Notes from Class Unit 2

Light Transfer in the Ocean

Heat Transfer

Radiation: Energy transfer to the ocean from the sun.
- Light travels as electromagnetic radiation.
- We use the Electromagnetic Spectrum to describe light.
- Violet light is more energetic than red light.
- Shorter wavelengths of light contain more energy.

Light Penetration and Attenuation

Light Attenuation describes the total decrease in light penetration in the water column.
- Absorption: Light energy is converted into other forms of energy (e.g., heat).
  - This is the primary process by which phytoplankton (primary producers), plants, or inorganic and organic molecules absorb light energy.
- Scattering: Light changes direction as it reflects off particles.
  - This creates 2D images of the seafloor.

Factors Affecting Solubility

Speed of Sound: Varies in seawater and is affected by various factors.
- Axial modulus describes how well water compresses.
- A higher axial modulus means the substance is harder to compress (i.e., less compressible).

Light Zones in Seawater

Upper Panel: 0-100m
Middle Panel: 0-1000m

Sonar uses:

Sound navigation and ranging.
It measures distance by using reflected sound.
Average speed of sound in seawater is 1500 m/s.
Average speed of sound in air is 334 m/s.
Seismic reflection profilers use sound waves to make 2D images of the seafloor.
Bathymetry (Mapping bottom type in 3D) is used in oceans and rivers.

Freshwater vs. Saltwater

Freshwater:

Is less dense than seawater.
Has lower thermal capacity.

Saltwater:

Has higher thermal capacity.
Moves approximately 5 times faster than sound in air.
The speed of sound in seawater is faster than in freshwater.
The speed of sound in seawater at 20°C is 1500 m/s.

Sound Navigation and Ranging (Sonar)

Sonar is a technology primarily used for sound navigation and ranging.
It uses reflected sound waves to measure distances.
The average speed of sound in seawater is approximately 1500 m/s.
The average speed of sound in air is approximately 334 m/s.
Seismic reflection profilers use sound waves to create 2D images of the seafloor.
Bathymetry describes bottom type mapping and 3D images.
Used in oceans and rivers.

Salinity and the Hydrologic Cycle

Isohaline: A line connecting points of equal salinity in the ocean.
The distribution of salinity is not uniform.
Hydrologic Cycle Input of H₂O (freshening process):
- Precipitation
- Melting ice
- River flow
Hydrologic Cycle Output of H₂O (salinification process):
- Evaporation
- Freezing
Surface Salinity Factors:
- Low Salinity: Occurs in zones of high precipitation (e.g., tropical and temperate regions).
- High Salinity: Occurs in zones of high evaporation (e.g., deserts at sea level, generally between 25°N and 60°S latitude).

Fisheries Biology

Main message: "Feed them us."
Focuses on visualizing and understanding food layers (tuna, for example).
NaCl (sodium chloride) dissolves in water.

Key Takeaways

Salinity is influenced by the input and output of water.
Higher evaporation leads to higher salinity.
Higher precipitation leads to lower salinity.

Water as a Universal Solvent

Water (H

₂O) is considered a universal solvent due to its unique physical properties. It continuously dissolves ions from land runoff, such as through rivers. Water flows off the land where salinity decreases. Polar regions exhibit higher salinity because when ice forms, impurities (salts) are expelled. Notably, the major dissolved ions in seawater are generally not removed or significantly impacted by organisms.

Major Constituents of Seawater

Six ions collectively make up 99% of the dissolved solids in seawater:

Chloride (Cl⁻)
Sodium (Na⁺)
Sulfate (SO₄²⁻)
Magnesium (Mg²⁺)
Calcium (Ca²⁺)
Potassium (K⁺)

Types of Constituents

Conservative Constituents (Ions)
- These are elements or salts whose ratios and total salt content do not change significantly in seawater.
- They exhibit relatively constant concentrations with depth.
- Their concentrations are largely consistent because they are not actively used or removed by biological activity or chemical reactions.
- Example: Sodium (Na⁺), Chloride (Cl⁻)
Non-Conservative Constituents
- These constituents are modified by biological and chemical processes.
- Their concentrations can vary spatially (e.g., with depth and location) and temporally.
- Often present at much lower concentrations than conservative ions.
- Examples: Dissolved gases (Oxygen, Carbon Dioxide, Nitrogen), Nitrates, Phosphates.
- Their levels can be altered or limited by biological and chemical processes (e.g., uptake by organisms, decomposition).

Calculating Chloride Concentration

Given a total salinity of 35 parts per thousand (ppt) or grams/kilogram (g/kg):

The fraction of Chloride (Cl⁻) in total salt is found using the ratio:

$X = \frac{19.344 \text{ g/kg Cl⁻}}{35 \text{ g salt/kg}}$

The calculation to determine the amount of Chloride (Cl⁻) in a given amount of salt based on its known proportion is:

$X = (19.344 \text{ g/kg Cl⁻} \times 42) / 35 \text{ g/kg}$

$X = 23.21 \text{ g/kg Cl⁻}$

Nutrients in Seawater: Non-Conservative, Biogeochemically Important Elements

These inorganic limiting nutrients are crucial for phytoplankton growth.

Nitrogen (N)
- Exists in 3 forms: Nitrate ( $\text{NO}_3^-$ ), Nitrite ( $\text{NO}_2^-$ ), Ammonium ( $\text{NH}_4^+$ ).
- Is consumed by phytoplankton.
- Is produced by excretion and decomposition.
Phosphorus as Phosphate ( $\text{PO}_4^{3-}$ )
Other Trace Nutrients & Elements ( $\text{Fe}$ and others)
- Silicoflagellates require silica.
- Nitrogen (N) or Phosphorus (P) can be limiting nutrients.

Non-Conservative Constituents and Biological Processes

Biological material is consumed and then produced/excreted by heterotrophs (like zooplankton, fish, crabs, shrimp, turtles, sharks, etc.).
Heterotrophs cannot photosynthesize; they produce inorganic carbon and consume autotrophs.

Nutrient Residence Times

Nutrient levels are generally lower at the surface of the sea because they are consumed faster than they are replaced.

Adsorption

Adsorption: When ions adhere to the surface of another kind of particle.
- The ions do not functionally react with the other ions.
- Clay particles are good at adsorption.

Vertical Profiles of Elements in Seawater

Conservative Elements
- Unchanged by biological processes.
- Their concentration is largely constant with depth.
Non-Conservative Elements
- Their concentration does change with depth, often showing a curve or profile.

Salt Sources/Sinks (Salt Cycles)

Salt comes from various sources and is removed through different sinks, influencing salinity.

Sources:
- Weathering and erosion of rocks (via river runoff, for example).
- Hydrothermal vents.
Sinks:
- Salt spray (removed from the ocean).
- Adsorption.
- Biological processes (e.g., organisms incorporating salts).

Nutrients and Decomposition

The concentration of nutrients in deeper water is typically higher.
- This is due to the decomposition and release of nutrients from biological material.
Redfield Ratio describes nutrient consumption and regeneration ratios, particularly for C:N:P (Carbon: Nitrogen: Phosphorus).
- When we know the molecular weight, we can calculate nutrients per ratio.
- For example, to find out how many grams of C result from the addition of 1g of P:
  $\frac{106 \text{ g C}}{1 \text{ g P}} \times \frac{1 \text{ g P}}{1} = 106 \text{ g C}$

Gases in Seawater

Nitrogen N2 and Oxygen O2 are the most abundant gases in seawater.
The concentrations of all three gases (likely referring to O2, CO2CO2, and N2N2
vary spatially and temporally.
- They are affected by both biological and physical processes.
These gases are considered non-conservative constituents because their concentrations are influenced by multiple processes.

Saturation Concentration of Gases

The saturation concentration refers to the maximum amount of a gas that can be held in solution within water.
The solubility of gases changes with:
- Temperature: $\downarrow$ Temp = $\uparrow$ gas solubility
- Salinity: $\downarrow$ Salinity = $\uparrow$ gas solubility
- Pressure: $\uparrow$ Pressure = $\uparrow$ gas solubility
Overall, colder and less-salty (fresher) water can hold more dissolved gas.