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Midges as environmental indicators -

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Steve Brooks: A midge...a lot of people think of midges as the things that bite you, especially in
the northern hemisphere, but the midges I'm interested in are non-biting midges. There's actually
far more species of them than the biting sort. They're extremely abundant in all sorts of
freshwater habitats but in particular in lakes, and one thing that's really good about them from my
point of view is that they're extremely good environmental indicators. We find the remains of the
larvae in lake sediments...we can take cores out of lakes, slice these cores up into fine intervals
and then look at changes in the abundance and in the diversity of the midges through time, and that
can tell us a lot about how the environment has changed in the past.

Robyn Williams: And how far have you been going back in time?

Steve Brooks: Most of the work is going back to the last ice age, which is about 15,000 years ago,
but quite recently I've been looking at sediments from hundreds of thousands of years ago from a
site in the east of England which is connected with a site where they've been looking for human
remains. In fact they think that at that period there weren't any humans in Britain at that time.
So we can go back a long time.

Robyn Williams: And so how do you see something different about the midges that can tell you
something about what the weather was like?

Steve Brooks: What we've found, by looking at the distribution of midges in northern Europe today
we know that some species are associated with cold environments and some species are associated
with warm environments. In fact what we've been able to do is to work out the optimum temperature
for each midge species. Then when you go back in time looking at these sediments that have
accumulated over thousands of years, you can look at a particular assemblage of midges from the
past and work out what the temperature would have been to give you that assemblage of midges.

We can actually test our model by seeing how well it works in the present day. We can look at a
present day midge assemblage, use our model to construct a temperature, and we know that the error
in the model is around about one degree centigrade. If we slice the sediments at two-millimetre
intervals, which in a lot of lakes is around about every ten years, in theory we can work out what
the temperature was every ten years for the last 15,000 years with an accuracy of about one degree
centigrade. So we can get a really good idea of what the temperature was like in the past and also
how fast the temperature has changed in the past as well.

Robyn Williams: Isn't that exciting! They are so helpful midges, aren't they.

Steve Brooks: They are, yes. Really my first love is dragonflies and I like spending days going out
looking at dragonflies, but as much as I like midges, they're not really the most exciting things.
But from the point of view of finding out about past climate change they're actually very
interesting. We can look at other things as well. We can look at changes in trophic levels of
lakes. In other words, how much they've received nutrients, for example, over the last, say, 50, 60
years. So we can see how lakes have been polluted by nutrients, we can look at how lakes have been
affected by acid rain as well. I've done work as well looking at the impacts of smelters in Russia,
for example. We looked at a copper smelter and, again, the midges changed in characteristic ways
which helped us to understand basically what the impact of the smelter was on the lakes surrounding
it.

Robyn Williams: How clever. Tell me, did you get a picture of the temperature change that was in
any way surprising as a result of this work?

Steve Brooks: It's surprising in the sense of how fast the temperature can change. We did have an
idea about that already because there are similar techniques used with beetles. Beetles can tell
you the same sort of information. The trouble with beetles is that you need several kilograms of
sediment to get enough beetles out of it to give you a temperature reconstruction. With midges we
can use less than a gram of sediment and get hundreds of midge heads out of a gram of sediment. So
what it means is we can look at very much more fine intervals.

So while we knew from the beetles that, for example, temperatures had changed five or six
degrees...the last time the Gulf Stream switched off, about 11,000 or 12,000 years ago, we knew
from the beetles that the temperature had changed by about five degrees but it wasn't clear how
fast it had changed, and we know from the midges that it happened within ten years or so, a massive
change in temperatures in a very fast time.

Robyn Williams: It went down, got colder, I suppose.

Steve Brooks: It got colder, yes. Basically what happened was that the last ice age was finishing,
temperatures were increasing and that meant the that ice sheets were melting, but the effects of
that was that there's lots of fresh water going into the northern Atlantic Ocean and it was
diluting the ocean current which drives the Gulf Stream, and the effect of that was to switch the
Gulf Stream off. So although climate was warming, the Gulf Stream switched off because of the
melt-waters and that plunged north-west Europe back into an ice age which lasted about 1,000 years,
even though global temperatures were actually on an upward trend.

Robyn Williams: Yes, it's such a paradox, isn't it. And of course we're thinking about the Gulf
Stream right now, aren't we.

Steve Brooks: Yes, exactly. There is evidence already that the Gulf Stream has slowed down by about
30%, so while it's not enough to cause cooling temperatures and we haven't detected any response
from midges, for example, it's conceivable (especially if the ice cap on Greenland melts) that
again it could switch the Gulf Stream off. The last time that happened, as I say, it took 1,000
years for it to come back online again. Actually, when it did come back, of course the temperatures
went up very quickly again. Within, again, about ten years the temperatures shot right up again.

Robyn Williams: It's amazing how quickly these things can turn around. I suppose we've got plenty
of midges in Australia to do the same sort of work.

Steve Brooks: Yes, and actually somebody has done work...very few studies in Australia but there
has been some work done....again, with interesting results. In fact we don't really know as much
about climate dynamics in the past from the southern hemisphere as we do about climate dynamics in
the northern hemisphere, and so there's a lot of debate really about how influential southern
weather systems are on global temperatures or even global weather systems. Is it the southern
weather systems that are driving the north, or are they synchronised, are there leads and lags
between them? And there's still a lot of work to be done on that.

I'm actually working in southern South America looking at climate changes. In fact, I'm looking at
this same period where the last time the Gulf Stream switched off, just to see if there were any
measurable effects in South America at the same time or whether perhaps there were any leads or
lags between that period. So that's work that is still going on. But yes, there's plenty of
opportunity in Australia for anybody who's interesting in getting into that. As far as I know
there's only been about one study so far using midges.