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[Music]

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[Applause]

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all right thanks everyone I wasn't sure

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quite how many people to expect at the

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last talk of the conference but it looks

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like I don't get off easy with an empty

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room so let's go ahead so my talk is

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about a a couple of different microbial

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ecosystems I've been studying in sub

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glacial environments that we think are

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supported by Litha genic hydrogen I mean

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I wanted to you know I wasn't sure how

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much how short on time we'd be running

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by the end of the day so I want to make

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sure and get my thanks out here right

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away

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so dr. Eric Boyd is my PhD advisor and

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thanks to Mark who serves on my graduate

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committee melody and Rebecca are members

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of their respective labs who have each

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been helpful in the field work in the

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experimental work in the data analysis

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of these projects so one of the

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frameworks I like to approach this

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project through is you know an astro

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biological question of what makes a

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planet habitable and we can kind of go

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through a few first-order indicators of

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whether a planet may or may not be

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habitable so I've just taken these from

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the NASA NASA Astrobiology strategy

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document from 2015 and these are all you

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know these are important considerations

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to make in terms of narrowing our search

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for habitable worlds but in sort of a

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more through a more ecological lens we

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can think about more second-order

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constraints on microbial communities and

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the one I'd like to focus on today is

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that a microbial community needs a

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source of fixed carbon there has to be

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you know a base of the the trophic

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pyramid there has to be a population

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carrying out primary production and

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studying these environments on earth is

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sort of complicated by the fact that

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most primary production on our planet is

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carried out by photosynthesizers so we

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can put up you know this very simplified

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schematic equation of photosynthesis in

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which co2 and water through the energy

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supplied by photons are transformed into

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both reduced organic matter biomass and

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oxygen which is then you know the the

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oxygen is used to oxidize some of that

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photosynthate for

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energy and so the photosynthetic plants

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algae cyanobacteria are using energy

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from the Sun and co2 and water to get

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both reduced biomass and their carry out

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their energy metabolism if we look at

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something like an icy world habitat

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where we have no current indications of

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ongoing photosynthesis if we want to

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find microbial communities in this kind

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of an environment we're going to be

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having to look for those supported by

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geochemical sources of energy

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something like methanogenesis in which

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hydrogen and co2 may react to form again

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reduced carbon that can be assimilated

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into biomass and energy for metabolism

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so you know this this metabolism has

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been described as a free lunch that

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microbes are paid to eat as it produces

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both energy and organic matter so again

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just sort of the the complication here

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is that it's difficult to find

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environments on earth that are not

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supported on photosynthetically derived

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energy and organic matter and so kind of

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a refinement of our search for analog

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environments on our own planet would be

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to look for those that favor communities

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supported by chemo litho autotrophic

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primary production and so I've looked

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for these communities in sublation

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environments so beneath you know belief

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beneath hundreds of metres of ice you

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can reasonably assume that the influence

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of sunlight and photosynthesis have been

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excluded and depending on the bedrock

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beneath these glaciers there's not a

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whole lot of buried organic matter to

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support microbial communities either and

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we know that some of these communities

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are supported by chemo Luther autotrophs

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so Eric and Mark have done work over

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several years demonstrating

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methanogenesis in some sub glacial

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environments we can we can see through

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c14 tracer experiments that these

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organisms are indeed fixing co2 and we

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can show that comminution

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of sub glacial rock is enough to produce

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the hydrogen needed as a reductant to

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support these communities and so my

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thesis work is really focused on

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trying to identify whether differences

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in the underlying geology of a glacial

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system can influence the abundance and

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structure of the microbial communities

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in these systems and so I'm getting at

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that through the lens of hydrogen

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production again a key it's V key

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reductant for methanogenesis and heceta

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genesis in there fully autotrophic

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iterations and in a sub glacial

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environment or in water rock

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interactions there are a few different

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ways of generating hydrogen I think you

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know we've heard some at this conference

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about how some of these mechanisms are

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still under investigation

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but I just want to focus your attention

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on two key mechanisms one is silica

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shearing by glacial comminution can

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generate silica radicals which can you

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know split water and generate hydrogen

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radicals which will react with each

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other to produce hydrogen gas and there

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are also mechanisms by which ferrous

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iron can reduce water and Stevens and

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McKinley did some some work in the early

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late 90s early 2000s on you know low

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temperature water reduction by ferrous

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iron and so regardless of you know our

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understanding of you know the exact

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mechanisms by which these processes

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happen I think it's safe to build a

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hypothesis around the idea that in a

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system with higher silica content higher

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ferrous iron content with more of these

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potential mechanisms for hydrogen

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production we may see indeed higher

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levels of hydrogen dissolved in the sub

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glacial fluids and melt waters and we

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might expect that this environment would

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favor hydrogen atrophic primary

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production in the microbial communities

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associated with these environments so in

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order to try and demonstrate this

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phenomenon I'm looking at a pair of

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glaciers that differ in their bedrock

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geology so one is Robertson glacier here

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in the Canadian Rockies in the local

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bedrock is primarily carbonates there's

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some shales there's a decent amount of

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iron in the sediments beneath Robertson

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but low silica content and so this will

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be my model system of a sort of an

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environment

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low potential for hydrogen production

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and I'll be comparing these to a glacier

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in Iceland this is cot leocal which is

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in southern Iceland and overlays you

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know geologically speaking relatively

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fresh basalt so with a high silica

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content high in ferrous iron we might

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expect to see more hydrogen production

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after combination of this basaltic

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bedrock than we would at Robertson and

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so Everett shock was kind enough to

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provide some hydrogen data from the

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Robertson system and we can see there

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was about you know 40 to 50 nano molar

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hydrogen in the outflow waters at the

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time his group measured it here's our

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mobile geochemistry lab in Iceland and

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at Kotla local I was able to measure

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somewhere on the order of 400 to 500

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nanometer j'en in the outflow water so

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roughly one order of magnitude increase

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and this evidence was enough for me to

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continue with some cultivation work to

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look at whether these differences in

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available hydrogen between the two

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catchments actually translate to

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differential abilities of the community

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to utilize hydrogen as a reductant and

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to use hydrogen to fuel primary

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production and so in my activity assays

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I used a microcosm based approach I

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inoculated these with sediment slurry

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and a medium designed to mimic the

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composition of the pore water the

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outflow water at each of these glaciers

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I made them anoxic and gave them a 20

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percent co2 atmosphere to favor

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autotroph II added 500 ppm hydrogen and

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then as near as I could get to a 1

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millimolar concentration of various

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oxidants utilized in chemo litho

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autotrophic metabolisms and so the

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output from this experiment as I'm

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sampling the headspace and using a gas

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chromatograph to measure the total

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amount of hydrogen in these microcosms

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over time and you know I would expect to

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see in an abiotic control or a

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heat-killed control that the level of

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hydrogen stays relatively constant

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decreasing only to the extent that I'm

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pulling it out during sampling and that

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in a and inoculated experimental

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microcosm I should see maybe after a

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short lag period start to see hydrogen

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oxidation and so I have charts of this

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for each of the oxidants in each of the

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glaciers and those just get really

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complicated to look at so on the next

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slides the charts you're going to see

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are I've taken the maximum rate of

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hydrogen oxidation in terms of nano

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moles oxidize over the number of days in

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the measurement interval and I'll just

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jump to that so first here are the

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results for hydrogen there for Robertson

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excuse me so this is hydrogen oxidation

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and in across the x-axis I have my my

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control conditions my experimental

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conditions with the oxidant arranged by

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relative redox potential and then you

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can see on the y-axis the maximum rate

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of hydrogen oxidation observed in

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animals per day normalized to grams

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dry-weight sediment and so these are I

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don't see really any significant

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patterns in differences among the

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various supplied oxidants in this

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pattern or in the in this set of

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microcosms but what I did see is a major

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difference between the Robertsons

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sediments and the cotton local sediments

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so this suggests to me that indeed at

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this basalt based system where we

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observe higher hydrogen production we

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seem to see a community that is better

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adapted to take advantage of this geo

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genic energy source as a reductant

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fueling microbial metabolism and the

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story turns out to be pretty similar if

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I look at co2 fixation in these

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communities so again a microcosm based

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approach and to these microcosms i've

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added a small spike of 14c and again the

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same set of oxidants and I'll be looking

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in the next slide and again a maximum

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rate per day maximum rate in terms of

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nano moles fixed carbon per day and

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these again are a subset of the the

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rates that I observed over time as these

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experiments progressed and so if we look

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at the hydrogen or the co2 fixation

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results we can see with Robertson again

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predominantly low rates of co2 fixation

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with the notable exception of microcosms

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amended with nitrate as an ox and

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and I interestingly see the same pattern

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with the Katya locale loo yokel

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sediments excuse me again you can see if

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you look at on a pairwise basis at each

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of the oxidants that caught leocal

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consistently supports higher rates of

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co2 fixation and again we see this

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massive spike when nitrate is provided

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as the oxidant and so you know I'm still

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in the process of sorting of working

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through these results and in particular

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what it might mean that nitrate seems to

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support the highest rates of co2

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fixation and one hypothesis may be that

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these systems are nitrate nitrogen

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limited but in any case I think I hope

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I've been able to convince you that we

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may be able to correlate the abundance

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of minerals high in silicates and

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ferrous iron with the potential for an

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environment to produce hydrogen and we

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can use this potential for hydrogen

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production as a proxy for where we may

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find chemo litho autotrophic microbial

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populations supporting broader microbial

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communities so again I've shown that in

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a basalt hosted system we see

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populations of microbes that are better

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able to utilize hydrogen as a reductant

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and they're better able to couple that

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reductive or this hydrogen oxidizing

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metabolism with the ability to fix co2

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from the atmosphere thus serving as sort

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of a base of a trophic pyramid for a

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microbial ecosystem so in terms of

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future work on this project we're

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working with the skidmore lab on looking

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at the production rates of hydrogen from

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each of these sedimentary systems and I

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believe that paper has been accepted is

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that right mark it's so it's it's on its

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way

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you can talk to mark about that that

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project and then I'm in the process of

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working through the last set of

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experiments I have going with these

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sediments is most probable number array

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this is a monster set of inoculations in

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which I'm estimating the number of

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hydrogen atrophic and autotrophic cells

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in the sediments from each of these

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glaciers

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I'll be extracting DNA from these

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microcosms attempting to correlate it

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with the meta genome data we have from

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each of these sublation systems to learn

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more about the proportion of hydrogen

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atrophic in each of these microbial

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communities and you know try to get some

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more information about the structure and

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assembly of such communities so I'll

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leave you with with a question I'm

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looking for a name for my superhero

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alter ego this is the suit you can see

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here if you have any suggestions or

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other questions about the work I'd be

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happy to hear them except we have time

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for some questions already Eric I think

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there's one how do I saw a hand go up

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there I have a quick question for you

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Eric regarding your results that you saw

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the highest rates of carbon dioxide

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fixation in the nitrate reducing

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populations and do you think that's

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possible it's just sort of a

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thermodynamic ladder thing and nitrates

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a really good oxidant you know in turn

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relative to sulfate well I mean that

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that is one hypothesis that sort of

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immediately jumps out and I'm not sure

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how that relates to the rates we see for

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under oxide conditions in each of these

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in each of these sediment sets you know

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when idea is that we may be seeing

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evidence that these are ecosystems in

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which the microbes are adapted to

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anaerobic Kanak set conditions and

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perhaps nitrate is just serving as sort

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of sort of releasing nitrogen limitation

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in these systems it may be serving as

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primary oxidant for dissimilatory

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metabolism as well but yeah I'm not sure

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that I could say that it's just in

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relation to the redox ladder judging by

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the fact that the oxygen oxygen ik rates

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of hydrogen a trophy and carbon fixation

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that's always a possibility one thing I

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would like to do in terms of rerunning

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this co2 fixation experiment is to run

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some extra controls in which I don't

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provide any hydrogen because I think

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that may help tease apart some of the

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patterns I'm seeing especially with

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regard to early results of my most

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probable number experiments but yeah I

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would like to be able to at least

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confirm that this co2 fixation is or is

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not related to hydrogen a trophy