Chapter 3

Chemical and Physical Features

of Seawater

Water for life…

Water facts…•Most cells are 70-95% water

•Three-quarters of the earth’s surface is covered by water.

•Water is the only common substances that can be found in all 3 physical states (solid, liquid or gas) within earth’s temperature range.

•Less than 1% of the earth’s water is freshwater.

•Water makes life possible, as we know it, on earth.

What is it about water that makes it a suitable medium for life?

Most of the properties that make water suitable for life are related to water’s ability to form hydrogen bonds

Hydrogen bondingWater is polar because of the unequal sharing of electrons in the bond between H and O in a water molecule.

The attraction between opposite dipoles of separate water molecules is a hydrogen bond.

dipoles

Recap important features…

• Polar covalent bonds• Hydrogen bonds• electronegativity

Water cycle

Discovery education- cycles

• http://www.etap.org/demo/biology_files/lesson6/instruction4tutor.html

What role does water play in the carbon cycle??

• Ocean is called a carbon sink • Carbon dioxide is dissolved in large

amounts in the ocean• Source is primarily cellular

respiration and burning fossil fuels

Phases of water

• Solid- ice (molecules not moving around)

• Liquid- water (molecules moving around with some speed)

• Gas- water vapor (molecules moving around very fast, too fast to form H bonds)

Organisms depend on the cohesion and adhesion of water molecules

Surface tension!

• Cohesion- H bonds attract water molecules to each other

• Adhesion- water “sticks” to other materials

Surface tension

• “skin like” surface of water.• Due to H-bonds- HIGH surface tension• Water’s resistance to objects

attempting to penetrate its surface• Individual H bonds are weak compared

to covalent bonds but the bonds have cumulative strength in numbers

• Viscosity- the tendency for a fluid to resist flow (colder, the “thicker” it is because more molecules in a space). This allows plankton to use less energy to stay afloat

The cohesive nature of water molecules allows water to resist temperature change…

Specific heat is the amount of heat needed to change the temperature of a substance by 1 degree Celsius.

Specific heat of H2O = 1 calorie (cal) to raise 1 g by 1 degree C

Specific heat of water

• HIGH due to hydrogen bonds• Water will change its temperature

less when it absorbs or loses a given amount of heat

• WHY? Much of the heat is used to break the H bonds before molecules can begin moving faster

High specific heat relevance to life

• 1. A large body of water can absorb and store a huge amount of heat from the sun in the daytime and during summer while warming only a few degrees. At night and during the winter, the gradually cooling water can warm the air

• 2. stabilizes ocean temperatures creating favorable environment for marine life

• 3. since organisms are made primarily of water, they are better able to resist changes in their own temperature than if they were made of a liquid with a lower specific heat

Sssooooo…….

• Water that covers the earth keeps temperature fluctuations on land and in water within limits that permit life

Heat Capacity

• Water has the highest latent heats of melting and evaporation and one of the highest heat capacities of any natural substance.

• Latent Heat of Melting and Evaporation

Fastest molecules (with most energy) break free of bonds. Slower ones left behind = lower temp.

How does H-bonding affect temperature change?

Water molecules tend to “stick together” through H-bonding. Much of the energy that goes into a body of water must first go into breaking these bonds before temperature (i.e. “molecular movement”) can increase.

What implications does water’s high specific heat have for living systems?

Large bodies of water can absorb lots of heat from the sun and change temp. very slowly!

Living organisms are made mostly of water which stabilizes body temperature.

Water has a high heat of vaporization…

…it takes a great deal of heat to get water to boil (go from liquid to gas phase).

Water’s heat of vaporization = 580 cal/g/0C

Evaporative cooling!

Ice is less dense then liquid water…

Why ice floats

• Less dense as a solid than as a liquid

• Water expands when freezing

Density

• Density = mass / volume• Density is affected by

– Temperature– Pressure– Salinity

– Water is less dense as a solid

Lower density and LIFE…

• If ice sank, then eventually all ponds, lakes, and oceans would freeze solid making life as we know it impossible

• During summer, only the upper few inches of the ocean would thaw

INSTEAD……

• When a deep body of water cools, the floating ice insulates the liquid water below, preventing it from freezing and allowing life to exist under the frozen surface

Salinity and Density

• Salinity varies with depth• Density differences cause water to

layer• High density lies below low density

Water: the solvent of life

• Solution- a liquid that is a completely homogeneous mixture of two or more substances

• Solvent- dissolving agent• Solute- substance that is dissolved• Not “universal solvent”- if it were, it

would dissolve any container in which it was stored. “versatile solvent” due to polarity

Water is a versatile solvent…

table salt

Review- 4 Emergent Properties of water

• Cohesive behavior• Ability to moderate temperature• Expansion upon freezing• Versatility as a solvent

BozemanBiology

• Properties of Water• http://www.youtube.com/watch?v=

DVCYlST6mYQ

Seawater

• Nature of pure water• Materials dissolved in it• Seawater contains a little of almost

everything• Solutes = dissolved materials (ex.

ions in seawater)• Solvent = liquid doing the dissolving

Rule of Constant Proportions

• The relative amounts of the various ions in seawater are always the same!

• For seawater; no matter how much salinity varies, proportions of key inorganic elements stays the same

• Only water amount and therefore salinity changes

Salt composition in seawater

• Salinity- the total amount of salt dissolved in seawater

• Salinity is expressed in the number of grams left behind when 1,000 g of seawater are evaporated

• Ex. 35g left from evaporating 1,000g water (35ppt) 35%

• Average salinity of the ocean is about 35 ppt

• Open ocean varies at 33-37 ppt depending on the balance between evaporation and precipitation

• Salinity of water greatly affects the organisms that live in it

• Most marine organisms die in fresh water

• Even slight changes in salinity harm them

Pg 72: salinity, osmosis and diffusion

• Osmosis• Diffusion• Concentration gradient• Hypertonic• Hypotonic• Isotonic

• WHY DO FISH DRINK SEAWATER???

• Answer in caption figure 4.14

• Many marine organisms are highly affected by changes in salinity. This is because of a process called osmosis which is the ability of water to move in and out of living cells, in response to a concentration of a dissolved material, until an equilibrium is reached. In general the dissolved material does not easily cross the cell membrane so the water flows by osmosis to form an equilibrium. Marine organisms respond to this as either being osmotic conformers (also called poikilosmotic) or osmotic regulators (or homeosmotic).

Did you write this?????

• Marine organisms respond to this as either being osmotic conformers (also called poikilosmotic) or osmotic regulators (or homeosmotic).

Page 74: regulation of salt and water balance

• Osmoconformers- internal concentrations change as the salinity of the water changes

• Osmotic conformers have no mechanism to control osmosis and their cells are the same salt content as the liquid environment in which they are found (in the ocean this would be 35 o/oo salt). If a marine osmotic conformer were put in fresh water (no salt), osmosis would cause water to enter its cells (to form an equilibrium), eventually causing the cells to pop (lysis). If a marine osmotic conformer were put in super salty water (greater than 35 o/oo salt) then osmosis would cause the water inside the cells to move out, eventually causing the cells to dehydrate (plasmolyze).

Hagfish- osmo conformers

• Osmoregulate- control their internal concentrations to avoid osmotic problems. Adjust solute concentration in their body to match that of the environment

• Osmotic regulators have a variety of mechanisms to control osmosis and the salt content of their cells varies. It does not matter what the salt content is of the water surrounding a marine osmotic regulator, their mechanisms will prevent any drastic changes to the living cells. Marine osmotic regulators include most of the fish, reptiles, birds and mammals. These are the organisms that are most likely to migrate long distances where they may encounter changes in salinity. An excellent example of this is the salmon fish. The fish is about 18 o/oo salt so in seawater it tends to dehydrate and constantly drinks the seawater. Special cells on the gills (called chloride cells) excrete the salt so the fish can replace its lost water. When a salmon migrates to fresh water its cells start to take on water so the salmon stops drinking and its kidneys start working to produce large amounts of urine to expell the water.

Do fish drink water???

• http://www.whfreeman.com/Catalog/static/whf/phelanpreview/doc/01_fish.pdf

Osmoregulation

salt water

35 ppt

fresh water

0-5 ppt

The problem of osmolarity:

salt water

35 ppt

fresh water

0-5 pptFISHES

The problem of osmolarity:

Hyper-osmotic

Hypo-osmotic

salt water

35 ppt

fishes are either:

stenohaline - tolerant of limited range of osmolarity

euryhaline - tolerant of wide range (where is this useful?)

fresh water

0-5 pptFISHES

The problem of osmolarity:

Hyper-osmotic

Hypo-osmotic

1. osmo-conformers (hagfishes)

2. salt supplementers (marine elasmobranches and coelacanths)

3. hyposmotics (marine teleosts)

4. hyperosmotics (freshwater fishes)

excrete large volumes of water

gill chloride cells pump in salts

often euryhaline (striped bass, tilapia, drum)

How fish deal with being osmotic misfits

Osmoregulation example

• Sharks• Adjust amount of urea in blood• Dunaliella can live in freshwater or

water with 9 times saltier than normal seawater

• single celled marine algae• Figure 4.15 Sea Turtle

BozemanBiology Osmoregulation Video

• http://www.youtube.com/watch?v=qfWx8msgHqM

• Only first 3 minutes 50 seconds

Bull shark-osmoregulation

• http://www.youtube.com/watch?v=E9kkfX1d6N4

• National geographic video 2:53

Earth: The Water Planet

• http://www.youtube.com/watch?v=moSBExlLu2M

Colligative Properties of Seawater

• Properties of a liquid that are altered by presence of solute

• 1. ability to conduct electrical current

• 2. decreased heat capacity (less heat to raise temp)

• 3. raised boiling point (boils at higher temp)

• 4. decreased freezing temp (freezes at lower temp)

• 5. slowed evaporation (due to attraction between ions and water)

• 6. ability to create osmotic pressure (water exists in lower concentration than in freshwater)

Salinity review

• Page 44• Solutes• Salinity• Rule of constant proportions• *salinity is the total quantity of all

dissolved INORGANIC solids, not just salt)

Salinity

• Ocean salinity varies almost entirely as a result of the addition or removal of pure water rather than the removal of salts

• Why are icebergs not salty? • Page 44

Water cycle review

• Water is added to the ocean by precipitation (rain and snow) and to a lesser extent by the melting of glaciers and polar ice

• Six solutes (ions) compose 99% of seawater: see table 3.1

Those 6 are…..

• Chloride (55% of total salinity)• Sodium (30.59% of total salinity)• Sulfate• Magnesium• Calcium• potassium

Why is the sea salty?

• Freshwater minerals and chemicals dissolving and flowing to ocean via precipitation, erosion, waves, surf, and hydrothermal vents

Drinking ocean water

• http://www.youtube.com/watch?v=iSJggIWlH9w

Ions in sea water figure 3.6

• Not all ions in seawater enter the ocean at the same place

• Positive ions like sodium and magnesium come from weathering rocks and are carried by rivers

• Negative ions like chloride and sulfide enter at hydrothermal vents and volcanos

Average salinity

• The average salinity of the ocean is 35ppt

• Open ocean is about 33ppt-37ppt

Variations in Salinity

• Variations occur in ocean salinity due to several factors:

• 1. most common factor is the relative amount of evaporation or precipitation in an area. If there is more evaporation than precipitation then the salinity increases (since salt is not evaporated into the atmosphere). If there is more precipitation (rain) than evaporation then the salinity decreases

• 2. Another factor that can change the salinity in the ocean is due to a very large river emptying into the ocean. The runoff from most small streams and rivers is quickly mixed with ocean water by the currents and has little effect on salinity. But large rivers (like the Amazon River in South America) may make the ocean have little or no salt content for over a mile or more out to sea.

• 3. The freezing and thawing of ice also affects salinity. The thawing of large icebergs (made of frozen fresh water and lacking any salt) will decrease the salinity

Dissolved Gases

• Oxygen = O2

• Carbon Dioxide= CO2

• Nitrogen= N2

• All Three are found in atmosphere and dissolve into ocean at surface

nitrogen

• Required for protein, nucleic acids and chlorophyll

• Makes up 78% of air and 48% of gases dissolved in sea water

• Nitrogen fixation- bacteria absorb nitrogen and put it into chemical compounds organisms can use

Gas exchange

• When the reverse occurs and the sea surface releases gases to the atomosphere

Pg 47

• Gases dissolve better at colder water (polar) – Why?

• As the temperature decreases, so does the kinetic energy of any particle

• The gas as a lower energy and thus cannot escape the water

• Solubility decreases with increase of temperature

• The concentration of dissolved oxygen and carbon dioxide are very important for marine life forms. Although both oxygen and carbon dioxide are a gas when outside the water, they dissolve to a certain extent in liquid seawater.

Gases in the Ocean page 47

• CO2 makes up 80% of gases in ocean. In air it is only .04%. (reacts chemically when dissolved)

• Most important gases are: oxygen, carbon dioxide, and nitrogen

• “gas exchange” between atmosphere and ocean

Dissolved oxygen

• Oxygen is not very soluble• Less oxygen in water than in air• Susceptible to oxygen depletion by

respiration

• Gases dissolve better in cold than warm, so dissolved gas concentrations are higher in polar waters than the tropics

• Dissolved oxygen is what animals with gills use for respiration (their gills extract the dissolved oxygen from the water flowing over the gill filaments). Dissolved carbon dioxide is what marine plants use for photosynthesis.

temperature

• Temps in the open ocean varies between -2C and +30C (28 F and 86F)

• Temp varies more than salinity• The temperature and salinity of

seawater determine its density. It gets denser as it gets saltier, colder, or both

Temp, density, climate

• http://www.youtube.com/watch?v=qeZgJzt3m04

Transparency

• One of the most biologically important properties of seawater

• All photosynthetic organisms need light to grow

• Figure 3.11 show colors of the visible spectrum and the depths of penetration

What are the colors of the visible spectrum?

• ROYGBIV• In clear ocean water, blue light

penetrates the deepest, red light the least

• Figure 3.12 page 47

Page 47

• Photosynthesis equation• Cellular respiration equation

Pressure page 48

• Pressure changes with depth• On land, we are under 1

atmosphere (14.7 pounds psi)• Marine organisms are under the

weight of the water and the atmosphere…..and water is heavier than air

• With each 10 m (33 ft) of increased depth, another atmosphere of pressure is added

• Added pressure compresses gases• Figure 3.15

14.7 psi every ATM

480 ATM at 3 miles down for 7,056 psi

Acidity and Alkalinity

• pH measures• Relative concentration of positively

charged H ions and negatively charged OH

• Acidic=many H ions. pH less than 7• Alkaline- many OH ions. pH more

than 7

pH…

• pH changes with depth due to the amount of carbon dioxide

• Shallow- pH 8.5• Middle- pH lower due to more carbon

dioxide• Deep- more acidic due to no photosynthesis• At 3,000 M and deeper, it becomes even

more acidic due to sinking organic material decay

• The oceans are not, in fact, acidic, but slightly basic. • Acidity is measured using the pH scale, where 7.0 is

defined as neutral, with higher levels called "basic" and lower levels called "acidic".

• Historical global mean seawater values are approximately 8.16 on this scale, making them slightly basic.

• To put this in perspective, pure water has a pH of 7.0 (neutral), whereas household bleach has a pH of 12 (highly basic) and battery acid has a pH of zero (highly acidic).

• However, even a small change in pH may lead to large changes in ocean chemistry and ecosystem functioning. Over the past 300 million years, global mean ocean pH values have probably never been more than 0.6 units lower than today (6). Ocean ecosystems have thus evolved over time in a very stable pH environment, and it is unknown if they can adapt to such large and rapid changes.

journal

• http://www.ocean-acidification.net/FAQacidity.html#AcidicOA

• Answer the 4 questions at the top

Density and temperature experiment

• http://www.youtube.com/watch?v=_Ww6BIy3nc0

• (red water, blue water, explaining density and currents)