Final Oceanography Prelim 2

Primary Production

Rate at which phytoplankton convert CO₂ into organic matter through photosynthesis; base of the marine food web.

Compensation Light Level

Light intensity where photosynthetic CO₂ uptake exactly equals respiratory CO₂ loss; Net Primary Production = 0.

Compensation Depth

Depth where light equals the compensation light level; below this depth, phytoplankton lose more carbon than they gain.

Critical Depth Theory

When mixed layer depth < critical depth, phytoplankton stay long enough in light for growth to exceed respiration → spring bloom forms.

Mixing Depth

Depth to which surface waters are mixed by wind; affects average light exposure of phytoplankton.

Light Limitation

Growth limited by insufficient light (deep water or winter).

Light Saturation

Optimal light for photosynthesis; further increases don’t increase growth.

Photoinhibition

Too-intense light damages photosynthetic machinery, reducing productivity.

Four Key Nutrients

Nitrogen (N), Phosphorus (P), Silica (Si), Iron (Fe).

Nutrient Limitation

When one essential nutrient is in short supply and restricts phytoplankton growth.

Main Source of N, P, Si

Vertical mixing or upwelling of nutrient-rich deep water.

Iron Source

Dust blown off continents; areas with little dust (e.g., Southern Ocean) are iron-limited.

Nitrogen Fixation

Process by which certain bacteria convert N₂ gas into usable nitrogen compounds; promoted by high iron input.

Phosphate Limitation

Occurs where iron input is extremely high (e.g., near dusty regions).

Subtropical Gyres

Low year-round production; warm, nutrient-poor water capped by strong stratification and Ekman convergence.

Equatorial Upwelling

High productivity where Trade Winds cause divergence and bring nutrient-rich water to the surface (especially eastern Pacific).

Coastal Upwelling

Seasonal winds drive offshore Ekman transport, pulling deep, nutrient-rich water upward → high seasonal productivity.

Tidal Mixing

Vertical mixing on shallow continental shelves that brings bottom nutrients to the surface; steady year-round.

Global NPP Split

~54% land, ~46% ocean; ocean production equal in magnitude to land.

Open Ocean Productivity

Low per square meter, but huge total due to vast area (~70% of ocean NPP).

Coastal Productivity

High per square meter but small total area; supports most fisheries.

Autotroph

Organism containing chlorophyll that produces its own food by photosynthesis.

Heterotroph

Organism lacking chlorophyll that consumes organic matter for energy.

Trophic Level

Position in a food chain based on what the organism eats and who eats it.

Size-Structured Web

Prey are ~1/10 the size of their predators; predator size increases by factor of 10 at each trophic level.

Exploitation Efficiency

Efficiency of finding, capturing, and ingesting prey (10–90%).

Gross Production Efficiency

Efficiency of converting ingested food into new biomass (20–60%).

Trophic Transfer Efficiency (TTE)

Overall transfer of energy between levels = Exploitation × Gross Production (~10%).

10% Rule

Only ~10% of energy or carbon passes to the next trophic level.

Diel Vertical Migration

Zooplankton migrate to surface at night to feed, descend during day to avoid visual predators.

Decoupling in Spring Bloom

North Atlantic copepods in diapause → low grazing → phytoplankton bloom unchecked → low exploitation efficiency.

Trophic Steps and Fish Yield

Shorter food chains (coastal upwelling) yield more harvestable fish than long food chains (open ocean).

Microbial Loop

Pathway where dissolved organic carbon from phytoplankton is used by heterotrophic bacteria, which are then eaten by protozoans → returns carbon to higher levels.

Epifluorescent Microscopy

Technique (1970s–1980s) revealing enormous bacterial abundance and distinguishing autotrophic vs. heterotrophic cells.

Analytical Flow Cytometry

1980s–1990s method that identified Prochlorococcus, a tiny chlorophyll-containing bacterium.

Prochlorococcus

Dominant autotroph in oligotrophic oceans; contributes ≥25% of global ocean primary production.

Efficient Biological Pump

Large phytoplankton → large grazers → large fecal pellets → sink quickly → carbon stored in deep ocean.

Inefficient Biological Pump

Small phytoplankton → small grazers → slow-sinking fecal matter → carbon respired back to CO₂ in surface waters.

Vertical Zonation

Species occur in distinct horizontal bands determined by tidal height.

Upper Limit (Intertidal)

Set by physical stress (desiccation, temperature, salinity, wave energy).

Lower Limit (Intertidal)

Set by biological interactions (competition, predation).

Intermediate Disturbance Hypothesis

Moderate disturbance maximizes diversity by preventing dominant species from monopolizing space.

Pisaster Starfish Experiment (Paine 1966)

Pisaster predation prevents mussel domination → increases species diversity.

Keystone Species

Species with impact on community structure disproportionate to its abundance (e.g., Pisaster).

Trophic Cascade

Changes at one trophic level cause alternating increases/decreases at others.

Sea Otter–Kelp Cascade

Sea otter ↓ → urchins ↑ → kelp ↓.

Sunflower Starfish–Kelp Cascade

Starfish disease ↓ → urchins ↑ → kelp ↓ (95% loss in NorCal).

Coral Anatomy

Animal polyp secreting calcium carbonate skeleton.

Zooxanthellae

Symbiotic algae living inside coral tissues; provide 60–90% of coral nutrition via photosynthesis.

Coral Bleaching

Loss of zooxanthellae due to stress (≥1°C above normal for weeks) → corals turn white and may die.

Coral Growth Rate

Very slow (1–20 mm per year).

Competition for Space

Corals compete with other corals and macroalgae for attachment sites.

Crown-of-Thorns Starfish

Major coral predator; outbreaks can devastate reefs.

Eutrophication

Nutrient runoff promotes macroalgae that overgrow corals.

Overfishing

Removes herbivorous fish → macroalgae unchecked → coral decline.

Ocean Acidification

Reduces coral calcification; makes reef building harder.

El Niño + Global Warming

Combined heat stress causes mass coral bleaching events (1998, 2015-16, 2023-24).

Coral Loss Stats

~50% of coral lost in last 150 years.

1.5 °C vs 2.0 °C Worlds

70–90% coral loss vs >99% loss (IPCC 2018).

Coral Tipping Point

Some scientists warn threshold may occur near 1.2 °C warming.

Pakicetus

Earliest known whale ancestor (~53 M yr ago); had diagnostic whale ear bone.

Air Bone (Auditory Bulla)

Unique ear structure linking ancient and modern whales.

Baleen Whales (Mysticetes)

Filter-feeders (no teeth); evolved ~35 M yr ago.

Toothed Whales (Odontocetes)

Use echolocation; have teeth.

Humpback, Gray, Right Whale Migration

Winter: warm low-latitudes (calving); Summer: high-latitudes (feeding).

Whale Songs (Mysticetes)

Long low-frequency sounds; mainly for sexual selection and possibly navigation.

Odontocete Clicks/Whistles

Short, high-frequency bursts for echolocation and communication.

Anthropogenic Noise Sources

(1) Naval sonar, (2) Commercial shipping, (3) Oil-exploration seismic air guns.

Commercial Shipping Noise

Degrades whale communication range; considered biggest population-level threat.

PCB Bioaccumulation

PCBs build up through food webs; top predators like orcas are most contaminated.

Whaling Moratorium

1985 global ban by International Whaling Commission (IWC).

Countries Evading Whaling Ban

Norway, Iceland, Japan.

Ethical Issues in Whaling

(1) Humane killing, (2) Whether hunted species are endangered or vulnerable.

Polar Nature of Water

Oxygen’s high electronegativity makes water molecules polar → excellent solvent for salts.

Hydrogen Bond

Weak electrostatic attraction between partial positive H and partial negative O on neighboring molecules.

Three Phases of Water

Solid (ice): max H-bonds, rigid lattice, Liquid: bonds continually break/reform, Gas: bonds broken, molecules independent

Specific Heat Capacity

Water’s is among the highest of any substance; slows ocean temperature change.

Latent Heat of Vaporization

Energy required to convert liquid to vapor; stores “hidden” heat in water vapor.

Evaporation

Removes heat from ocean (cools it); stores heat as latent heat in atmosphere.

Condensation

Releases latent heat to atmosphere when vapor turns to liquid.

High Heat Capacity Consequence

Ocean absorbs ~93% of excess planetary heat from greenhouse warming.

Salinity (‰ or PSU)

Grams of salt per 1000 g seawater; set by evaporation–precipitation balance at surface.

Hadley Circulation

Explains global patterns of precipitation, evaporation, and salinity (wet at 0° and 60°, dry at 30°).

Conservative Property

Unchanged once water leaves surface (e.g., salinity, temperature).

Non-Conservative Property

Changes below surface (e.g., nutrients, O₂, CO₂).

Geochemical Cycle

Movement of elements through sources, transformations, and sinks.

Dissolved Nutrient Profile

Low at surface (uptake by phytoplankton), high at depth (remineralization).

Conveyor-Belt Circulation

Deep-ocean current system transporting O₂-rich, nutrient-poor water from N. Atlantic to Pacific; picks up nutrients and CO₂ along the way.

Oxygen Minimum Zone (OMZ)

Depth where respiration consumes O₂ faster than replenishment.

Thermocline Strength & O₂

Stronger thermocline = less mixing → lower O₂; global warming enhances this.

Observed Ocean De-Oxygenation

~2% global decline since 1960 (some areas > 4%).

CO₂ Cycle in Ocean

Photosynthesis consumes CO₂ (surface sink), Respiration produces CO₂ (deep source), Exchange with atmosphere adds/removes CO₂, Deep-Ocean CO₂ Reservoir

Equatorial Upwelling CO₂ Flux

Brings CO₂-rich deep water to surface → net outgassing.

Southern Ocean CO₂ Flux

Major global sink for atmospheric CO₂.

Ocean Acidification

CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻ → H⁺ + CO₃²⁻; increases H⁺, lowers pH.

Extent of Acidification

Ocean absorbed ~30% of anthropogenic CO₂; surface acidity up 26% since Industrial Era.

Polar Seas Vulnerability

Cold water absorbs more CO₂; acidifies fastest.

Upwelling Regions

Already acidic deep water rises; further acidified by modern CO₂ levels.

Oyster Farm Impacts

West-coast hatcheries damaged by acidic upwelling waters; some moved to Hawaii.

Calcifying Organisms

Coccolithophores, pteropods, corals depend on CaCO₃; highly sensitive to acidification.