Download Chemistry of Water

Chemistry of Water
Salinity

An expression of the amount of salt in a fixed
amount of seawater.
Expressed as ppt (parts per thousand) 0/00
 Parts per thousand literally means “x” amount of solutes
per thousand parts of water.



Remember that solutes are the ;substances being dissolved by
water , which is the universal solvent. A Salts are hydrophillic
meaning they love water!
Salinity varies over the surface of the oceans. The salinity
at any particular spot depends on what processes or
factors are operating at that location that either add or
remove water.
Factors Affecting Salinity

Salinity decreases when
water is added


High amounts of rain,
melting sea ice, river
input)
Salinity increases when
water is removed

High evaporation, sea-ice
formation
Salinity

At depth, salinity remains the same in all oceans.
Between the sruface and deep water however, is
a region called a halocline. This is the area of
the water where salinity gradulally increases or
decreases with depth.

Salinity is also high in enclosed or partiallyenclosed basins (such as the Mediterranean)
Where does the Salt come from???


Salt in oceans exist in the form of dissolved ions,
some positively charged, and some negatively
charged.
There are 6 types of salt ions found in the ocean:
Most common (85% of sea salt): Na (sodium), Cl
(chloride), both components of table salt.
 Sulfate (SO4)
 Magnesium (Mg)
 Calcium (ca)
 Potassium (K)


Regardless of how salty the water is… they are all
found in definite proportions….
Principle of Common Proportions

Discovered by Alexander
Marcet in 1819 (17701822), a swiss chemist and
doctor who performed
some of the earliest
research in marine
chemistry

Stated that all the main
chemical ions in seawater
are present in exactly the
same proportions
throughout the world’s
oceans.
Where does the salt come from?

Salts have gotten into oceans in the following
ways:
Dissolved out of rocks on land and were carried to
oceans in surface run-off
 From underwater hydrothermal vents
 From dust or volcanic ash blown from land

Sinks




There are also “sinks” for every type of ion.
SINKS: processes that remove dissolved ions
from seawater, such as salt spray onto land, or
the falling of ions onto the seafloor as mineral
deposits.
Each type of ion has a certain length of time in
which it will stay dissolved in water before it is
removed, or sinks.
The MOST COMMON ions in seawater will remain
dissolved for a FEW HUNDRED years to hundreds
of MILLIONS of years!
Temperature

Surface temperatures vary widely across the globe
according to the amount of heating from the sun
Tropical areas are warmer than polar areas, and remain
warmer throughout the year because of constant
heating from the sun.
 In the middle latitudes, there is more seasonal changes
in surface temperature.
 In hugher latitudes and polar oceans, the water is
constantly cold, often below 32 degrees F.

Thermocline

Below the surface: the water
drops quickly to about 46-50
degrees F at 3,300 feet.
3300 ft. down - Region of steep
decline in temperature (called
the thermocline)
 Temperature drops more as you
go deeper, but at a slower rate,
until the sea floor (constant 36
degrees around the globe)

Density

Depends on two things:
 Temperature – as water warms, it expands,
decreasing density, below 4 degrees C, water
becomes a little less dense (remember it freezes at 0
degrees C, and floats on water)
 Salinity – as salinity rises, density increases, because
the salt molecules can occupy spaces between the
water molecules
 Density increases with depth because of changing
temperatures of the water


This drives the ocean currents: It drives large scale circulation of water in
the oceans between the surface and deep water.
The Denser/Cooler masses sink and move slowly toward the equator. The
colder, high density deep and bottom waters comprise 80% of the total
volume of the ocean!




Seawater in the world's oceans has a salinity of about 3.5% (35 g/L, or
599 mM). This means that every kilogram (roughly one liter by volume)
of seawater has approximately 35 grams (1.2 oz) of dissolved salts
(predominantly sodium (Na+) and chloride (Cl−) ions).
Average density at the surface is 1.025 g/ml. Seawater is denser than
both fresh water and pure water (density 1.0 g/ml @ 4 °C (39 °F))
because the dissolved salts add mass without contributing significantly
to the volume.
The freezing point of seawater decreases as salt concentration
increases. The coldest seawater ever recorded (in a liquid state) was in
2010, in a stream under an Antarctic glacier, and measured −2.6 °C
(27.3 °F).[2]
The most saline open sea is the Red Sea, where high rates of
evaporation, low precipitation and river inflow, and confined
circulation result in unusually salty water. The salinity in isolated bodies
of water (for example, the Dead Sea) can be considerably greater still.
WHICH IS SALTIER??
ATLANTIC OR PACIFIC
• On average, the Atlantic is the saltiest of the world's major oceans; the salinity of the
surface waters in the open ocean ranges from 33 to 37 parts per thousand (3.3 - 3.7%) by
mass and varies with latitude and season.
• Surface salinity values are influenced by evaporation, precipitation, river inflow, and
melting of sea ice. Although the minimum salinity values are found just north of the
equator (because of heavy tropical rainfall), in general the lowest values are in the high
latitudes and along coasts where large rivers flow into the ocean.
• Maximum salinity values occur at about 25° north and south of the equator, in
subtropical regions with low rainfall and high evaporation.
• The Pacific ocean Salinity also varies latitudinally.
• Water near the equator is less salty than that found in the mid-latitudes because of
abundant equatorial precipitation throughout the year.
• Poleward of the temperate latitudes salinity is also low, because little evaporation of
seawater takes place in these frigid areas.
SALTIEST WATER IN
WORLD???




The saltiest water in the world is in the Red Sea (that is actually a lake)
where the high atmospheric temperatures causes rapid evaporation. Its
salt content is 40 parts per thousand.
The saltiest ocean in the world is the Atlantic. Along the Atlantic coast
the salinity ranges from 33 parts per thousand off Cape Cod to about
36 off the coast of Florida.
The saltiest part of the Atlantic is an area of about two million square
miles south of Bermuda called the Sargasso Sea. The only sea in the
world completely surrounded by an ocean. Its salinity content is a bit
below that of the Red Sea.
The average salinity of all the oceans is about 3.49 parts per thousand.
Gases and Nutrients in
Bodies of Water
Gas Exchange

What are the main gases in H2O?

Dissolved gases such as;


nitrogen, oxygen, and carbon dioxide.
Why is Oxygen highest near the surface?

Levels of oxygen and carbon dioxide vary depending
on how many phytoplankton- microscopic organisms
that perform photosynthesis, and the activity of other
aquatic animals in the area that are respiring.
Oxygen: Most soluable in colder water

Highest levels are near the surface

1. oxygen in the atmosphere is diffusing into the water



Diffuses into colder surface waters, so higher oxygen
2. Phytoplankton found living in the top layers, and in
high numbers here, producing oxygen from
photosynthesis
Levels drop as you go deeper, but then rise again
once you get past 3300 ft.

Click here for simulation
Carbon Dioxide: The ocean stores 50 times
more Carbon dioxide than the atmosphere does

Highest levels are at depth, and lowest levels are at
the surface
1. phytoplankton live in high numbers at the surface and
use large amounts of carbon dioxide for photosynthesis
 2. Carbon dioxide diffuses out of the water and into the
atmosphere
 3. Carbon sink: Many aquatic organisms make shells out of
carbonate, a compound of carbon and oxygen. When they
die, their shells may fall to the ocean floor, and become
sediments and rocks over time.
 Click here for simulation

Carbon Cycle
The Ocean Carbon Cycle

1. Physical Pump: due to CO2 dissolving into sea
water, CO2 dissolves into cold ocean water at high
latitiudes. It is carried to the deep ocean by sinking
currents, where it stays for hundreds of years.
Eventually, mixing brings the water back to the
surface. The ocean emits CO2 into the atmosphere
in tropical areas. This system of deep ocean
currents is a “physical pump” for carbon, it helps
pump carbon from the atmosphere into the sea for
storage.


2. Biological Pump: due to Phytoplankton converting CO2
into carbohydrates from photosynthesis. Animals eat
phytoplankton, dead animals and the phytoplankton dink
towards the bottom of ocean “marine dnowfall” and some
lands on the floor, along with other matter… dead fish, fecal
matter, etc… and a small amount of carbon is eventually
buried and stored in the sediments and can remain for
millions of years. This is called the carbon sink.
BUT some of the carbon is used by animals and bacteria for
making shells, reefs, etc… and is eventually returned to the
deep ocean part of the carbon cycle… this is the biological
pump.
Phytoplankton

What are they?


Microscopic floating life-forms that obtain energy by
photosynthesis, they need nitrates, iron, and
phosphates to grow and multiply.
Why are they important?
Form the base of every aquatic food chain
 Provide 80% of the world’s oxygen
 Continue the nutrient cycle flow


Green areas indicate high plankton numbers.
What does this say about the type of water
plankton prefer? (shallows)
Phytoplankton Growth

What determines their rate of growth?
The amount of available nutrients in the
water (nitrates, iron, and phosphates)
 Blooms occur if the supply of nutrients
rapidly increases.


Sometimes, Red Tides occur, which can
cause mass fish kills.
RED TIDES



Red tides, known as, Harmful algal blooms, or HABs, occur when
colonies of algae—simple ocean plants that live in the sea—grow out of
control while producing toxic or harmful effects on people, fish,
shellfish, marine mammals and birds. These algae, known as
phytoplankton, are single-celled protists, plant-like organisms Certain
species of phytoplankton, dinoflagellates, contain photosynthetic
pigments that vary in color from green to brown to red.
One of the best known HABs in the nation occurs nearly every summer
along Florida’s Gulf Coast. This bloom, like many HABs, is caused by
microscopic algae that produce toxins that kill fish and make shellfish
dangerous to eat. The toxins may also make the surrounding air difficult
to breathe. As the name suggests, the bloom of algae often turns the
water red
Not all are harmful, most blooms, in fact, are beneficial because the tiny
plants are food for animals in the ocean. In fact, they are the major
source of energy that fuels the ocean food web.
Phosphate Distribution in Ocean




The growth of plants in the shallows use up available
phosphates in the sediments.
The plants containing this phosphate are then eaten by other
organisms. Most of these organisms the return to deeper
water.
When they die, their bodies are decomposed by the actions of
bateria, which releases the phosphates to these deeper parts
of the ocean.
The phosphate in the deeper levels is returned to the depleted
shallow waters by the process called upwelling. The longer a
section of deep water stays within the deeper parts of the
ocean, the more phosphate it will accumulate.
Nitrogen Distribution in Ocean





Atmospheric Nitrogen (N2) is the MOST abundant form of nitrogen on Earth.
However, most organisms can’t use it in that form
Bacteria exist in the water to switch the nitrogen gas (N2) into a usable form first as
ammonia(NH3), in the process of nitrogen fixation, then changed into nitrates(NO3)
in the process of nitrification. This usually occurs in high oxygen content areas such
as in the surface layers of the ocean. NO3 is found in the surface waters and are used
by phytoplankton.
The nitrogen is passed along the food chain and when the organisms die, the nitrogen
in their bodies returns to the water as their bodies decay from bacteria actions. The
nitrogen in deeper layers is returned through upwelling.
Denitrification: occurs in benthic or bottom layers of the ocean where there is little
available dissolved oxygen. It involves bacteria using the NO3, rather than the O2,
during respiration (fermentation), the end results is that the NO3 is returned to the
form of N2 which cycles the nitrogen gas back into the atmosphere.
Nitrogen Cycle

Click here for simulation
DEAD ZONES



Dead zones are areas where the bottom water (the
water at the sea floor) is anoxic — meaning that it has
very low (or completely zero) concentrations of
dissolved oxygen.
These dead zones are occurring in many areas along
the coasts of major continents, and they are spreading
over larger areas of the sea floor.
Because very few organisms can tolerate the lack of
oxygen in these areas, they can destroy the habitat in
which numerous organisms make their home.
DEAD ZONES



The cause of anoxic bottom waters is fairly simple: the
organic matter produced by phytoplankton at the surface of
the ocean (in the euphotic zone) sinks to the bottom (the benthic
zone), where it is subject to breakdown by the action of
bacteria, a process known as bacterial respiration.
The problem is, while phytoplankton use carbon dioxide and
produce oxygen during photosynthesis, bacteria use oxygen
and give off carbon dioxide during respiration.
The oxygen used by bacteria is the oxygen dissolved in the
water, and that’s the same oxygen that all of the other
oxygen-respiring animals on the bottom (crabs, clams,
shrimp, and a host of mud-loving creatures) and swimming
in the water (zooplankton, fish) require for life to continue.
CAUSES OF DEAD ZONE


The apparent cause of the creeping dead zones is
agriculture, specifically fertilizer. While fertilizer is
necessary to foster bumper agricultural crops, it also
runs off the fields into the streams and rivers of a
watershed.
When the fertilizer reaches the ocean, it just
becomes more nutrients for the phytoplankton, so
they do what they do best: they grow and multiply.
Which leads to more organic matter reaching the
bottom, more bacterial respiration, and more anoxic
bottom water.
OTHER CAUSES???




There is another interesting aspect to zones of anoxia—not all areas
with anoxic bottom water are caused by pollution.
The largest "dead zone" on the planet is the entire Black Sea below a
depth of about 150 meters.
Due to the fact that the exchange of water in the Black Sea with the
Mediterranean Sea is limited to the flow through the narrow Bosporus,
all of the mixing of freshwater and seawater takes place in the upper
150 meters, because the freshwater entering from rivers is less dense
than seawater.
Below the pycnocline (a density boundary where the water density
increases abruptly), the Black Sea water column is entirely anoxic,
down to the bottom 2000 meters below. Special sea Cameras can’t see
that deep, but it can get a good image of the Black Sea on a clear day.