L2- Abiotic and Biotic Factors in Marine Ecosystems and Oceanography

Class Representatives Selection:
- The instructor finalized three students to serve as class representatives:
  - Callum: From Wolfspace (North).
  - Amelia: From the local area.
  - Daniel: From the East Side of Christchurch (Mount Pleasant area).
- Required Follow-up: Class representatives must email the instructor with their name, career path, main subject, and favorite sandwich (the instructor's favorite is "Marine").
- Communication: Photos of the representatives will be posted for the class to see.

Overview: Students were tasked with drawing a descriptive picture of the ocean to communicate their knowledge to a non-expert (e.g., parents).
Key Ocean Statistics:
- Oceans cover approximately $70\%$ of the Earth's surface.
- The average depth of the ocean is $4,000\,m$ .
Factors for Inclusion in the Drawing:
- Abiotic Factors: Water (salty), light penetration, temperature, oxygen ( $O_2$ ), $CO_2$ , nitrogen, currents, and salinity.
- Biotic Factors: Life (fish, whales, octopus, mollusks), kelp/seaweeds, and plankton.
- Geological Features: Continental shelf, land/sea interface, sea floor, trenches, mountains, and hydrothermal vents (e.g., white and black smokers).
- Physical Processes: Turbidity flows, upwelling (vertical movement), waves, and horizontal current movement.
- Stratification (Clines): Thermoclines (temperature), haloclines (salinity), and chemoclines (chemical composition).
- Human Impact: Pollution (marine debris like milk bottles or bags) and marine vessels (whaling boats).

Ecosystem Diversity: The ocean consists of diverse systems including reef systems (tropical and temperate), deep sea, subtidal, inshore, planktonic, and polar systems.
Aquatic Biome Categorization:
- Abyssal Zone: Regions deeper than $3,000\,m$ .
- Hadal Zone: The deepest sections of the ocean associated with tectonic trenches.
- Intertidal Zone: The area between high and low tide.
- Oceanic Pelagic: The open ocean water, distinct from inshore or reef systems.
Connectivity: Ocean biomes are not isolated; they interact deeply with land, the atmosphere, wind, and solar radiation.
Barriers to Movement: Speciation and unique biomes are created by land masses, temperature gradients, salinity differences, and underwater trenches.

Mid-Oceanic Ridge System:
- This is a continuous mountain range running $65,000\,km$ through the Pacific and Atlantic oceans.
- East Pacific Rise: Fast-expanding; spreads out quickly to form plateaus rather than steep peaks.
- Mid-Atlantic Ridge: Slowly spreading; forms steep peaks that can reach depths of $2,800\,m$ ( $8,200\,ft$ ) below the surface.
New Zealand Marine Geography:
- Often referred to as the "Eighth Continent" (Zealandia).
- The continental shelf averages $100\,km$ width around Canterbury but moves very close to shore in Kaikoura.
- Significant features include the Chatham Rise, the Tonga Trench, and the Kermadec Trench.

Regional Currents: Key currents around New Zealand include the Tasman Front, the East Cape Current (and associated eddies), the Antarctic Circumpolar Current, and the Subantarctic Front.
The Pacific Warm Pool:
- Located near Papua New Guinea; it is the world's largest reservoir of heat energy.
- Surface temperatures can reach up to $31^{\circ}C$ .
ENSO (El Ni\u00f1o Southern Oscillation):
- El Ni\u00f1o: The warm pool moves East toward South America. Impact in NZ: Stronger winds, wet West Coast, and dry East Coast.
- La Ni\u00f1a: The warm pool stays West. Impact in NZ: Dry West Coast and wet East Coast.
Marine Heatwaves: Defined based on how many days the sea surface temperature stays above the long-term average.

Solutes and Salinity:
- Sodium Chloride ( $NaCl$ ) accounts for $85\%$ of dissolved minerals.
- Sources: Chloride ( $Cl^-$ ) primarily comes from hydrothermal vents and volcanic activity. Sodium ( $Na^+$ ) comes from the weathering of terrestrial rocks.
- The Six Major Ions: Only six ions make up $99\%$ of the total composition of seawater (including Sodium, Chloride, Potassium, Magnesium, Sulfate).
Global Variations: Salinity varies based on the balance between evaporation (increases salinity) and freshwater input from rivers, rain, or melting snow (dilutes salinity).
The 1,000-Meter Stability: Salinity generally stabilizes at approximately $35\,\text{parts per thousand}$ at a depth of $1,000\,m$ .

Solar Radiation: $80\%$ of solar radiation is lost within the first $10\,m$ of depth.
Thermal Capacity: Water has a high thermal capacity due to hydrogen bonds, requiring significant "latent heat" to change temperature.
- Latent Heat of Melting: It takes $80\,calories$ to convert $0^{\circ}C$ ice to $0^{\circ}C$ water.
Density: Cold water is more dense and sinks; warm water is less dense. Seawater freezes at approximately $-2^{\circ}C$ due to its salt content.
Light Penetration:
- Long wavelengths (Red/Yellow) are absorbed in the first $5\,m$ .
- Blue light travels the deepest.
- Photosynthesis: Seaweeds and plankton primarily use blue, violet, and red light. They reflect green light, which is why they appear green. Some red seaweeds are found as deep as $150\,m$ ( $800\,ft$ ).

Solubility: Cold water can hold more dissolved oxygen ( $O_2$ ) than warm water. Poles generally have higher dissolved oxygen levels.
The Oxygen Minimum Zone (OMZ): Located below the photic zone. In this region, organic matter ("marine snow") falls and is decomposed by bacteria, which consume all the available oxygen.
The Thermohaline Circulation (Great Ocean Conveyor Belt):
- Cold, oxygen-rich water sinks at the North Atlantic poles.
- This water migrates deep for thousands of years, moving through the Atlantic to the Indian and eventually the Pacific Oceans.
- The Pacific has lower oxygen in its deep water compared to the Atlantic because the water has spent more time away from the surface, allowing fauna and bacteria to deplete its oxygen levels.
Nutrient Accumulation: While the surface is nutrient-poor because seaweeds and phytoplankton absorb minerals for growth, the deep ocean accumulates nutrients as organic matter falls and stays in the slow-moving conveyor belt.

Audience Question: "Is [the salinity] percentage like a rainfall average?"
- Response: Yes, it is based on differences from the rainfall average. For example, during La Ni\u00f1a, New Zealand sees higher rainfall (greener landscapes) than the brown, dry conditions typical of that time of year.
Audience Question: "When you say something is green, it's not absorbing [green light]?"
- Response: Correct. It is reflecting green light because it is not absorbing that specific wavelength; it is instead using the blue, violet, and red wavelengths for photosynthesis.
Student Interaction (Post-Lecture): An engineering student requested an override for a course conflict between their engineering classes and the marine biology labs.
- Response: The instructor agreed to override the conflict via email.