oceanography

Structure of H2O:

• 2 hydrogen atoms bonded to an oxygen atom with a covalent bond

• The bent shape gives water its properties

• Water molecules are held together by hydrogen bonds

• polar

• Water is molecule 

  • = uneven distribution of  charge

    • Oxygen atom has a neg(--) charge

    • Hydrogen atoms have a pos(+) charge

• “Universal” Solvent

• • Polar molecules are attracted to other polar molecules

  • Solvent = the thing that does the dissolving (water)

  • Solute = the thing that gets dissolved (salt, sugar, calcium, etc)

  • Solution = the solvent + the solute

• Does water really dissolve everything? 

  • Better term would be “Most Versatile Solvent”

Cohesion

• tendency of molecules of the same kind to stick to one another

  • Result of hydrogen bonds between water molecules

  • Creates surface tension on bodies of water, which allows the surface of water to stretch and not break easily

Adhesion

attraction between molecules of a different types

capillary action

which allows water to move from the roots of plants to the leaves, or blood to flow through veins & arteries

Temperature

• • The most important physical factor affecting life in the oceans

  • Sea surface temps vary from 32-86^oF

  • Salt lowers the freezing point, so seawater freezes at 30^oF

  • Ocean temperature decreases (gets colder) as depth increases

  • Thermocline = change in temperature with depth

Heat Capacity

• Water has a HIGH

• the amount energy needed to raise the temperature of a substance

•  AKA specific heat

• Also means water has a high heat of vaporization – it takes a lot of heat energy to get water to change states of matter (solid 🡪 liquid 🡪 gas)

Latent Heat

• heat absorbed or released during changes in states of matter

• has HIGH , which is related to its high heat capacity

• Heat of Melting/Freezing = energy needed to break or form the bonds between water molecules in ice (ice = liquid water)

• Heat of Vaporization/Condensation = energy needed to break or forms bonds between liquid water molecules (liquid water = gas/water vapor)

• Heat of Evaporation= energy needed to convert water to a gas below the boiling point

acids, bases , neutral

• a substance that donates H+ ions to a solution

  • Solution will have a higher # of H+ ions

  • Results in pH below 7

• substance that donates OH- ions to a solution

  • Solution will have a higher # of OH- ions

  • Results in pH above 7

• solution has an = # of H+ ions & OH- ions

  • Results in pH of 7 (pure water)
    
    

pH Scale

• describes how acidic or basic a solution is

  • 0 – 6.9 = acids

  • 7 = neutral

  • 7.1 – 14 = bases / alkaline

• Seawater is slightly alkaline (basic)

  •  Surface water average pH 8.1

• Ocean water pH decreases with depth

Buffering

• keeps ocean from becoming too acidic or too basic.

  • A buffer returns a solution to its original pH

• Calcium carbonate (CaCO₃) is the ocean’s buffer

Transparency

• (can see through it)

• Means sunlight can reach organisms that need it for photosynthesis

• How far down sunlight can reach depends on materials dissolved & suspended in the water

  • Water clarity is dictated by turbidity = measure of the degree water loses its transparency due to presence of suspended particles.

    • AKA: How clear or cloudy the water is

    • The more particles suspended in the water, the higher the turbidity (the cloudier or less transparent it is)

      • Muddy water = high turbidity

Pressure

• Increases with ocean depth (the deeper you go, the more pressure there is)

• Marine organisms are under more pressure than those on land

• As pressure ↑ gases are compressed

  • Means gas-filled structures in marine organisms shrink/collapse as they swim deeper

  • Limits the depth range of these organisms

Salinity

• total amount of dissolved solids in water (also includes dissolved gases) 

  • Measured in parts per thousand (ppt /  ⁰/₀₀)

    • Average ocean salinity = 35 ppt

    • Chloride (Cl-) and Sodium (Na+) = most prevalent ions in sea water

      • 85-90% of dissolved ocean ions

    • Other ions: 

      • Magnesium (Mg)

      • Potassium (K)

      • Sulfate (SO₂-)

      • Calcium (Ca)

• Salinity Variations

• • Brackish = influx of fresh water from rivers or rain lowers salinity

    • Often in coastal estuaries

  • Hypersaline = more salt than water

    • Great Salt Lake salinity = 280 ^o/_oo.

    • Dead Sea salinity = 330 ^o/_oo.  

• Varies with changes in latitude

  • High latitudes (near the N & S poles) = low salinity due to sea ice melting, precipitation & runoff

  • Mid latitudes (near the Tropics of Cancer & Capricorn) = high salinity due to warm, dry, descending air increasing evaporation

• Low latitude (near Equator) = low salinity due to high precipitation & runoff

  • Within the different latitudes, salinity varies with depth

    • High latitudes = salinity increases as depth increases

    • Low latitudes = salinity decreases as depth increases

  • Deep ocean salinity is relatively constant

  • Halocline = change in salinity with depth

• Processes Affecting Salinity

• Removing water from the ocean increases salinity

  • Evaporation = water evaporates, but salts stay behind

  • Sea ice formation = salts do not freeze with the water, so remaining water has a higher salinity

    • Adding water to the ocean decreases salinity

      • Runoff = adds fresh water to the ocean from land, diluting the seawater

      • Precipitation = adds fresh water to the ocean in the form of rain, diluting the seawater

      • Sea ice melting = adds the fresh water frozen in the ice, diluting the seawater

Density

• the amount of matter in a given volume

  • (How tightly “packed” the molecules are)

  • Water is less dense as a solid because it expands as it freezes

  • Means ice is less dense than liquid water, so it floats!

  • Pycnocline= change of density with depth

Carbon & Ocean Chemistry

• The ocean absorbs CO₂ from the atmosphere

• It is a carbon sink = a natural system that sucks up and stores CO₂  from the atmosphere

  • Physical & biological processes move CO₂  to the deep ocean where it is stored

  • Carbon sequestration = capture & storage of carbon

  • Human activity releases extra CO₂ into the atmosphere

  •  Too much CO₂ could harm marine organisms & ecosystems

  • When CO₂ dissolves in seawater, it produces carbonic acid

   CO₂ + H₂O ↔ H₂CO₃

• This carbonic acid dissociates in the water, releasing hydrogen ions and bicarbonate

H₂CO₃ ↔ H⁺ + HCO₃^--  

Ocean Acidification

• The increase in hydrogen ions cause an increase acidity

• This results in ocean acidification = ongoing decrease in pH of oceans

  • Caused by increased uptake of human-produced CO₂ from atmosphere

Humans & Carbon Dioxide

• About 35–45% of the carbon dioxide released by humans into the atmosphere dissolves into the oceans, rivers and lakes

  • Pollution

  • Electricity

  • Industrial growth

  • Transportation (gasoline)

  • Burning of fossil fuels (coal)

  • The increased release of CO₂ is released into the atmosphere and then absorbed by the ocean

  • This results in an increase in carbonic acid, which dissociates in the water, releasing hydrogen ions, which results in...

  
  

  … A ↓ IN pH

  
  

How Does Ocean Acidification Affect Coral Reefs?

• One result of the release of hydrogen ions is that they combine with any carbonate ions in the water to form bicarbonate:

H⁺ + CO₃^2-- ↔ HCO₃^—

• This decreases the amount of carbonate available to marine organisms

• Calcium carbonate = the material that composes the shells and exoskeletons of many marine organisms

  • Without the carbonate, marine organisms cannot make their shells or exoskeletons
    This affect the coral’s ability to grow its limestone skeleton (which is made out of CaCO₃)

    • Leads to slower growth of the reef & more fragile structural support,

    • Makes it more vulnerable to erosion

    • The breakdown of the corals’ limestone skeleton = gradual loss of corals on a reef

Biogeochemical Cycles: 

Process by which abiotic materials move from the atmosphere or soil into organisms and back again. 

• Water Cycle 

• Carbon-Oxygen Cycle

• Nitrogen Cycle 

Water Cycle

• Water never stops moving

• Most cycling occurs through transpiration, evaporation, and precipitation

  • Water gets into soil through precipitation and runoff, picked up by plants, which are consumed by animals and then given back to atmosphere through respiration and decomposition

Carbon Cycle

• Photosynthesis removes CO₂ from the air and adds O₂. 

• Cellular respiration removes O₂ from the air and adds CO₂. 

  • Photosynthesis and respiration usually balance out. 

• Decomposers break down organic material releasing CO₂. 

• Increased levels of CO₂ in the atmosphere trap more heat and increase the possibility of global warming. 

• Carbon enters the living (biotic) world through the action of autotrophs (photosynthesis)

• Carbon returns to the atmosphere and water by 

  • respiration (as CO₂) 

  • burning 

  • decay (producing CO₂ if oxygen is present, methane)

Nitrogen cycle

• Nitrogen is in the atmosphere (N2) and is converted by bacteria into a form that can be used by plants.  The plants convert it into a form that can be used by animals.  It is returned to the atmosphere when they decay and die.

• Nitrogen Fixation – nitrogen gas (N₂) is changed into ammonia (NH₃)

  • Atmospheric fixation by lightning

  • Biological fixation by certain microbes

• Decay

  • Organic nitrogen compounds return to the environment as ammonia

• Nitrification

  • Nitrifying bacteria make nitrogen available to the roots of plants

• Denitrification

  • Reduces nitrates to nitrogen gas, thus replenishing the atmosphere