arises, and use a combination of satellite, ship, and model data to achieve this.

Earlier this year, you received an EGU Arne Richter Award for Outstanding Young Scientists for your ‘fundamental contribution to the study of marine ecosystems’. Could you summarise the research you have done in this area?

I’ve spent much of my career so far investigating how phytoplankton are affected by changes in the ocean environment, for example wind patterns, ocean mixing, eddies, etc. One of the clearest examples of these interactions is the annual ‘spring bloom’. Just as on land spring heralds a sudden greening of the trees and plants, in the ocean the phytoplankton bloom when conditions are right; an event which is very important for providing food to fish and other marine animals, but also for absorbing CO2 from the atmosphere. The year to year variability in physical conditions leads to variability in the timing, size and distribution of the phytoplankton bloom, which I’ve studied mainly with satellite ocean colour data. Bringing in situ data and modelling into the mix, I’ve looked at how longer term variability, such as changes in the North Atlantic Oscillation might affect phytoplankton.

A second strand of my research has been assessing the strength of the ‘biological carbon pump’ – a term that refers to the transfer of carbon from the upper ocean to the deep ocean where it is locked away out of further contact with the atmosphere for thousands of years. The pump is a key part of the global carbon cycle, but my recent work has suggested it may not be as large as once thought. This is worrying because it means our knowledge of a major planetary carbon flux is incomplete. I’ve also studied how the pump strength changes spatially in the ocean, which gives us some ideas for what might control its variability.

Among other topics, you are interested in “trends in ocean primary productivity“. Could you explain to us what ocean productivity is and how it can vary (due to, e.g., climate change)?

Phytoplankton use light and CO2 to photosynthesise and produce oxygen – this process is called primary production. Anything that alters the amount of light or nutrients that phytoplankton receive can alter primary production. Because of the need for light, phytoplankton live near the surface of the ocean. They get their nutrients from the water itself, but most of the ocean’s nutrients are in the deep, dark water. The amount of light and nutrients a particular patch of the ocean gets depends mostly on the physics happening in the ocean and atmosphere, which changes the amount of mixing in the upper ocean. Too little mixing and there won’t be a good supply of nutrients from the deep waters; too much mixing and the phytoplankton will be mixed into deep waters and won’t receive enough light. Climate change will lead to increased ocean temperatures, reducing the amount of mixing in many regions. This is predicted to result in a general decrease in ocean primary production, which might lead to a positive feedback loop: decrease primary production, decrease CO2 uptake, warmer planet, less ocean mixing, decrease primary production, and so on.

What are your future research plans?

I’m working in several areas connected to understanding variability in phytoplankton, for example combining data from new technologies to understand the spring bloom. We’ve recently deployed ocean gliders in the Northeast Atlantic, which can sample from the surface to about 1000m depth for months at a time, to investigate the physical processes that prompt the start of the spring bloom. By combining satellite data, which gives us information on the surface patterns of phytoplankton, with the glider data, which tells us about the vertical distribution, we hope to gain a whole new perspective on this long-standing question. I’m also investigating methods to detect signatures of global warming in time series of marine ecosystems. We have over 15 years of satellite data on phytoplankton, but it’s not long enough yet to easily distinguish a trend from the natural variability, so we’re trying out sophisticated statistical analyses, but also investigating some of the long in situ time series as well.

You have an impressive CV! At a young age, you are not only an active and successful researcher, but you are also leading a research group, teaching, and supervising PhD students. What advice would you give to young students looking to pursue an academic career in the geosciences?

The first thing I’ll say is going to seem obvious, but the second part of it maybe not so much. First, work hard. But not too hard! Personally, I avoid work on evenings or weekends unless it’s an emergency. I find that to be productive and creative, I need to step away from my computer regularly. I suspect the same is true for most people, so although it’s tempting to put in crazy hours when things get tough, try going for a long walk and having an early night instead – you might work more efficiently tomorrow!

I’d also advise students not to be afraid to challenge the status quo. It’s easy to accept the existing assumptions and paradigms, but I say ‘question everything’. Much of the time the existing paradigm will be correct (and in questioning it you will have learnt a lot), but sometimes you may spot a gap in our knowledge or reasoning. If you do, don’t be afraid to explore it – it might be the route to a new insight in your field!

Finally, I can’t emphasise enough the importance of supportive mentors to help you along the way. If your tutor or supervisor is a good mentor, cultivate the relationship and maintain it even if you move to another university. You may also meet academics in your field at conferences or meetings that you develop a rapport with. Don’t be afraid to pick their brains about career choices, or discuss ideas with them – most academics will be flattered to be sought out for advice.

Bárbara Ferreira was the Media and Communications Manager of the European Geosciences Union from 2011 to 2019. Bárbara has also worked as a science writer specialising in astrophysics and space sciences, producing articles for the European Space Agency and others on a freelance basis. She has a PhD in astrophysics from the University of Cambridge.

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