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So, today we're going to talk about,
we've talked about primary

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productivity on a global scale last
time.  And today,

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we're going to talk about what
regulates that productivity.

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In other words, last time we just
talked about on average the amount

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of carbon and biomass that was
distributed among the ecosystems

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of the globe.
And we talked about deficiencies of

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transfer of that biomass through
food webs, etc.

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By the way, the one universal thing
that everybody seems to like are the

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DVDs at the end of the class,
which is good.  Unfortunately,

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in today's class we are not going to
have one.  So you have something to

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look forward to on Wednesday.
I'll show you one at the end that

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is really one of the cooler ones of
the collection.

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It has nothing to do with the
lecture but I'm going to

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show it to you anyway.
OK, so today we are going to talk

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about what regulates the
productivity.  We've talked about

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these complex systems in ecology,
and the feedback mechanisms.  So, in

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the context of productivity we're
going to talk about the factors,

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the abiotic factors, to the
non-living parts of the Earth,

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that regulate this productivity and
how the productivity feeds back on

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those.  And then Wednesday,
we're going to put it all together

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in an analysis of global
biogeochemical cycles,

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how the elements in the globe cycle,
and how that's mediated by organisms.

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And then, that will be the end of
the segment.  And when I come back,

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we're going to move on to population
and community ecology,

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which will feel like a totally
different subject to you.

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So, we'll talk more about organisms.
And some of you said it was so

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interesting to see math last time in
the last lecture even if they were

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just efficiencies.
Well, when you get to population

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ecology, you're going to have real
math and you'll actually have

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differential equations.
So, if you like that you have

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something to look forward to.
If you don't like it, well, it's

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not too bad.  OK,
so today the lecture will be in two

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halves.  We'll talk about
terrestrial productivity,

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and then aquatic productivity and
what regulates it.

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And, can you see in the back or do
I need to turn,

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I'm going to have to turn the lights
down, never mind.

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So, because we have some colored
images, so let's start with

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terrestrial productivity.
And look at this map, oops,

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wrong ones.  I think that might be
enough to see it,

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which is a satellite image.
You've seen several of these so far.

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So just showing the gradients of
productivity on a global scale,

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where we're just looking at the land
now.

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Where it's green,
you have high levels of productivity.

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These are grams carbon per meter
squared per year.

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Yellow is intermediate,
and red is very low levels of

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productivity.  So,
what determines this distribution of

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productivity in terrestrial
ecosystems?  Well,

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got any ideas?  This is not hard.

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What's a key factor in regulating
plant growth on land?

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Light, absolutely.  That's a given.
But looking at this map, what's

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probably more important?
Water, exactly.

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If we plot on a global scale,
if we go around to all these

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ecosystems, and we look at the
average annual rainfall and we plot

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it against net primary productivity,
you all know what NPP is right, net

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primary productivity,
you get a graph that look something

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like this.  Each one of these dots
would be an ecosystem.

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And this one is millimeters rain
per year.

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So, despite the Sahara Desert,
and this might be a tropical rain

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forest.  And they scatter,
but there's some sort of general

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relationship like that,
increasing NPP with increasing

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rainfall.  Well,
what else is probably important?

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What else is different between the
Sahara Desert and the northern

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US?  Temperature.
Exactly, which is not a good example

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for comparison.
Let's take tropical rain forests

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and the northern US.
How's that?  But you get something

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like this.  In other words,
it doesn't always map directly onto

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temperature alone.
But on average, you find that

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places with higher temperature have
higher productivity if there's

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adequate water.
So, does a relationship,

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there's an interaction between the
water and the temperature.

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So, those are the key factors for
terrestrial ecosystems.

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Now, what we have, so there's light,
nutrients, I mean light,

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rain, and temperature, rainfall.
What about nutrients?

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Anybody who's had plants and their
room, or nurtured our garden knows

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that nutrients are very important.
You have to fertilize in order to

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get the most growth.
So, how does that work?

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Well, now we are going to do an
analysis of a terrestrial ecosystem.

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We're going to use a tree.  Some
ecosystems you have,

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that's a rock in case you didn't
recognize it.

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And we have soil.
These are components.

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And, we've talked about this over,
and over, and over now.

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Photosynthesis is the key,
taking up CO2, evolving oxygen,

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we are going to call this
biosynthesis.

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That's the mass from gas.
So, that's CO2 plus, and now we're

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going to add something.
And these are not balanced chemical

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reactions, OK?
These are just to give you an idea

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of what's going on.
So, CO2  plus, there's all the

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elements required for life,
OK?  In other words, for a plant to

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grow, it doesn't only
need CO2 and water.

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It needs all of these elements
required for life.

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And they are converted to organic
forms of those elements.

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And then oxygen is evolved.
So, we are in a general sense,

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just modifying the equation for
photosynthesis to include all of the

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elements that are required for life.
So that's the biosynthesis.

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And then, the tree,
these are leaves in case you didn't

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recognize them,
that are falling to the soil.

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And the leaves fall down to the
soil and they become,

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what?  What's that organic manner?
You learn it last time.  It's the

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whale falling to the bottom of the
ocean, and if that was a carcass,

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the general term for dead, organic
matter is called detritus.

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And there is a detritivore food web,
remember?  And we had some

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discussion with students after class
whether we were detritivores,

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because in a sense we are because we
eat dead meat,

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right?  We don't eat live meat.
It doesn't matter.  You don't have

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to know that.  Forget that.
But it's interesting to think about.

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So, the leaves fall down to the
soil.  They are acted upon by the

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heterotrophic bacteria,
the bacteria that use organic carbon.

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And, what happens is that those
bacteria and fungi,

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and worms, and everything that chews
on organic matter are responsible

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for regenerating these elements in
the soil.  So,

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we are going to call that
regeneration.  And that's basically,

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simply the back reaction of this, OK?
So, you are starting

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with organic carbon.
And, organic carbon,

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organic PNS, and it's converting it
back to the inorganic forms so that

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they're available for the tree to
take up again.

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So, this is the cycle of
biosynthesis regeneration,

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and then take it up again.  Some of
the feedback I got on the lectures

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when people said that they found it
interesting to think about how

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everything in nature is
recycled and used.

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Now, in some ecosystems,
there's another form of available

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nutrients: calcium here,
you have cations, potassium from

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rocks, magnesium.
All of these are also in this

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equation.  When I go dot,
dot, dot, dot, it's every element

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that's required for life.
And in some ecosystems,

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the [disillusion?] of these elements
from rocks is an important renewal

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route for nutrients in the ecosystem,
OK?  So these are the two,

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basically in terrestrial ecosystems,
there is the rock source, and

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there's the regeneration source.
And it turns out that different

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terrestrial ecosystems have
different relative dependence on

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these two sources.
And this is an interesting phenomena.

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So, tropical rain forests,
like in the Amazon, these are the

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forests that we're concerned about
losing for many reasons.

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And these have, essentially,
no number one up here.

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Tropical rain forests have
essentially no renewal nutrients

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from bedrock.  And temperate forests,
however, have a combination of one

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and two.  They can have renewal.
The bedrock is exposed, and the

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water cycle helps dissolve the rock,
and renews the nutrients to the

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system.
So, if we look at the soil to

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biomass ratio of phosphorus and
nitrogen in the temperate forests

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versus the tropical, we see
something like this.

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In the tropical rain forests,
all of the nutrients in the system

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are basically tied up in the biomass.
And it's highly dependent,

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then, on this regeneration cycle.
The trees fall down, it's

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regenerated, it's taken up right
away from the soil whereas in the

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temperate system,
you see the opposite where there's a

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much higher proportion of nutrients
in the soil relative to

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the tropical system.
And what that means is that if you

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cut down a tropical rain forest,
which they're doing, converting to

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farmland, you will only get a few
years of productivity out of that

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farmland because once you shut down
the forests and haul away the trees,

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you've hauled away most of the
nutrients in that ecosystem that are

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available to fuel productivity.
And they can't be renewed from

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bedrock because they don't have
bedrock there.

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So, that's one of the tragedies of
cutting down these forests when they

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probably would have more economic
value by harvesting some of the

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natural products from
the forests.

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OK, so when we get to aquatic
productivity, we are going to see

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that we have these same biosynthesis
and regeneration processes.

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So, that's what we're going to move
to now.  And let's look at the

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distribution of aquatic productivity.
That's too much.

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A while.  Can you see that in the
back OK, the colors?

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All right.  So, now we're just
looking at the ocean's ecosystem.

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And areas that are blue and green
are less productive than the areas

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that are red and yellow in the
system.  So you can see all of the

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coastal regions; we have coastal
upwelling that we're going to talk

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about a lot with nutrients fueling
that, that is very important.

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And on the whole north Atlantic here
we'll talk about that.

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But before we talk about what
regulates aquatic productivity,

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now I am going to turn the lights
out, I thought I'd give you a tour.

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Since you all know trees look like
but you don't know what primary

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producers in the ocean ecosystems
look like, I'm going to give you a

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quick tour through the phytoplankton,
which as you know, are my

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favorite organisms.
So, the aquatic productivity is

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dominated by these microscopic
plants.  There are over 20,

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00 species, but we really have no
idea how many there are.

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Wherever there's water, they exist.
They range from 0.5 to 1,000 µ in

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diameter.  And as I told you in the
first lecture,

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there's as much genetic information
and a liter of seawater that

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contains these primary producers and
all the bacteria but they live with

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than there is in the human genome.
So here's some of my favorites.

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These are marine diatoms.  This is
a silicon shell.

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This is a single cell.
It's about 30 µ in diameter.

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And this is made out of amorphous
silicon.  It's essentially opal.

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And here's another one.  They come
in different shapes and sizes.

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They're just really incredibly
beautiful.  And people are just

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starting to study what mechanisms
are responsible for laying down

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these exquisite architectures.
Here's another one.

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To me this always remind me of the
Coliseum for some reason.

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These are pillbox shaped cells.
And they have two halves like that.

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And when they grow, when they
divide, one half lays down another

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half inside of it.
Now, what's going to happen

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ultimately if these are rigid?
They get smaller.

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One lineage gets smaller,
and smaller, and smaller.  Well,

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both of them get smaller, and
smaller.  And this group of

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organisms has this really neat
system where when it gets really

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tiny, they differentiate into egg
and sperm.  They made,

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and that they make a giant cell
again.  And they start the whole

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thing.  It's cool.
Just to show you some of the things

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people have studied,
people have wondered why have they

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evolved this very heavy armor?
And of course,

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the first thing you think about is
resistance to predation.

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But there was never any evidence
for that.  And so,

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I just found this recent study in
nature that shows where they

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actually measured.
I thought MIT students look like

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this because they actually measure
the force that it takes to crush one

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of these cells.
Here's the study.

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There is a diatom [thrustule?
and they're putting a measured

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force on it to see what
would crush it.

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And they were able to show that the
amount of force that it takes is

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enough to have a selective advantage
against the crunching parts of the

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zooplankton that eat them.
I also want to point out, this is

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from the website of Dr.
Angela Belcher, who is a professor

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here at MIT and material sciences.
And she is studying diatoms.

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Here's a diatom.
She's studying them as a material,

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this amorphous silicon, looking at
the way it's laid down.

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And she's also studying
coccolithophores,

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which is another group of my
favorite organisms.

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They have these calcium carbonate
plates.  Again,

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this is a single cell.
But it's cell wall is made up of

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00:18:47,000 --> 00:18:51,000
calcium carbonate plates.
And they come in all different

221
00:18:51,000 --> 00:18:54,000
shapes and sizes.
Here's a really weird one with

222
00:18:54,000 --> 00:18:57,000
these huge, they're called
coccoliths.  And these cells,

223
00:18:57,000 --> 00:19:00,000
this is a satellite image of
reflection, of light.

224
00:19:00,000 --> 00:19:04,000
In these cells, the calcium
carbonate, reflects light.

225
00:19:04,000 --> 00:19:08,000
And this is a coccolithophore bloom
somewhere I think in the Bering Sea.

226
00:19:08,000 --> 00:19:12,000
And we can measure these, but we
have no idea what causes a

227
00:19:12,000 --> 00:19:16,000
particular species to bloom at a
particular point in time.

228
00:19:16,000 --> 00:19:20,000
It's one of the challenges of
oceanography.  Here's another group

229
00:19:20,000 --> 00:19:25,000
of organisms.  The cyanobacteria:
we've talked about them a little bit.

230
00:19:25,000 --> 00:19:29,000
These are prokaryotic cells that
can fix nitrogen.

231
00:19:29,000 --> 00:19:33,000
They're one of the few groups of
microbes that can take nitrogen gas

232
00:19:33,000 --> 00:19:37,000
from the atmosphere and convert it
to ammonia, which draws

233
00:19:37,000 --> 00:19:42,000
it in to the food web.
So you can actually see a bloom here.

234
00:19:42,000 --> 00:19:46,000
That one's called trichodesmium.
It grows out in the open Atlantic

235
00:19:46,000 --> 00:19:50,000
and Pacific.  Here's a bloom of
trichodesmium sucking nitrogen into

236
00:19:50,000 --> 00:19:54,000
the ecosystem,
converting it into ammonia,

237
00:19:54,000 --> 00:19:58,000
making it available to the other
organisms.  Here's the organism we

238
00:19:58,000 --> 00:20:02,000
work on, unfortunately very boring
looking, not as exciting looking at

239
00:20:02,000 --> 00:20:06,000
the other ones.
And now, this is just under a light

240
00:20:06,000 --> 00:20:11,000
microscope.  These are less than a
micron in diameter.

241
00:20:11,000 --> 00:20:16,000
But if you shine blue light on them,
they fluoresce red.

242
00:20:16,000 --> 00:20:21,000
The chlorophyll in them fluoresces
red.  And these are the smallest and

243
00:20:21,000 --> 00:20:26,000
simplest photosynthetic cell.
They have 1,700 genes.

244
00:20:26,000 --> 00:20:29,000
And with that,
I call them the essence of life

245
00:20:29,000 --> 00:20:33,000
because with 1,
00 genes, they can convert CO2,

246
00:20:33,000 --> 00:20:37,000
nitrogen, phosphorus, all inorganic
compounds, basically this rock over

247
00:20:37,000 --> 00:20:41,000
here, in sunlight into life.
And this happens to be like that

248
00:20:41,000 --> 00:20:44,000
dominates the oceans.
They are the most abundant cell in

249
00:20:44,000 --> 00:20:48,000
the oceans.  In some areas,
it's about 50% of the total

250
00:20:48,000 --> 00:20:52,000
chlorophyll.  So,
they are basically a lean,

251
00:20:52,000 --> 00:20:56,000
mean photosynthesis machine,
and we're trying to understand

252
00:20:56,000 --> 00:21:01,000
everything about it.
OK, does a digression,

253
00:21:01,000 --> 00:21:09,000
hopefully not a diversion.
So, what regulates aquatic primary

254
00:21:09,000 --> 00:21:16,000
productivity?  Have to turn the
lights back on.

255
00:21:16,000 --> 00:21:24,000
Before we get into that totally,
I want to draw a typical, what we

256
00:21:24,000 --> 00:21:32,000
call a water column in
an aquatic ecosystem.

257
00:21:32,000 --> 00:21:36,000
And I have seen this little red,
sticky thing here.  This is from

258
00:21:36,000 --> 00:21:40,000
last year, and it says they don't
understand these axes.

259
00:21:40,000 --> 00:21:44,000
See, I remember from year to year.
So, if you don't understand

260
00:21:44,000 --> 00:21:48,000
something and doing,
because I can tell when students

261
00:21:48,000 --> 00:21:52,000
come up afterwards that I've
completely lost you.

262
00:21:52,000 --> 00:21:56,000
First of all, oceanographers plot
things upside down.

263
00:21:56,000 --> 00:22:00,000
So this is depth.  So,
depth goes down, which makes sense,

264
00:22:00,000 --> 00:22:05,000
right?
And then, whatever we are plotting

265
00:22:05,000 --> 00:22:11,000
against depth is on this axis.
So, in this graph I'm going to make,

266
00:22:11,000 --> 00:22:17,000
we are going to plot net primary
productivity, temperature,

267
00:22:17,000 --> 00:22:23,000
nutrients, a bunch of different
variables.  OK,

268
00:22:23,000 --> 00:22:29,000
and for oceans, this is about,
well, we'll just say 2,000 m, and

269
00:22:29,000 --> 00:22:36,000
for lakes, say, 200 m
for a deep lake.

270
00:22:36,000 --> 00:22:44,000
So, I'm drawing here sort of a
generic picture of a water column in

271
00:22:44,000 --> 00:22:52,000
either a lake or ocean.
OK, so do we have colored chalk?

272
00:22:52,000 --> 00:23:00,000
Not here, OK.  Sometimes it used to
float around.

273
00:23:00,000 --> 00:23:05,000
Well, you're going to have to use
your imagination.

274
00:23:05,000 --> 00:23:11,000
So first of all, let's plot light
as a function of depth.

275
00:23:11,000 --> 00:23:17,000
What does that look like?
Like that, exactly.  It's going to

276
00:23:17,000 --> 00:23:23,000
decay exponentially.
In lakes, this is about 10 m,

277
00:23:23,000 --> 00:23:29,000
and in oceans this is about 100 m.

278
00:23:29,000 --> 00:23:33,000
Oh, and this was a question somebody
gave in the instant feedback.

279
00:23:33,000 --> 00:23:38,000
Somebody said, I find it hard to
believe that all life in the oceans

280
00:23:38,000 --> 00:23:43,000
disappears where there is no more
light.  And, you're absolutely right.

281
00:23:43,000 --> 00:23:48,000
It's only the photosynthetic life
that disappears when there's no more

282
00:23:48,000 --> 00:23:53,000
light.  There's lots of life below
there that is using organic carbon.

283
00:23:53,000 --> 00:23:57,000
So, if you're here, that the answer
to your question.

284
00:23:57,000 --> 00:24:02,000
OK, so then, now we're going to
plot temperature which looks

285
00:24:02,000 --> 00:24:08,000
something like this.
And, this is what's called the

286
00:24:08,000 --> 00:24:14,000
[thermocline?].
And we can also think of this as

287
00:24:14,000 --> 00:24:20,000
density.  Because colder water is
more dense than warmer water,

288
00:24:20,000 --> 00:24:26,000
right, you must have learned that,
did you learn that somewhere?  Did

289
00:24:26,000 --> 00:24:33,000
you learn that somewhere?
Where did you learn that?

290
00:24:33,000 --> 00:24:40,000
Fourth grade, great,
well-prepared.  So, up on the

291
00:24:40,000 --> 00:24:47,000
surface we have biosynthesis here
where there's light,

292
00:24:47,000 --> 00:24:54,000
and so it's exactly the same
reaction as we have over here.

293
00:24:54,000 --> 00:25:02,000
And now it gets to the terrestrial
ecosystem.

294
00:25:02,000 --> 00:25:06,000
The production you have in the
surface water is you have

295
00:25:06,000 --> 00:25:10,000
phytoplankton photosynthesizing,
making organic matter.  They're

296
00:25:10,000 --> 00:25:14,000
being eaten by zooplankton,
by fish that are making feces,

297
00:25:14,000 --> 00:25:19,000
etc., that are being eaten by the
detritivores.  But the net effect of

298
00:25:19,000 --> 00:25:23,000
this teeming food web they saw in
the DVD last time,

299
00:25:23,000 --> 00:25:27,000
is that there's going to be organic
carbon that falls down

300
00:25:27,000 --> 00:25:33,000
below this lit zone.
OK, and that was the whale calling

301
00:25:33,000 --> 00:25:40,000
out to make, no,
not purposefully,

302
00:25:40,000 --> 00:25:47,000
but telling down and making carbon
available to the food web in the

303
00:25:47,000 --> 00:25:54,000
deep water.  So down here,
you have regeneration.  So this is

304
00:25:54,000 --> 00:26:01,000
light.  And this is in the
dark in the system.

305
00:26:01,000 --> 00:26:07,000
But it's directly analogous to the
biosynthesis and regeneration system

306
00:26:07,000 --> 00:26:13,000
there.  So the other thing we want
to plot on this is nutrients.

307
00:26:13,000 --> 00:26:20,000
They are drawn down to very low
levels in the surface water in the

308
00:26:20,000 --> 00:26:26,000
lit layer because the phytoplankton
are sucking them up.

309
00:26:26,000 --> 00:26:32,000
They are nutrient limited.
They're sucking up the nitrogen,

310
00:26:32,000 --> 00:26:38,000
phosphorus, et cetera.
And then, as the carbon and all of

311
00:26:38,000 --> 00:26:43,000
that range down to the deep water,
it's regenerated, and then the

312
00:26:43,000 --> 00:26:48,000
nutrients are regenerated.
So that's why you see the gradient

313
00:26:48,000 --> 00:26:53,000
of the low nutrients here and high
nutrients here,

314
00:26:53,000 --> 00:26:58,000
because the bacteria in the deep
water are breaking down the carbon

315
00:26:58,000 --> 00:27:03,000
and releasing them.
OK, so if we look at this map,

316
00:27:03,000 --> 00:27:08,000
we can see that for aquatic
ecosystems, obviously water

317
00:27:08,000 --> 00:27:13,000
is not limiting.
So water is an important regulator.

318
00:27:13,000 --> 00:27:19,000
Light is a very important regulator
of productivity down to about in

319
00:27:19,000 --> 00:27:25,000
this region.  And nutrients,
it turns out, are very important.

320
00:27:25,000 --> 00:27:31,000
And it's nutrients that really
determine the tapestry of this map

321
00:27:31,000 --> 00:27:37,000
that we're looking at.
And what I'm going to do for the

322
00:27:37,000 --> 00:27:45,000
rest of the class is explain it
lakes and oceans how the physical

323
00:27:45,000 --> 00:27:53,000
forces make these nutrients
available in certain regions more

324
00:27:53,000 --> 00:28:01,000
than in other regions and explain
this.  OK, so first let's look at

325
00:28:01,000 --> 00:28:07,000
lake ecosystems.
So, what we're showing here is a

326
00:28:07,000 --> 00:28:12,000
year in the life of a temperate lake.
So this might be the Mystic Lakes

327
00:28:12,000 --> 00:28:16,000
out in Arlington or something like
that.  Well, maybe that doesn't

328
00:28:16,000 --> 00:28:21,000
freeze over, I don't know.
But anyway, a lake that freezes

329
00:28:21,000 --> 00:28:26,000
over in the winter.
So let's start during the summer,

330
00:28:26,000 --> 00:28:31,000
and here's this basic graph showing
the thermocline,

331
00:28:31,000 --> 00:28:35,000
the nutrient depletion in the
surface, and this one indicates that

332
00:28:35,000 --> 00:28:40,000
you actually have oxygen depletion
in the deep water because of all of

333
00:28:40,000 --> 00:28:45,000
this organic matter from
productivity raining down and being

334
00:28:45,000 --> 00:28:50,000
consumed by heterotrophic organisms
that consume oxygen.

335
00:28:50,000 --> 00:28:54,000
So, as fall comes,
and this is the important part,

336
00:28:54,000 --> 00:28:59,000
in the summertime, this layer is
mixed.  So, it's isothermal.

337
00:28:59,000 --> 00:29:04,000
In the fall, you have the winds and
the surface cools.

338
00:29:04,000 --> 00:29:08,000
And as this density gradient here
starts to break down,

339
00:29:08,000 --> 00:29:12,000
do the cooling in the winds.
And so, you have this mixing.

340
00:29:12,000 --> 00:29:17,000
It's called fall overturn, which
[then trains?] these nutrients from

341
00:29:17,000 --> 00:29:21,000
the deep water into the surface.
So that's what way you get the

342
00:29:21,000 --> 00:29:26,000
nutrients for the deep water back up
into the surface,

343
00:29:26,000 --> 00:29:30,000
whereas in the summertime,
the gradient is maintained because

344
00:29:30,000 --> 00:29:35,000
of this density barrier,
and the mixing can't bring this down.

345
00:29:35,000 --> 00:29:39,000
And then in the winter,
you have the ice cover that

346
00:29:39,000 --> 00:29:44,000
obviously everything then is just
isothermal.  There's not much going

347
00:29:44,000 --> 00:29:49,000
on, but there is some photosynthesis.
And then in the spring,

348
00:29:49,000 --> 00:29:54,000
the surface waters start to warm up,
the ice melts, you have overturn,

349
00:29:54,000 --> 00:29:59,000
and brings the water up
from the deep water.

350
00:29:59,000 --> 00:30:03,000
In the ocean, in lakes,
this can mix all the way to the

351
00:30:03,000 --> 00:30:07,000
bottom, OK?  In the oceans,
there's no force of nature that can

352
00:30:07,000 --> 00:30:12,000
mix all the way down to 2,
00 m.  So you have this thermocline

353
00:30:12,000 --> 00:30:16,000
in the oceans,
but it's in a relatively small

354
00:30:16,000 --> 00:30:20,000
fraction of the total water column.
So the scale here is way off.

355
00:30:20,000 --> 00:30:25,000
We're going from 100 m down to 2,
00.  So in the ocean, it's just this

356
00:30:25,000 --> 00:30:29,000
tiny little, all this action in the
surface.  So we need another

357
00:30:29,000 --> 00:30:34,000
mechanism.  We can't mix all the way
down to the deep ocean.

358
00:30:34,000 --> 00:30:41,000
So, we need another mechanism for
bringing nutrients to the surface.

359
00:30:41,000 --> 00:30:49,000
And we're going to talk about,
there's four different ways.

360
00:30:49,000 --> 00:31:06,000
There's four different ways that the

361
00:31:06,000 --> 00:31:13,000
deep water nutrients are brought
back up where there is light,

362
00:31:13,000 --> 00:31:20,000
because you have to have liked for
photosynthesis to use the nutrients.

363
00:31:20,000 --> 00:31:27,000
And one is episodic mixing.  I'm
just going to list them,

364
00:31:27,000 --> 00:31:35,000
and then we're going to go through
them: coastal upwelling --

365
00:31:35,000 --> 00:31:45,000
-- equatorial upwelling,
and on much longer time scales,

366
00:31:45,000 --> 00:31:55,000
what's called the ìoceanic conveyor
beltî in quotes,

367
00:31:55,000 --> 00:32:05,000
which is basically local ocean
circulation.

368
00:32:05,000 --> 00:32:10,000
So let's go through these.
In the oceans, episodic mixing,

369
00:32:10,000 --> 00:32:15,000
let's go back.  Now, just pretend
this is an ocean,

370
00:32:15,000 --> 00:32:20,000
and that this goes down to 2,
00 m, and there's a thermocline.

371
00:32:20,000 --> 00:32:25,000
What happens in the oceans is that
you just have little,

372
00:32:25,000 --> 00:32:30,000
episodic mixing events that you
wrote a great here to get little

373
00:32:30,000 --> 00:32:36,000
bursts of nutrients injected
into the lit area.

374
00:32:36,000 --> 00:32:40,000
That's seasonal mixing,
but it never mixes all the way to

375
00:32:40,000 --> 00:32:45,000
the bottom.  And we can see,
I'll show you where, this right here

376
00:32:45,000 --> 00:32:50,000
is the north Atlantic's bloom.
And in the springtime, you see

377
00:32:50,000 --> 00:32:55,000
major bloom there due to this
episodic mixing in the North

378
00:32:55,000 --> 00:33:00,000
Atlantic, which have high winds and
a lot of mixing.

379
00:33:00,000 --> 00:33:05,000
OK, so there are also ocean currents
caused by this coastal upwelling

380
00:33:05,000 --> 00:33:10,000
phenomenon, especially along the
western coasts of continents.

381
00:33:10,000 --> 00:33:15,000
And I don't have time to go into
this.  You need a whole course and

382
00:33:15,000 --> 00:33:20,000
physical oceanography to really
understand this  because it has to

383
00:33:20,000 --> 00:33:25,000
do with the whole global ocean
circulation that causes this

384
00:33:25,000 --> 00:33:30,000
upwelling along the coasts.
But, I'm going to show you how this

385
00:33:30,000 --> 00:33:35,000
works in this movie,
or a little movie.

386
00:33:35,000 --> 00:33:40,000
I guess that's as dark as we're
going to get.  This is a

387
00:33:40,000 --> 00:33:46,000
cross-section of a coastal ocean.
So, here's the coastline.  Here's

388
00:33:46,000 --> 00:33:51,000
the surface of the ocean.
And these little molecules here are

389
00:33:51,000 --> 00:33:57,000
CO2.  Can you see blue?
This is probably not going to work

390
00:33:57,000 --> 00:34:02,000
because of this filming.
Well, we'll see what happens.

391
00:34:02,000 --> 00:34:06,000
OK, so going to go through it in a
still, and then I'll show the movie.

392
00:34:06,000 --> 00:34:11,000
But what you're going to see is as
blue patch upwelling along the coast

393
00:34:11,000 --> 00:34:15,000
here, in CO2 molecules are coming up
with it.  OK, here's the blue.

394
00:34:15,000 --> 00:34:20,000
That's nutrients, nitrogen,
phosphorus, etc.

395
00:34:20,000 --> 00:34:24,000
The wind is blowing offshore
causing the surface waters to move

396
00:34:24,000 --> 00:34:29,000
in that direction.
They have to be replaced by

397
00:34:29,000 --> 00:34:33,000
something, so we're bringing the
deep water up to replace that moving

398
00:34:33,000 --> 00:34:39,000
surface water.
And as that comes up,

399
00:34:39,000 --> 00:34:45,000
the CO2 comes up and is released.
And then you have a phytoplankton

400
00:34:45,000 --> 00:34:51,000
bloom from the nutrients,
and then the CO2 sucked back in

401
00:34:51,000 --> 00:34:57,000
again and you have oxygen going out.
And, here it goes, the movie.

402
00:34:57,000 --> 00:35:03,000
Upwelling: The Movie.
There comes the CO2.  Here are the

403
00:35:03,000 --> 00:35:09,000
nutrients.  CO2 out, CO2 back in.
These are phytoplankton,

404
00:35:09,000 --> 00:35:13,000
this green blobs.  That's a bloom.
So you have now the phytoplankton

405
00:35:13,000 --> 00:35:17,000
falling, big bloom,
organic carbon going down and being

406
00:35:17,000 --> 00:35:21,000
regenerated.  So,
it's a very dynamic system and

407
00:35:21,000 --> 00:35:25,000
that's why you have a lot of
high-intensity fisheries along the

408
00:35:25,000 --> 00:35:29,000
coasts, especially the western coast
of continents because of this

409
00:35:29,000 --> 00:35:33,000
upwelling; there's lots of nutrients,
lots of phytoplankton,

410
00:35:33,000 --> 00:35:38,000
lots of fish.
A dramatic example of the power of

411
00:35:38,000 --> 00:35:45,000
the surface currents,
and how they affect upwelling is

412
00:35:45,000 --> 00:35:51,000
this phenomenon called El NiÒo.
I think I'll skip the slide.  You

413
00:35:51,000 --> 00:35:58,000
don't have it in hand out,
anyway.  But here's an animation

414
00:35:58,000 --> 00:36:05,000
showing the changes in the
productivity in the Pacific Ocean

415
00:36:05,000 --> 00:36:12,000
along the equator.
Here's an El NiÒo.

416
00:36:12,000 --> 00:36:18,000
And I'll explain how that works in
a minute.  Here's a normal year

417
00:36:18,000 --> 00:36:24,000
where you have these phytoplankton
blooms, and let's look at it in this.

418
00:36:24,000 --> 00:36:30,000
You've seen this one before,
but let's look at it more closely.

419
00:36:30,000 --> 00:36:36,000
There's the equatorial bloom caused
by upwelling along the equator and

420
00:36:36,000 --> 00:36:40,000
are normally year.
And as we go around,

421
00:36:40,000 --> 00:36:44,000
this is like three years in the life
of the globe.  See,

422
00:36:44,000 --> 00:36:48,000
there is high productivity at the
Amazon where the Amazon's empty.

423
00:36:48,000 --> 00:36:52,000
Now, we are going to zoom in here,
and this is a normal year.  And

424
00:36:52,000 --> 00:36:56,000
that's an El NiÒo year.
You see, there's very little

425
00:36:56,000 --> 00:37:00,000
productivity, and is very little
upwelling along the coasts here.

426
00:37:00,000 --> 00:37:06,000
And that El NiÒo in Spanish,
what does it mean?  It refers to the

427
00:37:06,000 --> 00:37:12,000
Christ Child because this happens
around Christmastime roughly every

428
00:37:12,000 --> 00:37:18,000
seven years.  And what happens in a
phenomenon is it turned out that

429
00:37:18,000 --> 00:37:25,000
people have studied enough
for years.

430
00:37:25,000 --> 00:37:30,000
It's a global phenomenon in which
the prevailing currents in the whole

431
00:37:30,000 --> 00:37:35,000
Pacific Ocean shift from going in
this direction which causes the

432
00:37:35,000 --> 00:37:40,000
upwelling here to going in this
direction, which brings warm water

433
00:37:40,000 --> 00:37:46,000
suppressing the upwelling and
reducing the nutrient input into the

434
00:37:46,000 --> 00:37:51,000
system.  OK, so here's an El NiÒo
year, and directly compared to

435
00:37:51,000 --> 00:37:56,000
non-El NiÒo year.
And that's all due to physical

436
00:37:56,000 --> 00:38:02,000
force is changing the
nutrient delivery.

437
00:38:02,000 --> 00:38:10,000
So here's equatorial upwelling,
and then finally on a global scale,

438
00:38:10,000 --> 00:38:18,000
over very long periods of time, you
can imagine that these upwelling

439
00:38:18,000 --> 00:38:26,000
events would not be enough to bring,
you have this constant rain of

440
00:38:26,000 --> 00:38:35,000
organic matter coming from
the surface waters.

441
00:38:35,000 --> 00:38:38,000
And this nutrient reservoir in the
deep waters, none of these upwelling

442
00:38:38,000 --> 00:38:42,000
events are enough to bring all that
back and renew the system.

443
00:38:42,000 --> 00:38:45,000
So you need a bigger force than
that on a global scale over long

444
00:38:45,000 --> 00:38:49,000
time periods.  And that's what's
called the great oceanic conveyor

445
00:38:49,000 --> 00:38:53,000
belt.  And this is really important,
because I think people think of the

446
00:38:53,000 --> 00:38:56,000
oceans as a static,
understandably, you look out there;

447
00:38:56,000 --> 00:39:00,000
it looks like a bunch of water with
the surface waters and

448
00:39:00,000 --> 00:39:04,000
with the deep waters.
And if you throw something in the

449
00:39:04,000 --> 00:39:08,000
deep waters it's going to stay there
and you don't have to worry about it

450
00:39:08,000 --> 00:39:12,000
anymore.  A lot of people want to
bury nuclear waste in the deep water.

451
00:39:12,000 --> 00:39:16,000
And the point is that that's not
true.  The oceans are all

452
00:39:16,000 --> 00:39:20,000
interconnected,
and if I'm a water molecule,

453
00:39:20,000 --> 00:39:25,000
the average amount of time, and I'm
traveling with the currents,

454
00:39:25,000 --> 00:39:29,000
over a thousand years, I will make
this whole journey where I go along

455
00:39:29,000 --> 00:39:33,000
the surface waters and then I get to
the North Atlantic,

456
00:39:33,000 --> 00:39:37,000
and because the waters are cooled
and there's very high winds in the

457
00:39:37,000 --> 00:39:41,000
North Atlantic,
you have cold water and of the high

458
00:39:41,000 --> 00:39:45,000
winds cause high evaporation.
So you have saltier water,

459
00:39:45,000 --> 00:39:49,000
so, cold, saltier water up here
sinks.  And that actually is a force

460
00:39:49,000 --> 00:39:53,000
that drives this whole global
circulation.  And so,

461
00:39:53,000 --> 00:39:57,000
I'm cruising along here.
I get here, and I sink.  And then I

462
00:39:57,000 --> 00:40:01,000
go for this long journey down the
bottom.  And of course,

463
00:40:01,000 --> 00:40:04,000
it's much more complicated.
This is grossly oversimplified.

464
00:40:04,000 --> 00:40:08,000
But I go this long journey to the
bottom of the Atlantic in these deep

465
00:40:08,000 --> 00:40:12,000
ocean currents,
and then somewhere along the line,

466
00:40:12,000 --> 00:40:16,000
I get brought up again through zones
of upwelling here,

467
00:40:16,000 --> 00:40:20,000
or maybe I would meander up here and
get brought up again.

468
00:40:20,000 --> 00:40:24,000
[I'm just one atom on average?
.  So, through these global ocean

469
00:40:24,000 --> 00:40:28,000
currents, the deep water eventually
comes up to the surface,

470
00:40:28,000 --> 00:40:31,000
bringing those nutrients back.
Where it comes in contact with the

471
00:40:31,000 --> 00:40:35,000
light and the phytoplankton,
and they photosynthesize and they

472
00:40:35,000 --> 00:40:39,000
take up the nutrients and they make
organic carbonate,

473
00:40:39,000 --> 00:40:43,000
and it all settles down again to the
bottom.  So, it's a cycle.

474
00:40:43,000 --> 00:40:46,000
And if you didn't have that,
the thing would run down.  If you

475
00:40:46,000 --> 00:40:50,000
didn't have the deep water coming up
eventually coming up somewhere,

476
00:40:50,000 --> 00:40:54,000
the system would just run down and
you do have a big anoxic bottom of

477
00:40:54,000 --> 00:40:58,000
the ocean.  And who knows what would
happen?  So, this is

478
00:40:58,000 --> 00:41:03,000
really important.
OK, so finally,

479
00:41:03,000 --> 00:41:10,000
I've talked about nutrients just in
general, what nutrients are the most

480
00:41:10,000 --> 00:41:18,000
important?  And,
it turns out that there are some

481
00:41:18,000 --> 00:41:25,000
nutrients that are in much less
supply that are required by the

482
00:41:25,000 --> 00:41:33,000
plants.  And this is what's called,
so, what nutrients are important?

483
00:41:33,000 --> 00:41:41,000
Now, of course,
they're all important but some are

484
00:41:41,000 --> 00:41:50,000
more important in regulation than
others.  And there's something

485
00:41:50,000 --> 00:41:58,000
called the law of the minimum.
And it states that the growth of a

486
00:41:58,000 --> 00:42:10,000
plant will be limited --
-- by that element that is in least

487
00:42:10,000 --> 00:42:24,000
supply relative,
this is the important part,

488
00:42:24,000 --> 00:42:38,000
to the requirements of the plant or
the phytoplankton.

489
00:42:38,000 --> 00:42:43,000
When I say plant,
it could be phytoplankton or a tree,

490
00:42:43,000 --> 00:42:48,000
or a plant, or whatever.  And this
is the important part.

491
00:42:48,000 --> 00:42:53,000
So how we figure out what the
requirements for elements are above

492
00:42:53,000 --> 00:42:58,000
plants?  You might grab it,
harvested, grind it up, and measure

493
00:42:58,000 --> 00:43:04,000
the ratio of the elements
in that plant.

494
00:43:04,000 --> 00:43:09,000
So, for example,
if you do that, for most plants you

495
00:43:09,000 --> 00:43:15,000
get something on the order of,
at least for most phytoplankton,

496
00:43:15,000 --> 00:43:21,000
which are my  preferred plant, you
get the ratio of carbon,

497
00:43:21,000 --> 00:43:27,000
nitrogen, and phosphorus,
of 106 atoms of carbon [for?

498
00:43:27,000 --> 00:43:33,000
16 nitrogen per one of phosphorus.
So this tells you in what ratio they

499
00:43:33,000 --> 00:43:41,000
need these elements in order to grow.
So then you look in the environment

500
00:43:41,000 --> 00:43:49,000
and you ask, what are the ratios
available?  So,

501
00:43:49,000 --> 00:43:57,000
say if the water has a ratio of,
what's going to be the most living

502
00:43:57,000 --> 00:44:05,000
element in that system
for that plant?

503
00:44:05,000 --> 00:44:12,000
Exactly, nitrogen.
And, alternatively,

504
00:44:12,000 --> 00:44:19,000
you could have something like this.
And what would be limiting there?

505
00:44:19,000 --> 00:44:26,000
Phosphorus limits.
And it turns out that in most

506
00:44:26,000 --> 00:44:33,000
aquatic ecosystems,
for now we're going to say that

507
00:44:33,000 --> 00:44:40,000
nitrogen and phosphorus are the
important limiting factors.

508
00:44:40,000 --> 00:44:44,000
And just to show you,
again, that ecologists do

509
00:44:44,000 --> 00:44:48,000
experiments, here's an experimental
lakes area in Ontario,

510
00:44:48,000 --> 00:44:52,000
where there are 22 different lakes
set aside for research.

511
00:44:52,000 --> 00:44:56,000
And in this particular set of lakes,
this is a control lake,

512
00:44:56,000 --> 00:45:00,000
and this is the experimental lake.
They added phosphorus to the lake.

513
00:45:00,000 --> 00:45:05,000
And you can see the phytoplankton

514
00:45:05,000 --> 00:45:09,000
bloom by only adding phosphorus.
They didn't add anything else.  And

515
00:45:09,000 --> 00:45:14,000
that means that phosphorus was in
least supply relative to the other

516
00:45:14,000 --> 00:45:18,000
nutrients.  And the interesting
thing that happened here was that

517
00:45:18,000 --> 00:45:23,000
when they added the phosphorus,
that makes phosphorus in great

518
00:45:23,000 --> 00:45:27,000
abundance relative to nitrogen.
And what that did is make nitrogen

519
00:45:27,000 --> 00:45:32,000
the limiting factor.
And when nitrogen is the limiting

520
00:45:32,000 --> 00:45:37,000
factor, what organisms might
have an advantage?

521
00:45:37,000 --> 00:45:40,000
We talked about them.
Yeah, there you go, nitrogen fixing

522
00:45:40,000 --> 00:45:44,000
organisms.  So,
if nitrogen is limiting,

523
00:45:44,000 --> 00:45:47,000
only organisms that can take it from
the atmosphere can get more nitrogen

524
00:45:47,000 --> 00:45:51,000
than the other organisms.
So they are favored.  And what

525
00:45:51,000 --> 00:45:54,000
happens is you fertilize with
phosphorus.  You get blooms of

526
00:45:54,000 --> 00:45:58,000
nitrogen fixing organisms.
It's really an interesting

527
00:45:58,000 --> 00:46:02,000
phenomenon.
But nitrogen and phosphorus are,

528
00:46:02,000 --> 00:46:06,000
one or the other is limiting in
lakes.  And in large areas of the

529
00:46:06,000 --> 00:46:10,000
oceans, nitrogen and phosphorus are
also limiting,

530
00:46:10,000 --> 00:46:14,000
except we've learned recently that
there are areas of the oceans where

531
00:46:14,000 --> 00:46:19,000
iron is actually a limiting factor.
And this was an experiment that was

532
00:46:19,000 --> 00:46:23,000
done by oceanographers.
And there is Alaska just to get you

533
00:46:23,000 --> 00:46:27,000
oriented.  This is the North Pacific
where they went out with a boat and

534
00:46:27,000 --> 00:46:31,000
they made it a patch.
They added iron just to a patch of

535
00:46:31,000 --> 00:46:36,000
ocean.
And I can tell you about this.

536
00:46:36,000 --> 00:46:40,000
We were involved in some of these
experiments.  It started out with a

537
00:46:40,000 --> 00:46:45,000
10 km x 10 km patch and showed that
if you add iron you get a bloom of

538
00:46:45,000 --> 00:46:49,000
phytoplankton.
And this is a satellite image of

539
00:46:49,000 --> 00:46:54,000
that phytoplankton bloom.
And in the last lecture, I'm going

540
00:46:54,000 --> 00:46:59,000
to tell you all about those iron
fertilization experiments,

541
00:46:59,000 --> 00:47:03,000
and the implications for how we are
going to use the oceans

542
00:47:03,000 --> 00:47:08,000
in the future.
So, take-home messages: we'll talk

543
00:47:08,000 --> 00:47:12,000
about that next time.
You can take them home,

544
00:47:12,000 --> 00:47:15,000
but I don't want to keep you over.