​​​AICE Marine Science: Topic 1 Water

one oxygen (-) and two hydrogen (+)

Draw a water molecule

chlorine atom gains one electron ; sodium atom loses one electron ;to fill / complete outer (valency) shell ;

opposite charges (of ions) attract (to form lattice) ;

Explain the formation of sodium chloride (NaCl)

Water molecules pull the sodium and chloride ions apart, breaking the ionic bond that held them together. After the salt compounds are pulled apart, the sodium and chloride atoms are surrounded by water molecules, as this diagram shows. Once this happens, the salt is dissolved, resulting in a homogeneous solution

How sodium chloride dissolves in water

as depth increases, salinity increases

explain the relationship between depth and salinity

runoff, evaporation, precipitation, ice formation, and ice melting.

Factors affecting salinity

decrease the density of seawater

effect of high temperature on density on seawater

increases the density of seawater

effect of higher salinity on density of seawater

amount of oxygen dissolved in water

Dissolved Oxygen (DO)

Partial charges on water molecules allow water to interact with charged ions and covalent substances

Capable of forming bonds with unusually large number of substancesbstances d

Why is water the universal solvent?

as water heats up, it increases the kinetic energy making it easier for water molecules to break the ionic bonds and surround the positive and negative ions that are left.

Impact of higher temperature of seawater on the rate of dissolution of salts increases.

0 degrees Celsius

freezing point of water

The higher the concentration of salt, the lower the freezing point drops.

Impact of salinity on freezing point

Hydrogen bonds (H-bonds) reduce density

Water molecule movement slows

H-bonds between water molecules strengthen

Stronger H bonds able to keep water molecules at perfectly symmetrical distance from each other forming crystal lattice

Fewer water molecules able to fit in same volume

Density is reduced in the solid → ice

Why does Ice Float?

Due to number of hydrogen bonds in liquid water

Allows water to act as temperature buffer and climate regulator globally

Size of oceans allows them to hold a tremendous amount of heat energy before the water will change temperature

Keeps coastal climates mild, impacts rain patterns, influences wind

Why does water has one of the highest specific heat capacities

when a body of water has a salinity level greater than 40 ppt

Hypersaline

evaporation, formation of sea ice

What increases salinity?

precipitation, runoff from land, icebergs melting, sea ice melting

What decreases salinity?

Most hypersaline environment on Earth

Don Juan Pond in Antarctica

numeric value expressing the acidity or alkalinity of a solution

Symbol for 'potential of hydrogen'

Abiotic factor within ecosystems

Particularly important for aquatic ecosystems like the ocean

Used to measure the concentration of hydrogen ions in a liquid

pH

A substance that increases the hydrogen ion concentration of a solution.

Acid

a compound that produces hydroxide ions in solution

Base

Ratio of H+ : OH-

determines the pH of a solution

pH meter or data-logging pH probe.

limitations: probe must be cleaned between each reading and reading must be taken from same depth

How to measure pH quantitively?

8.1

What is the current pH of the ocean?

nitrogen, oxygen, carbon dioxide

Major gases in the atmosphere and ocean

irregular changes in the speed and direction of fluid movement due to wave action causes mixing at the surface of the ocean

Turbulence

the concentration within seawater increases

As concentration of gas in atmosphere increases

high due to due to ability to form carbonic acid when mixed with water

solubility of carbon dioxide

low Does not chemically combine with water molecules

solubility of oxygen

The temperature is inversely proportional to the solubility of the gas in a liquid, hence for all gases, as the temperature increases, solubility decreases accordingly.

Explain the solubility of gases in relation to water temperature.

Less molecule movement

Better able to dissolve more gases (higher solubility)

more dense

greater depths

higher salinity

cold water

More molecule movement

Easier for dissolved gas molecules to leave water and enter atmosphere

Gas molecules are less soluble in warm water

surface ocean

absorbs incoming radiation (warmer)

less dense

warm water

solubility increases due to

why?

Higher pressure → higher concentration of gases → gases forced into the water (increases solubility)

As atmospheric pressure increases

solubility decreases

why?

Lower pressure → lower concentration of gases in atmosphere → more gases escape the seawater (decreases solubility)

As atmospheric pressure decreases

Gases dissolve better in water with low to no salinity

Because fewer solutes are taking up the spaces available to the gases

Allows for more interaction between water molecules and gases

How does salinity impact solubility?

freshwater>estuary> open ocean

Where are gases more soluble?

a layer of water in which the salinity changes rapidly with changes in depth

Halocline

the layer within the ocean where the concentration of dissolved oxygen is at its lowest, typically found between 100 and 1000 m deep

oxygen minimum layer

Greatest DO concentration in top 100m

at what depth is the DO the most saturated?

Turbulence / mixing of water

Photosynthesis by producers (i.e. algae, phytoplankton)

oxygen is a by-product

Why does the surface have the highest DO?

the zone that receives enough light to allow photosynthesis to occur

photic zone (ocean)

necessary for photosynthesis

Why is CO2 important?

Used by all living organisms for respiration

Why is O2 important?

Transformed into ammonia (NH3) by bacteria

Makes nitrogen usable for other organisms

Needed for amino acids & proteins, DNA & RNA

Why is nitrogen gas important?

mass/volume

Density

kg/m³

unit of density

temperature changes drastically

In tropical seas the thermocline is steep as water temperature at the surface can be 25°C or higher, while water at 2000m and greater is at 1°C

In polar seas there is less likely to be a thermocline at all

Temperature gradient is subtle

Little difference between temperature at surface and in deep waters

Thermocline in tropical waters (low latitudes)

In polar seas there is less likely to be a thermocline at all

Temperature gradient is subtle

Little difference between temperature at surface and in deep waters

thermocline in polar regions (high latitude)