Hello marine biology students.
In this video we have just a bit more to discuss
about the properties of water.
[Intro Music]
Temperature isn't the only unique
feature of water.
Water is also a solvent, meaning that other
materials dissolve into water.
Water is known as a universal solvent 
because it's so good at dissolving various
types of salts.
Any substance dissolved in water is known
as a solute.
Ocean water has solutes dissolved in the water.
The level of solutes is called its salinity.
So here we see how ionic substances can easily
dissolve into water, because of those partial
positive and partial negative charges of the
water molecule.
They can surround the ions with the opposite
charge and allow those ions to dissociate
from each other.
The main solutes dissolved in seawater are
chloride and sodium, giving seawater it's
salty taste, however there are several other
solutes as well.
Now, the ratio of the solutes in seawater
are remarkably consistent, even when the overall
salinity can vary in different water masses.
Looking at this chart, we can see the common
ions in seawater include chloride and sodium,
sulfate, magnesium, calcium and potassium.
And these percentages are remarkably consistent,
so fifty five point zero three percent of
the ions dissolved in seawater consistently
will be chloride ions.
Likewise thirty point five nine percent of
the ions dissolved in seawater are going to
be sodium, with diminishing amounts of the
other ions, yet they are detectably there.
They are consistently present in specific
percentages, and again, what's surprising
is that it doesn't matter if the total salinity
of the seawater is 32 parts per thousand or
37 parts per thousand, this ratio between
the ions will be consistent.
The salinity of seawater 
is normally around 35 parts per thousand,
but it can vary by location.
Now salinity is measured in parts per thousand
instead of percent or part per hundred so
that means for every 1000 grams of water there
are 35 grams of salts.
Ocean water near a location where a river
meets the sea can be as low as 15 to 25 parts
per thousand whereas other areas might be
higher if evaporation is high
and there are no rivers bringing fresh water
or there's not a significant amount of precipitation.
Water is also relatively transparent 
to light.
This means that sunlight shining on the surface
can penetrate
the surface, crucial for photosynthetic organisms
living underwater.
This level of penetration varies greatly depending
on the amount of particles in the water.
Many biologists can use tools to quantify
how clear water is.
One of these tools is known as a Secchi Disc.
So here we see an image of what a Secchi disc
looks like.
It's usually a circular structure with white
and black sections connected to a rope.
You lower the rope down far enough until the
sections on the disc are no longer distinguishable
from each other, just based on sight.
You can then measure the length of rope that
you would use to lower the Secchi disc and
that gives you a measure of the visibility
of the water.
So maybe one day you're able to lower the
Secchi disc down 20 meters and still and just
then lose the distinction between the black
and white sections.
Another day, it might only be five meters.
These types of measurements for water clarity
are important in marine biology.
It turns out that different wavelengths of
light
are absorbed by water and its particles at
different levels.
Blue light is able to travel the farthest
into the water without being absorbed, while
red light is absorbed very quickly.
Many marine organisms that live in dark environments
will have red pigments as a form of camouflage.
Now, we don't often think of red as being
a typical camouflage pigmentation color, but
when you live in an environment that does
not have red light, it will not be reflected.
And so, here we can see a picture of the sea
star that was filmed about 30 meters or 90
feet down, with under natural lighting conditions
and you can see the very ends of it sort of
blend in to its surroundings.
That same sea star with a picture using an
electronic flash, clearly we can see the red
ends to its appendages.
There's a very impressive video that I want
you to check out after this one about color
and aberration correction for underwater photography.
I have the link here and we'll also have the
video itself in our Canvas page.
When we talk about the things being added
to the oceans, these can be solutes and water,
and it turns out that most of the water enters
the ocean either through precipitation like
rain and snow or also from rivers, and the
rivers are returning precipitation that had
fallen on the land.
To a far lesser extent, you might say that
water is being added by polar ice, but that
is a reduced amount.
Solutes or salts are added to the ocean from
the weathering of rocks, from hydrothermal
vents within the ocean and volcanic activity
above the ocean surface as well.
And then also solutes delivered from rivers
from land runoff.
So when we look at these various sources,
whether we're talking about sulfide ions and
chloride ions which primarily come from volcanic
activity or sodium, potassium and magnesium
which come from erosion, these are where a
lot of those solute components of seawater
come from.
And again, the water itself is coming in the
form of rain and snow and also river runoff.
Gas is able to dissolve into liquid water
and so there are many gases that are dissolved
in sea water.
These are primarily the gases that are found
in our atmosphere, being oxygen gas, carbon
dioxide, and nitrogen gas.
Gas from the atmosphere dissolve into the
seawater at the sea surface.
Now, occasionally the reverse, known as off
gassing, also occurs, where deep-sea water
comes up with a different combination of gases
and releases those gases into the atmosphere
at the sea surface.
Many organisms 
in the ocean utilize oxygen and release carbon
dioxide.
Unlike solutes, gases are more soluble in
cold water and less soluble in warm water.
If you think of a can of soda and the carbon
dioxide that's dissolved into it, the cold
soda will hold its bubbles for much longer
time than a warm soda.
Again, that just has to do with the solubility
of gases in liquids.
Another aspect to realize is that the column
of seawater is not going to be exactly the
same throughout its entire depth.
Conditions at the ocean floor in the water
column and at the surface can differ greatly.
For that reason, marine biologists will also
often want to know what the conditions are
like at different points of the water column,
whether it's oxygen content, temperature,
salinity, and other factors.
They're often very different from one depth
to another.
Pressure is something that will also increase
as one travels farther down the water column
and this is because the water at the bottom
has the weight of all the water above it pushing
down on it, which means that organisms living
down deep in the water column also experience
this pressure.
A way that a marine biologist might get information
about water at different depths in the water
column is by making a series of collections
using Niskin bottles.
Now, this can be done electronically today,
but in the past it was a manual, physical
process of getting temperature readings at
these great many deaths.
We can also see that pressure varies by increasing
in one atmosphere for every 10 meters.
That takes us to the end of our discussion
of water and its properties.
Wow that was a lot of information.
Definitely don't hesitate to review this video
at another time.
Watch certain sections again to understand
these concepts of what makes water so unique.
Now, a question I want you to think about
before our next video is “Has the water
in the Atlantic Ocean ever been in the Pacific
Ocean?”
That's going be our question.
All right, see you in the next video!
