GeoLog

GeoTalk: Talking about ‘ocean burps’ with James Rae

GeoTalk: Talking about ‘ocean burps’ with James Rae

Trying to understand the reasons behind the global warming of our climate is a never ending quest for scientists across the geosciences. Scientists often rely on deciphering past change to help us understand, and perhaps predict, what might happen in the future. Many will be familiar with the common saying ‘the past is the key to the future’. This is exactly what James Rae, a research fellow at the Earth & Environmental Sciences Department at the Universty of St. Andrews and this year’s recipient of the Biogeosciences Division Outstanding Young Scientists Award, has been focusing his efforts on. James’ research interest lies in understanding past climate change and he was recognised by the Biogeosciences Division after the publication of his research into ocean ‘burps’ – he and his colleagues found that changes in ocean circulation in the North Pacific caused a massive ‘burp’ of CO2 to be released from the deep ocean into the atmosphere, helping to warm the planet sufficiently to trigger the end of the ice age.

Before we get stuck into the details of your work, could you introduce yourself and tell us a little more about yourself and your career?

My name’s James Rae and I’m a geoscientist at the University of St Andrews. I actually grew up just down the road – in Edinburgh – but only just moved back to Scotland last year, after studies in Oxford, Bristol, and California. The locals tell me that the transition from LA to St Andrews shouldn’t be too tough – apparently St Andrews is “one of the sunniest places in the whole of Scotland”!

I got into geosciences through a love of the outdoors and outdoor sports – mountain biking, surfing, snowboarding, climbing – and though most of my work is now in a super clean lab, I still try to get out in the Scottish Highlands whenever possible.

My career to date has focussed on using geochemistry to reconstruct past environmental change. This means I make measurements of the chemistry of things like shells, fossils, rocks, and ice, which often reflect aspects of the environment they formed in. So by making a series of these measurements on fossil shells back through time we can see how the environment changed in the past. My specialty is using boron in tiny fossil shells, called foraminifera, to reconstruct past CO2 change.

So, ocean ‘burps’? During EGU 2015, you received the Biogeosciences Division Outstanding Young Scientists Award for your study of this unusual phenomenon. Can you tell us more about those?

One of the most interesting things about the ice ages of the last few million years is that they seem to be punctuated with really dramatic rapid climate change. The most recent examples of this are at the end of the last ice age – between about 20 and 10 thousand years ago – where we see intervals of rapid CO2 rise recorded in ice cores. The only place where you can quickly get enough carbon to drive these CO2 changes is the deep ocean. During ice ages we think CO2 gets hidden away beneath the waves, at water depths of 2000 – 5000m, and because the Pacific is so big it’s likely that a lot of this CO2 is stored down there. Other scientists had suggested that this CO2 remerged at the end of the last ice age in the ocean round Antarctica. However my research shows that it could also “burp” out in the North Pacific.

Schematic of how James use boron isotope measurements in foraminifera to reconstruct pH and CO2. Credit: James Rae

Schematic of how James use boron isotope measurements in foraminifera to reconstruct pH and CO2. Credit: James Rae

And how exactly did the release of CO2 in these ‘burps’ affect the climate of the ice age?

Our Pacific “burp” happens right at the beginning of the end of the last ice age – it coincides with the first CO2 rise that heralds the start of the deglaciation. It’s possible that the warming associated with the CO2 “burp” helped push the earth out of it’s ice age, though we need to do more work to test this. But even aside from the CO2, the change in circulation that drove this event had a big influence on local climate. Although most of the Northern Hemisphere is really cold at this time the North Pacific is actually quite warm, which I think is a result of this unusual circulation state.

So, the Northern Hemisphere was very cold at this time; can you describe a little more what the Earth might have looked at during this time and how the local climate of the North Pacific might have been different?

At the end of the last ice age massive ice sheets still covered much of North America and Northern Europe. Over St Andrews the ice was around a kilometre thick. Then, at the beginning of the last deglaciation, in an interval called Heinrich Stadial 1, the ice sheets round the North Atlantic start collapsing. This flooded the North Atlantic Ocean with fresh water and reduced the Atlantic overturning circulation that currently provides heat to this region. As a result much of the Northern Hemisphere got colder. However the climate in the North Pacific does something very different. Likely in response to the big cooling in the North Atlantic, there was a large change in the position of major rain belts, like the Westerly storm track and East Asian Monsoon, and we think this acted to make the North Pacific more salty. This led to a more vigorous overturning circulation in the Pacific, a regional warming, and a burp of CO2 release from the deep sea.

What is the next step, if you like, in order to better understand ocean ‘burps’?

At the moment our key evidence for the North Pacific burp comes from a single sediment core. To test the idea we really need to make more measurements from other cores in this region. Our main evidence for ocean CO2 change also currently comes from records from the deep ocean. One of my PhD students is currently making new records to test how much CO2 made it up from the deep to the surface ocean, and from there to the atmosphere. Finally, with collaborators in Switzerland and the US we’re also testing the physical driving mechanisms of this circulation change using state of the art climate models.

(L) An ocean cruise on which the sediment cores used in the study are collected. (R) Benthic foraminifera - James uses these to make measurements of the chemistry of these to reconstruct past climate change. Credit: James Rae

(L) An ocean cruise on which the sediment cores used in the study are collected. (R) Benthic foraminifera – James uses these to make measurements of the chemistry of these to reconstruct past climate change. Credit: James Rae

You’ve enjoyed success as a researcher, not least your 2015 EGU Award. As an early career researcher, do you have any words of advice for masters and PhD students who are hoping to pursue a career as a scientist in the Earth sciences?

Do what you really enjoy. This feeds in to everything else you do; it means you’ll work hard and carefully in lab, find the reading interesting, and be able to present your work effectively to your colleagues. We do science because we love it, so it’s really important to find topics within your field that you love working on. I think it’s also helpful to find skills to be a specialist in and be known for, but then to try to apply these broadly to big picture questions in geosciences.

Laura Roberts-Artal
Laura Roberts Artal is the Marketing Manager at PDS Ava (part of PDS Group) and Associate Director of Communications for Geology for Global Development. Laura was the Communications Officer at the European Geosciences Union from the summer of 2014 to the end of 2017. Laura is a geologist by training and holds a PhD in palaeomagnetism from the University of Liverpool. She tweets at @LauRob85.

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