Hi, my name is Sasha Turchyn, and I'm in
the Department of Earth Sciences, at the
University of Cambridge.
And today, I wanted to talk to you about
the carbon cycle.
Now, you've probably learned about the
carbon cycle in school, or you might have heard
about it in the media;
it basically refers to the movement of
carbon all around
our planet. We think of carbon as
being hosted in several reservoirs,
some examples of reservoirs that have
carbon in them are: the atmosphere
and the ocean, biology, soils. And we're
particularly interested in the carbon
that's in the atmosphere, in the form of
carbon dioxide or methane.
That's because both carbon dioxide
and methane are powerful greenhouse
gases and they determine how warm
our planet is. In addition to thinking
about how much carbon is in each of
these reservoirs, we often think about
the processes - or the rates of these
processes that take carbon from one
reservoir to another.
For example, photosynthesis and
respiration. But really you could draw
arrows all over this diagram, talking
about the rates and magnitudes at which
carbon is moved
from one box to another.
There's a reservoir missing from this
slide: that
is the rest of the planet. And carbon on
the rest of the planet is in the form of
a rock or a mineral -
it's in the magma that is coming out of
volcanoes, it's down deep in the mantle
in the centre of the Earth.
And it turns out there's five orders of
magnitude more carbon
in the rest of the planet than there is
at the surface.
What I'm particularly interested in
is what brings
carbon from the rest of the planet to
the surface,
and what takes carbon that's at the
surface and returns it into a rock or a
mineral, or back into the mantle.
And so the research question, that my
group has been thinking about for the
last 15 years, or so
is how does carbon move between the
surface and subsurface of the planet?
And more specifically, the question that
we've been thinking about for the last
five to seven years
is how do bacteria and other small
organisms single cell organisms
process carbon and move carbon? And what
role do they play in the carbon cycle?
This is particularly interesting because
bacteria, when they
process carbon, can produce methane and
sometimes they can produce carbon
minerals such as calcium carbonate -
the limescale that you find on the
bottom
of your kettle. So my general field of
research is in
Geo (and "geo" refers to Earth)-microbiology
and that's because I study microbes, I
study bacteria and archaea, and what
they are doing.
My secondary scientific hat
is in the field of bio, for biological,
geo, for Earth, and chemistry because,
at heart, I'm a chemist and so I'm
interested in the chemical signals that
bacteria and archaea are leaving behind,
so that I can understand the role that
they play in the carbon cycle.
So how do I do this research? Well we
often go into the field to collect
samples to see what bacteria in the
environment are doing.
Last summer, I had the opportunity to go
to Lake Baikal, in Siberia,
onto a research cruise, and we were out
there for two weeks.
And on this cruise we would do some
sampling of the water column,
where we send bottles down to different
depths and trap water.
We did some sampling of the mud at
the bottom of the lake -
and you can see here this is a coring
device, that we would use to collect
samples from the bottom of the lake.
We would bring the cores to the
surface: you can cut them open, and
take a look at what you find. And you can
describe
the mud, you can take samples, so you can
characterize the biology.
You can also do sampling right there, we
had a chemistry lab on board, so we could
do chemical sampling of the fluids in
the muds to try and see if we could see
the chemical changes that are driven by
the bacteria living in the mud.
And sometimes, when we were very lucky, we
would find
these cores that would come up with
these white rocks
in them: they look like white rocks,
but they're actually ice
and they are ice that is formed with
methane in the middle.
So the bacteria have made methane
but, rather than the methane as a gas
escaping to the surface,
it's formed an ice crystal and that's a
very interesting question: why do
bacteria sometimes make methane that
gets trapped as ice?
And under what conditions might that ice
melt and release the methane back to the
surface?
What's really neat about having methane
and ice is that you can light it on fire!
I don't know if you can see the
flame coming off the cold piece of ice
in my hand there, but hopefully you
can see it in this video,
where i'm holding a piece of ice that is
on fire.
We also bring samples back to the lab,
where we can put
bits of bacteria and mud into vials. We
sometimes
amend those vials (that means we add
something or take something away)
to see if we can change what the bacteria
are doing,
and sometimes we'll look at the output
under a scanning electron microscope -
here what we have is a bunch of
bacterial cells that have become
entombed in minerals that they've made,
almost accidentally. Their metabolism
generated the chemicals that allowed
them to mineralize
their cells, and that makes these sorts of
mineralized globules.
And these are all carbon-bearing
minerals, that have tied carbon up in a
mineral form.
So I started this talk with a picture of
the Earth,
and we're interested in understanding
how carbon moves in and around the Earth.
What i'd like to leave you with is
the idea that, by understanding the role
that microbes play
in mineralizing or releasing carbon; they
are the engines that are driving the
carbon cycle.
Thank you very much for your time!
