Chapter 6 Oceanography

• Low pressure and high evaporation creates areas of low salinity

• High pressure and low evaporation creates areas of high salinity

Chloride = 19.35 g/kg and 18.87 g/L

Sodium = 10.76 g/kg and 11.05 g/L

Sulfate = 2.71 g/kg and 2.78 g/L

Magnesium = 1.29 g/kg and 1.32 g/L

Calcium = 0.41 g/kg and 0.42 g/L

Potassium = 0.39 g/kg and 0.40 g/L

• 35 g/kg

• 36.07 g/L

• Trace elements: occur in minute or trace amounts

• Concentration is parts per billion ppb, (e.g., µg/kg) or lower

• Despite their low concentration, some are very important for life thriving in the ocean (e.g., Fe, ZN)

  • Others may be considered pollutants (e.g., Pb, Hg)

• All elements on Earth can be found in seawater

Salinity is regulated by:

• Sources of dissolved substances (inputs)

• Evaporation and precipitation, deposition, precipitation (outputs or sinks)

As things are added to the seawater an equal amount is removed

The ion residence time determines its concentration in the ocean

• Longer residence time = higher concentration

Salinometer (left)

• Seawater conducts electricity and the conductivity is proportional to the amount of salt

Conductivity-Temperature-Depth Recorder (right)

• Can be lowered on a wire

• Can be mounted on a buoy

The bending of light in the water is proportional to the density.

• Saltier the water, the denser it is; hence, the greater the light refraction

Determine chlorinity and calculate salinity

• Cl- is precipitated as AgCL

• Salinity (g/kg) = 1.80655 x chlorinity (g/kg)

Photosynthesis

• 106 CO2 + 122 H2O+ 16 HNO3 + H3PO4 => (CH2O)106(NH3)16H3PO4 + 138 O2

• Carried out by plants in sunlit surface oceans

• Consumes CO2 and nutrients, and produces O2 and organic material

Respiration = OM degradation

• (CH2O)106(NH3)16H3PO4 + 138 O2 => 106 CO2 + 122 H2O+ 16 HNO3 + H3PO4

• Carried out by all living organisms in surface and deep water

• Consumes O2 and organic material and produces CO2 and nutrients

Where do the gasses go if they come out of solution?

• Atmosphere

• Depth where there is as much oxygen produced by photosynthesis as consumed by respiration

• Net change in oxygen concentration is always 0!

• Particles are formed at the surface by photosynthesis

  • Particles sink

• OM will be degraded at depth, increasing CO2 concentration in deep water

  • Oxygen concentration decreases due to respiration

• Deep water formed at surface where there is an equilibrium between the water and the oxygen in the atmosphere

  • The oxygen found in this water then sinks to deep water untouched

• Carbonate shells can be redissolved or buried in sediments

• CO2 has been moved from the surface water to deep water by the falling particles = biological pump

• Marine algae (plants) need nutrients to grow

  • Nitrogen: Nitrate (NO3-), nitrite (NO2-), ammonium (NH4+)

  • Phosphorus: Phosphate (PO42-)

  • Silica: Silicate (SiO4-)

• Nutrient concentrations will be low in surface waters with actively growing algae

• Nutrients are transported to deep water by sinking particulate organic material (dead plants and animals)

  • Part of biological pump

• Heterotrophic bacteria will degrade the material; (decomposition and respiration) as it sinks and in sediments on the ocean floor => nutrient are released in the process => nutrient concentrations increase in deeper waters

Why is the concentration low at the surface?

• Photosynthesis occurs at the surface which uses nutrients

Why is the concentration higher at depth?

• More cellular respiration occurs here which produces nutrients

Why does the concentration decrease a little again towards deeper waters?

• Deep water is formed at the surface so that water at the surface with a low nutrient concentration travels down to become deeper water

Molar abundance shows concentration of atoms not weight

• CO2 is actually about 0.04% in the atmosphere now

• Differences in solubility

• Ocean has taken up a lot of CO2 that humans have released into the atmosphere

H+: the negative exponent increases as something becomes basic

• Increasing pH numbers means decrease in H+

• Low pH is high concentration of H+

OH-: the negative exponent decreases as something becomes more basic

• Increasing pH numbers means increase in OH-

• Low pH is low concentration of OH-

The H+ and OH- concentrations for pure water and blood cancel each other out because they are equal, hence why they are neutral

• CO2 cycle is important in the context of global warming -determines how much CO2 accumulates in the atmosphere

  • Green numbers tell us how much mass is held by each reservoir

  • Black numbers on arrows tell us how big a flux is

  • If the mass in a reservoir is to remain the same, as much mass has to be added as is removed

  • If a reservoir has more mass added than is removed there is a parenthesis in the white box, indicating the amount of annual increase.

• Over historical time, the reservoirs have been in balance, i.e. their respective sizes have not changed. This is not true anymore.

• The figure shows us that CO2 concentration is increasing in the atmosphere, the surface ocean, and the deep ocean.

  • Caused by fossil fuel burning and cement production

    • Fossil fuel burning is by far the most important.

• The atmospheric CO2 concentration increase causes CO2 to dissolve into the surface ocean

  • CO2 is eventually also transported into the deep sea

  • Increasing oceanic CO2 concentrations causes a decrease in pH, also known as ocean acidification

• The carbonate system buffers seawater pH 

• Atmospheric CO₂ dissolves in the surface ocean

• CaCO₃ dissolves in deeper waters

• Most carbonate is present as HCO₃^-

  • CO₂ + H₂O ⇄ H₂CO₃

  • H₂CO₃ = H⁺ ⇄ HCO₃^-