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We are in the State of Alaska and
we're out in the Eastern Aleutian Islands which are the large
islands of Eastern end of the Aleutian chains which forms
the The boundary between the North Pacific Ocean and the Bering Sea.
And what we're looking at out here is an inlet of the Bering Sea,
which is just to the north of us here.
We're in a sort of protected Bay, looking at a Mackinac Island and Hog Island,
which is where the archaeological sites are located that we've been studying.
The central research question driving this project is could there have been
sea ice on this landscape in this place 4000 to 2000 years ago and
we don't know the answer to that question.
See, ice entering these days would constitute a massive environmental change.
You've seen the boats going back and
forth, you see where people's homes are right on the shoreline.
If ice were suddenly to fill this day,
it would constitute a really dramatic environmental change.
One of the main ways that I can learn about whether there was ice
on this landscape and how people might have responded to that ice is to try to
reconstruct the environment.
And one of the great archives for paleoenvironmental
data that might actually lead me to this answer is a clamshell.
So that one probably is not >> Useful.
>> There's a whole bag of really, really good ones.
>> Yeah and here's a really nice one.
I mean the first part might be a little eroded.
But you're gonna cut it along the longest axis so that chunk doesn't matter but
yeah look at that.
The most abundant remains we find in the sites are fish and shellfish.
So we have literally found thousands of clams and they're beautifully preserved.
They're whole.
Those shells contain chemistry and chemical information that can tell us what
the environment looked like when people were living on that landscape.
>> We need to go through each bag because there are mixed species of shell and
find just the butter clams.
Then once we've isolated the butter clams we need to grade them in terms of how
well preserved they are.
>> Not clam.
>> Not clam
>> [LAUGH] >> These are good.
And then we can bag them all to send to Alabama and
put the rest back in the boxes to go back in the shelves.
So the reason that a clam works as a paleothermometer is because clams,
like other accretionary organisms, grow in rings and as it grows and
grows it's building its shell from the elements that exist in the ocean water and
those elements change according to the temperature of the water.
The shells are made of calcium carbonate CIC three, and to build that calcium
carbonate shell they have to uptake oxygen from the marine environment.
As temperatures cool they preferentially uptake more of the heavy isotope of
oxygen, oxygen 18.
As temperatures warm, they take up Less of the oxygen 18 and
from that chemical information you can
interpret what the temperature of the water was where this clam was living,
which is what you guys, of course, will be doing in the lab in Alabama.
>> So, we collected the clams at the Museum of the Aleutians and
sent them down to the University of Alambama,
along with a graduate student form Boston University and two undergraduates.
To work with Christine Bassett, who is a PhD student in geosciences.
>> I'm a paleoclimatologist.
And I work in very small subdiscipline of that called square chronology.
What we do is look at the skeletal growth of the hard parts of different organisms
like shells, corals, to see what they can tell us about the environment.
In the case of what Katherine is doing, it's on an archeological time scale and
all of the samples come from archeological shell.
We take just one of the valves from the clam and we section it on a table saw.
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Then we cut a three millimeter section of the shell that we can use either for
isotopic analysis or growth analysis.
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From there, what we do is submerge it in something called based solution.
That solution will bond to the organic material in this shell.
And it's gonna etch away the calcium carbonate.
And when you take it out, it'll be a nice bright blue and it'll
leave a really nice topography in staining all of our daily growth increments.
>> You can use the timing of that growth, the speed of that growth,
the rate of that growth to understand the environment in which that clam is growing.
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Now that the clam's been sectioned, we can drill into it.
So we use the micro-mill here.
Basically, we wanna drill these holes as close together as possible,
in order to get the best information that we can.
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so if we drill in a detailed way, in each of these growth rings, [SOUND]
We can put those samples into a mass spectrometer, pull out the oxygen, and use
that to estimate what the temperature of the water was when the clam was growing.
And so the clam shells will help us actually reconstruct the temperature
of the environment on an annual or seasonal basis.
When people were living in that place over thousands of years of time.
I find this just mind-blowing that this works,
that this little creature that lives for maybe up to 30
years can record such profound information about the ocean around it.
We are taking these samples in the context of an archeological question, a question
about human behavior and how humans responded to an environmental change.
But the record we're producing is being done in collaboration with geologists.
Who can produce a really robust understanding of past climate changes from
these small organisms and connect those patterns to our current understanding of
climate change today in 2017.
I think we can say with great confidence that we understand some of
these natural periods of change.
And what we're experiencing now is clearly not natural and is man made.
So it's pretty powerful.
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