# Oceanography

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Category: Science
Slides: 32
Updated: 2026-05-17T20:49:36.924Z
Tags: science, oceanography

## Summary

Exploring Earth's Last Frontier: The Science of Our Oceans Key sections include: Oceanography; Table of Contents; What Is Oceanography?; History of Ocean Exploration; Ocean Basins & Bathymetry; Plate Tectonics & the Seafloor; Seawater Chemistry; Temperature & Salinity; Ocean Circulation: Surface Currents; Thermohaline Circulation.

## Slide Outline

1. Oceanography
2. Table of Contents
3. What Is Oceanography?
4. History of Ocean Exploration
5. Ocean Basins & Bathymetry
6. Plate Tectonics & the Seafloor
7. Seawater Chemistry
8. Temperature & Salinity
9. Ocean Circulation: Surface Currents
10. Thermohaline Circulation
11. Waves
12. Tides
13. Coastal Processes
14. Marine Sediments
15. The Ocean Carbon Cycle
16. Marine Ecosystems
17. The Deep Sea
18. Hydrothermal Vents
19. Coral Reefs
20. Phytoplankton & Ocean Productivity
21. Marine Food Webs
22. Fisheries Science
23. Ocean & Climate
24. El Nino & Climate Oscillations
25. Sea Level Rise
26. Ocean Acidification
27. Pollution & Plastics
28. Polar Oceans
29. Ocean Technology
30. Marine Policy & Law of the Sea
31. Future of the Ocean
32. Further Reading

## Slide Transcript

### Slide 1: Oceanography

- Exploring Earth's Last Frontier: The Science of Our Oceans
- The ocean covers 71% of Earth's surface, drives our climate, hosts most of life's biodiversity, and remains less explored than the surface of Mars.
- 1 / 32

### Slide 2: Table of Contents

- 01 What Is Oceanography?
- 02 History of Ocean Exploration
- 03 Ocean Basins & Bathymetry
- 04 Plate Tectonics & the Seafloor
- 05 Seawater Chemistry
- 06 Temperature & Salinity
- 07 Ocean Circulation
- 08 Thermohaline Circulation
- 09 Waves
- 10 Tides
- 11 Coastal Processes
- 12 Marine Sediments
- 13 The Carbon Cycle
- 14 Marine Ecosystems
- 15 The Deep Sea
- 16 Hydrothermal Vents
- 17 Coral Reefs
- 18 Phytoplankton & Productivity
- 19 Marine Food Webs
- 20 Fisheries Science
- 21 Ocean & Climate
- 22 El Nino & Oscillations
- 23 Sea Level Rise
- 24 Ocean Acidification
- 25 Pollution & Plastics
- 26 Polar Oceans
- 27 Ocean Technology
- 28 Marine Policy & Law
- 29 Future of the Ocean
- 30 Further Reading
- 2 / 32

### Slide 3: What Is Oceanography?

- Oceanography is the interdisciplinary science of the ocean, encompassing its physics, chemistry, biology, and geology. It studies everything from surface waves to abyssal trenches, from microscopic plankton to planet-scale currents.
- The Four Pillars
- Physical Oceanography: Currents, waves, tides, temperature, mixing
- Chemical Oceanography: Seawater composition, cycles, gases, pH
- Biological Oceanography: Marine life, ecosystems, productivity
- Geological Oceanography: Seafloor, sediments, tectonics, coastlines
- Why It Matters
- Ocean absorbs 93% of excess heat from greenhouse warming
- Produces over 50% of Earth's oxygen (phytoplankton)
- 3 billion people depend on ocean for primary protein source
- Global shipping moves 80% of trade by tonnage
- Regulates weather and climate for entire planet
- 71%
- Earth's surface
- 1.335B
- km3 of water
- 3,688m
- Average depth
- ~20%
- Seafloor mapped in detail
- 3 / 32

### Slide 4: History of Ocean Exploration

- From Polynesian voyagers navigating by stars to robotic submersibles mapping the abyss, humanity's understanding of the ocean has expanded dramatically over millennia.
- ~3000 BCEPolynesian navigation across Pacific using stars, swells, and bird behavior
- 325 BCEPytheas of Massalia describes tides' relationship to the Moon
- 1405-1433Zheng He's treasure fleet explores Indian Ocean with 300+ ships
- 1768-1779Captain Cook's voyages: first systematic ocean temperature measurements
- 1872-1876HMS Challenger expedition: founding of modern oceanography (4,700+ species discovered)
- 1960Trieste bathyscaphe reaches Challenger Deep (10,916m) -- Piccard and Walsh
- 1977Discovery of hydrothermal vents and chemosynthetic life on Galapagos Rift
- 2010s-presentArgo float network (4,000+ autonomous profilers), satellite altimetry, autonomous underwater vehicles
- 4 / 32

### Slide 5: Ocean Basins & Bathymetry

- The world ocean is divided into five major basins, each with distinct characteristics. The seafloor topography is as varied as any continental landscape, with mountains, plains, trenches, and ridges.
- OceanArea (M km2)Avg Depth (m)Max Depth (m)
- Pacific165.254,28010,935 (Mariana Trench)
- Atlantic106.463,6468,376 (Puerto Rico Trench)
- Indian70.563,7417,258 (Java Trench)
- Southern21.963,2707,235 (South Sandwich Trench)
- Arctic14.061,2055,450 (Molloy Deep)
- Major Seafloor Features
- Continental shelf: shallow extension of continents (0-200m)
- Continental slope: steep descent to deep ocean
- Abyssal plain: flat deep seafloor (3,000-6,000m)
- Mid-ocean ridges: 65,000 km volcanic mountain chain
- Trenches: subduction zones, deepest features on Earth
- Seamounts & Islands
- Over 100,000 seamounts estimated (most unmapped)
- Hotspot volcanism creates island chains (Hawaii, Galapagos)
- Guyots: flat-topped seamounts eroded at sea level, then submerged
- Atolls: coral reefs growing on subsiding volcanic islands (Darwin's theory)
- 5 / 32

### Slide 6: Plate Tectonics & the Seafloor

- The ocean floor is geologically young (
- Seafloor Spreading
- Mid-ocean ridges produce new basaltic crust at 2-15 cm/year
- Magnetic striping: alternating polarity reversals recorded in rock
- Proved continental drift and plate tectonics (1960s revolution)
- Youngest crust at ridge axis; oldest at continental margins
- Atlantic widening ~2.5 cm/year; Pacific shrinking
- Subduction Zones
- Oceanic crust dives beneath continental or other oceanic plates
- Creates deep trenches (Mariana: 10,935m)
- Generates major earthquakes and tsunamis (2004, 2011)
- Volcanic arcs form above (Ring of Fire: 75% of world's volcanoes)
- Recycles water and carbon back into mantle
- The Wilson Cycle: Oceans are born (rifting), grow (spreading), shrink (subduction), and close (continental collision). The Atlantic is young and growing; the Pacific is ancient and shrinking.
- 6 / 32

### Slide 7: Seawater Chemistry

- Seawater is a complex solution of dissolved salts, gases, nutrients, and organic compounds. Its chemistry controls ocean biology, climate interactions, and geochemical cycles operating over millions of years.
- Major Dissolved Ions
- Iong/kg% of salts
- Chloride (Cl-)19.455.0%
- Sodium (Na+)10.830.6%
- Sulfate (SO4 2-)2.77.7%
- Magnesium (Mg2+)1.33.7%
- Calcium (Ca2+)0.411.2%
- Potassium (K+)0.401.1%
- Key Properties
- Salinity: ~35 g/kg (35 psu) on average
- Principle of constant proportions: ion ratios nearly uniform everywhere
- Residence time: how long an element stays (Na: 260M years; Al: 100 years)
- Dissolved gases: O2 (surface), CO2 (drives pH), N2 (inert)
- Nutrients: nitrate, phosphate, silicate -- limit biological production
- 7 / 32

### Slide 8: Temperature & Salinity

- Temperature and salinity are the two master variables of physical oceanography. Together they determine seawater density, which drives the global circulation that distributes heat around the planet.
- Ocean Temperature Structure
- Surface layer: warm, well-mixed by wind (0-200m)
- Thermocline: rapid temperature decrease with depth (200-1000m)
- Deep ocean: cold (1-4C everywhere), uniform, slow-moving
- Surface ranges from -1.8C (polar) to 30C+ (tropics)
- Average ocean temperature: ~3.5C (the ocean is mostly cold and dark)
- Salinity Patterns
- Highest in subtropics (high evaporation, low rain): 36-37 psu
- Lower at equator (high rainfall) and poles (ice melt): 33-34 psu
- Mediterranean: 38-39 psu (enclosed, high evaporation)
- Baltic Sea: 6-8 psu (river input, enclosed)
- Red Sea: up to 41 psu (hottest enclosed sea)
- T-S Diagrams: By plotting temperature vs. salinity, oceanographers can identify and track water masses as they move through the ocean. Each water mass has a distinctive T-S signature from its formation region.
- 8 / 32

### Slide 9: Ocean Circulation: Surface Currents

- Surface currents are driven by wind and deflected by the Coriolis effect (Earth's rotation), forming large gyres that circulate clockwise in the Northern Hemisphere and counterclockwise in the Southern.
- Major Current Systems
- Gulf Stream: Transports 30 Sv (30 million m3/s) -- warms NW Europe
- Kuroshio: Pacific equivalent; warms Japan
- Antarctic Circumpolar Current: Largest current (130 Sv); circles Antarctica unimpeded by land
- Equatorial currents: Westward flow driven by trade winds
- Upwelling zones: Cold, nutrient-rich water surfaces (Peru, California, Benguela)
- Driving Forces
- Wind stress: Primary driver of surface currents
- Coriolis effect: Deflects motion right (NH) or left (SH)
- Ekman transport: Net water movement 90 degrees from wind
- Western boundary intensification: Why western currents (Gulf Stream) are faster and narrower
- Geostrophic balance: Pressure gradient balanced by Coriolis
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### Slide 10: Thermohaline Circulation

- The thermohaline circulation (THC) is the slow, deep ocean conveyor belt driven by density differences from temperature and salinity. It takes ~1,000 years for water to complete a full circuit and plays a critical role in distributing heat globally.
- How It Works
- Cold, salty water forms in North Atlantic (Norwegian/Greenland Seas) and around Antarctica
- Dense water sinks to the abyss (North Atlantic Deep Water, Antarctic Bottom Water)
- Deep water flows along ocean floor toward equator and other basins
- Gradual upwelling in Pacific and Indian Oceans returns water to surface
- Surface currents carry warm water back to formation regions
- Climate Significance
- Transports ~1.5 PW (petawatts) of heat northward in Atlantic
- Makes NW Europe 5-10C warmer than equivalent latitudes
- Slowdown evidence: AMOC has weakened ~15% since mid-20th century
- Past shutdowns caused abrupt climate shifts (Younger Dryas, 12,800 years ago)
- Climate models project 25-50% weakening by 2100 under high emissions
- 10 / 32

### Slide 11: Waves

- Ocean waves are energy traveling through water, generated primarily by wind. They range from tiny capillary ripples to massive swells that cross entire ocean basins, and their physics underpins coastal engineering, navigation, and renewable energy.
- Wave Properties
- Waves transmit energy, not water (water moves in circular orbits)
- Wave speed depends on wavelength in deep water: c = sqrt(gL/2pi)
- Waves "feel bottom" when depth Breaking occurs when wave height > 1/7 of wavelength
- Maximum observed wave: 29.1m (North Atlantic, 2000; buoy measurement)
- Wave Types
- Capillary waves: Wind waves (sea): locally generated, chaotic
- Swell: mature waves that have left generation area; organized
- Tsunamis: seismic sea waves; wavelength ~200 km, speed ~800 km/h
- Internal waves: oscillations within stratified water layers
- 11 / 32

### Slide 12: Tides

- Tides are the longest waves in the ocean, driven by the gravitational pull of the Moon and Sun. They profoundly affect coastal ecosystems, navigation, and are increasingly harnessed for energy.
- Tidal Forces
- Moon's gravity creates two tidal bulges (toward and away from Moon)
- Sun's contribution is ~46% of Moon's (farther but more massive)
- Spring tides: Moon + Sun aligned; maximum range
- Neap tides: Moon + Sun at 90 degrees; minimum range
- Tidal period: ~12h 25min (semidiurnal in most places)
- Tidal Ranges
- Open ocean: typically Bay of Fundy (Canada): up to 16m (world record)
- Bristol Channel (UK): up to 14m
- Mediterranean: nearly tideless (Resonance in bays and estuaries amplifies tidal range dramatically
- Tidal Energy: Total tidal energy dissipation is ~3.7 TW, mostly in shallow seas. This gradually slows Earth's rotation (days lengthen by ~2.3 ms/century) and pushes the Moon farther away (~3.8 cm/year).
- 12 / 32

### Slide 13: Coastal Processes

- Where ocean meets land, powerful forces reshape coastlines through erosion, sediment transport, and deposition. Coasts are among the most dynamic environments on Earth, changing on timescales from seconds to millennia.
- Erosion
- Wave energy focuses on headlands. Hydraulic action, abrasion, and chemical weathering carve cliffs, sea caves, arches, and stacks. Retreat rates: 0.1 to 10+ m/year depending on rock type.
- Sediment Transport
- Longshore drift moves sediment parallel to coast. River inputs, cliff erosion, and biological production supply material. Sand budgets: input vs. loss determines beach health.
- Depositional Features
- Beaches, barrier islands, spits, tombolos, deltas. The US East Coast's barrier islands protect mainland from storms. Deltas form where rivers dump sediment faster than waves remove it.
- Human Impact
- 40% of world population lives within 100 km of coast
- Seawalls and groins disrupt natural sediment flow
- Dam construction starves coasts of river sediment
- Sand mining for construction depletes beaches globally
- Storm Surges
- Low atmospheric pressure + onshore wind raises sea level
- Hurricane Katrina (2005): 8.5m surge
- Typhoon Haiyan (2013): 7m+ surge in Philippines
- Climate change: larger surges atop higher baseline sea level
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### Slide 14: Marine Sediments

- The ocean floor is blanketed by sediment that records Earth's history like pages in a book. Seafloor cores provide records of climate, volcanic activity, evolution, and ocean chemistry spanning millions of years.
- Sediment Types
- Terrigenous: Land-derived (clay, silt, sand); thickest near continents
- Biogenous: Shells and skeletons of plankton (calcareous and siliceous oozes)
- Hydrogenous: Precipitated from seawater (manganese nodules, evaporites)
- Cosmogenous: Extraterrestrial material (micrometeorites, cosmic dust)
- What Sediments Tell Us
- Oxygen isotopes in foraminifera shells: past temperature and ice volume
- Species assemblages: past ocean productivity and circulation
- Volcanic ash layers: eruption chronology
- Iridium anomaly at K-Pg boundary: asteroid impact evidence
- Accumulation rates: 1-10 cm per 1,000 years (deep ocean)
- 14 / 32

### Slide 15: The Ocean Carbon Cycle

- The ocean is the largest active carbon reservoir on Earth, holding ~38,000 Gt C compared to ~870 Gt in the atmosphere. It absorbs ~25% of human CO2 emissions annually, acting as a critical climate buffer.
- Solubility Pump
- CO2 dissolves more readily in cold water. Cold polar surface waters absorb CO2, sink, and carry it to depth. This physical process accounts for most ocean carbon uptake.
- Biological Pump
- Phytoplankton fix CO2 through photosynthesis. Dead organisms and fecal pellets sink, transporting carbon to deep ocean. Only ~1% of surface production reaches the seafloor.
- Carbonate Pump
- Organisms build calcium carbonate shells (CaCO3). When shells sink below the carbonate compensation depth (~4,500m), they dissolve. Above it, they accumulate as sediment.
- ~2.5
- Gt C absorbed/year
- 38,000
- Gt C in ocean
- ~50
- Gt C surface production/year
- 25%
- of human CO2 absorbed
- 15 / 32

### Slide 16: Marine Ecosystems

- The ocean hosts an extraordinary diversity of ecosystems, from sunlit surface waters to the permanent darkness of the abyss. Marine life has adapted to every conceivable ocean environment.
- Pelagic (Open Water)
- Divided by depth: epipelagic (0-200m, sunlit), mesopelagic (200-1000m, twilight), bathypelagic (1000-4000m, midnight), abyssopelagic (4000-6000m), hadopelagic (trenches).
- Benthic (Seafloor)
- From intertidal to hadal zones. Includes kelp forests, seagrass meadows, cold-water corals, abyssal plains, and chemosynthetic vent communities.
- Coastal
- Highest productivity zones: estuaries, mangroves, salt marshes, coral reefs, rocky shores. Where terrestrial nutrients meet marine systems.
- Marine Biodiversity: The ocean contains representatives of 34 of 36 known animal phyla (land has only 17). Estimated 0.7-1 million marine eukaryotic species, with perhaps 2/3 still undescribed. New species are discovered at a rate of ~2,000/year.
- 16 / 32

### Slide 17: The Deep Sea

- Below 1,000 meters lies the largest habitat on Earth: the deep sea. It is cold (1-4C), dark, under enormous pressure, and was long thought lifeless. We now know it hosts diverse, uniquely adapted communities.
- Conditions
- No sunlight: complete darkness below ~1,000m
- Pressure: increases 1 atm per 10m (1,100 atm at Mariana Trench)
- Temperature: 1-4C (constant, no seasons)
- Food-limited: depends on "marine snow" from surface
- Slow-motion world: metabolic rates orders of magnitude lower than surface
- Deep-Sea Adaptations
- Bioluminescence: 76% of deep-sea organisms produce light
- Gigantism: some deep-sea species grow much larger than shallow relatives
- Extreme pressure tolerance: piezophilic enzymes and flexible membranes
- Ultra-slow growth: some deep corals are 4,000+ years old
- Enormous mouths and expandable stomachs for rare feeding opportunities
- 17 / 32

### Slide 18: Hydrothermal Vents

- Discovered in 1977, hydrothermal vents are among the most extraordinary environments on Earth. Superheated, mineral-rich water erupts from the seafloor, supporting lush ecosystems based entirely on chemical energy rather than sunlight.
- The System
- Seawater percolates through crust, heated by magma to 350-400C
- Dissolves metals and sulfides from rock
- Erupts as "black smokers" (metal sulfide particles) or "white smokers"
- Found along mid-ocean ridges, back-arc basins, hotspots
- Over 700 vent fields discovered globally
- Vent Life
- Chemosynthetic bacteria: use H2S oxidation for energy (not sunlight)
- Giant tube worms (Riftia): up to 2m; harbor symbiotic bacteria in trophosome
- Vent shrimp, crabs, mussels, clams with bacterial symbionts
- Pompeii worm: survives 80C -- most heat-tolerant animal
- Possible origin of life? (hot, chemical energy, mineral catalysts)
- "The discovery of deep-sea hydrothermal vents was one of the great scientific revelations of the 20th century -- life thriving in total darkness on chemical energy alone." -- Robert Ballard
- 18 / 32

### Slide 19: Coral Reefs

- Coral reefs are the most biodiverse marine ecosystems, supporting ~25% of all marine species while covering less than 0.1% of the ocean floor. Built by tiny coral polyps over millennia, they face existential threats from warming and acidification.
- 25%
- of marine species
- 500M
- people dependent
- $375B
- annual economic value
- 50%
- lost since 1950s
- How Reefs Work
- Coral polyps secrete calcium carbonate skeletons
- Symbiotic zooxanthellae algae provide 90% of coral's energy via photosynthesis
- Requires warm (20-30C), clear, shallow water
- Framework creates habitat for thousands of species
- Grows 1-10 cm/year vertically; reefs are thousands of years old
- Threats
- Bleaching: Heat stress expels zooxanthellae; coral starves (1C above normal triggers it)
- Ocean acidification: Lower pH dissolves carbonate; harder to build skeleton
- Overfishing: Removes grazers; algae overgrow coral
- Pollution: Nutrient runoff, sediment, chemicals
- 70-90% of reefs projected lost at 1.5C warming; nearly all at 2C
- 19 / 32

### Slide 20: Phytoplankton & Ocean Productivity

- Microscopic photosynthetic organisms -- phytoplankton -- form the base of nearly all marine food webs and produce roughly half of Earth's oxygen. Their distribution is controlled by light, nutrients, and mixing.
- Major Groups
- Diatoms: Silica shells; dominate productive waters; major carbon exporters
- Coccolithophores: Calcium carbonate plates; create white "blooms" visible from space
- Dinoflagellates: Many toxic species; cause "red tides"
- Cyanobacteria: Prochlorococcus -- most abundant phototroph on Earth (3 x 10^27 cells)
- Green algae, silicoflagellates, cryptophytes
- Productivity Patterns
- Highest near coasts (upwelling, nutrients) and at high latitudes (spring blooms)
- Open ocean gyres are "deserts" -- nutrient-depleted surface
- Total marine net primary production: ~50 Gt C/year
- Iron limitation in "HNLC" regions (Southern Ocean, subarctic Pacific)
- Seasonal cycles driven by light + nutrient mixing dynamics
- 20 / 32

### Slide 21: Marine Food Webs

- Marine food webs are complex networks connecting microscopic producers to apex predators. Energy transfers through trophic levels with roughly 10% efficiency at each step, structuring the abundance of marine life.
- Trophic Structure
- Primary producers: Phytoplankton, seaweeds, seagrasses
- Primary consumers: Zooplankton, herbivorous fish, filter feeders
- Secondary consumers: Small predatory fish, squid, jellyfish
- Tertiary consumers: Tuna, sharks, marine mammals
- Apex predators: Orcas, great white sharks, sperm whales
- Key Concepts
- Microbial loop: Bacteria recycle dissolved organic matter; adds trophic complexity
- Trophic cascade: Removing predators triggers chain reaction through food web
- Bioaccumulation: Toxins concentrate up food chain (mercury in tuna)
- Whale pump: Whales fertilize surface with nutrients from deep dives
- Diel vertical migration: Largest animal migration on Earth -- daily
- 21 / 32

### Slide 22: Fisheries Science

- Fisheries science aims to understand fish populations and set sustainable harvest levels. Despite advances in stock assessment, roughly 34% of global fish stocks are overfished, with major consequences for marine ecosystems and human food security.
- Key Concepts
- Maximum Sustainable Yield (MSY): Largest catch maintainable indefinitely
- Stock-recruitment relationships: How many adults produce enough juveniles
- Bycatch: Unintended species caught (40% of global catch)
- Trawling impact: Bottom trawling disturbs area equivalent to half of continental shelves annually
- IUU fishing: Illegal, unreported, unregulated -- $23 billion/year
- State of Fisheries
- Global marine catch: ~80 million tonnes/year (plateaued since 1990s)
- 34% of stocks overfished, 60% fished at maximum
- Only 6% underfished (room to grow)
- Aquaculture now produces more fish than wild catch globally
- Marine protected areas show rapid fish recovery (400%+ biomass increase)
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### Slide 23: Ocean & Climate

- The ocean is the flywheel of the climate system. Its enormous heat capacity, circulation patterns, and biogeochemical cycles moderate temperature extremes, redistribute heat, and regulate atmospheric CO2 on timescales from years to millennia.
- Heat Storage
- Ocean has absorbed 93% of excess heat from global warming since 1970
- Top 2000m has warmed by ~0.09C since 1955 (enormous thermal energy)
- Equivalent to 3.6 x 10^23 joules absorbed -- like 5 Hiroshima bombs per second
- This thermal inertia means warming continues even if emissions stop
- "Committed warming" -- ocean slowly releases stored heat to atmosphere
- Climate Regulation
- Evaporation fuels weather systems (hurricanes powered by warm ocean)
- CO2 absorption buffers atmospheric concentration
- Albedo feedback: loss of sea ice exposes dark water, absorbs more heat
- Coastal upwelling drives fog and cool temperatures (San Francisco)
- Ocean-atmosphere coupling drives major climate modes (ENSO, NAO, PDO)
- 23 / 32

### Slide 24: El Nino & Climate Oscillations

- El Nino-Southern Oscillation (ENSO) is the strongest year-to-year climate fluctuation on Earth, affecting weather patterns globally. It exemplifies how ocean-atmosphere coupling creates powerful climate variability.
- ENSO Phases
- El Nino: Warm water shifts east across Pacific; trade winds weaken. Drought in Australia/Indonesia, floods in Americas.
- La Nina: Enhanced trade winds pile warm water west; cold upwelling strengthens in east Pacific. Opposite weather impacts.
- Neutral: Normal conditions; trade winds push warm water westward.
- Cycle: irregular, 2-7 year period
- 2023-24 El Nino contributed to record global temperatures
- Other Oscillations
- NAO: North Atlantic Oscillation -- European winter weather
- PDO: Pacific Decadal Oscillation -- 20-30 year cycles
- AMO: Atlantic Multidecadal Oscillation -- hurricane activity
- IOD: Indian Ocean Dipole -- Australian/African rainfall
- These interact with and modulate anthropogenic warming
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### Slide 25: Sea Level Rise

- Global mean sea level has risen ~21 cm since 1900 and is accelerating. By 2100, projections range from 0.3m to over 1m depending on emissions, with multi-meter rise possible over centuries from ice sheet collapse.
- Causes
- Thermal expansion: Warmer water expands (~40% of observed rise)
- Glaciers melting: Mountain glaciers worldwide (~30%)
- Greenland ice sheet: Accelerating mass loss (~20%)
- Antarctic ice sheet: Increasingly unstable, especially West Antarctica (~10%)
- Current rate: ~3.6 mm/year (doubled since 1993)
- Impacts
- Coastal flooding affects 1 billion people in low-elevation zones
- Small island nations face existential threat (Tuvalu, Maldives, Marshall Islands)
- Saltwater intrusion into groundwater aquifers
- Wetland and beach loss (cannot migrate inland in developed areas)
- Storm surge amplification: even small SLR greatly increases flood frequency
- Ice Sheet Tipping Points: If warming crosses certain thresholds, ice sheet loss becomes self-sustaining (marine ice cliff instability). West Antarctic Ice Sheet collapse alone would raise sea level ~3.3m over centuries.
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### Slide 26: Ocean Acidification

- As the ocean absorbs CO2, carbonic acid forms, lowering pH. Ocean pH has dropped 0.1 units since pre-industrial times (26% increase in acidity). This "other CO2 problem" threatens calcifying organisms and marine food webs.
- The Chemistry
- CO2 + H2O -> H2CO3 -> H+ + HCO3- -> 2H+ + CO3 2-
- More CO2 = more H+ ions = lower pH
- Also reduces carbonate ion (CO3 2-) concentration
- Pre-industrial pH: ~8.2; Current: ~8.1; Projected 2100: ~7.8
- Fastest pH change in at least 300 million years
- Biological Impacts
- Corals: harder to build skeletons; dissolution in extreme scenarios
- Pteropods (sea butterflies): shell thinning observed in Southern Ocean
- Oysters, mussels: larval development impaired
- Fish: behavioral changes, impaired sensory function in some species
- Ecosystem cascades: base of food web affected, propagates upward
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### Slide 27: Pollution & Plastics

- Human activities introduce vast quantities of pollutants into the ocean: plastics, chemicals, nutrients, oil, noise, and light. Plastic pollution has become emblematic of ocean degradation, with an estimated 8 million tonnes entering annually.
- Plastic Crisis
- 171 trillion plastic particles floating in surface ocean
- Microplastics (Great Pacific Garbage Patch: 1.6 million km2 (3x France)
- Ingested by 700+ marine species
- Takes 500+ years to degrade; breaks into smaller pieces, never disappears
- Other Pollutants
- Nutrient pollution (nitrogen, phosphorus): creates dead zones (500+ globally)
- Oil spills: Deepwater Horizon released 4.9 million barrels (2010)
- Heavy metals: mercury bioaccumulates in tuna, swordfish
- Persistent organic pollutants (PCBs, DDT): still found decades after ban
- Pharmaceutical residues: endocrine disruptors in coastal waters
- Ocean Noise
- Shipping doubled low-frequency noise every decade since 1960
- Seismic surveys: 250+ dB pulses every 10 seconds for weeks
- Whales, dolphins rely on sound -- noise causes stress, strandings
- Fish deterred from feeding and spawning grounds
- Some regulations emerging (speed limits, routing)
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### Slide 28: Polar Oceans

- The Arctic and Southern Oceans are warming faster than any other marine regions, with profound consequences for sea ice, global circulation, and unique polar ecosystems adapted to extreme cold.
- Arctic Ocean
- Summer sea ice: declined ~40% since satellite era (1979)
- Ice-free summer possible by 2040s-2050s
- Opening Northern Sea Route and Northwest Passage to shipping
- Permafrost thaw releasing methane from seabed
- Polar bears, walrus, ice-dependent seals losing habitat
- Southern Ocean
- Encircles Antarctica; strongest current on Earth (ACC: 130 Sv)
- Forms Antarctic Bottom Water -- drives global deep circulation
- Krill: keystone species (500 million tonnes); base of Antarctic food web
- West Antarctic ice shelves thinning; risk of marine ice sheet instability
- Most productive whale feeding grounds (recovering post-whaling)
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### Slide 29: Ocean Technology

- Oceanography has been transformed by technology -- from crude lead-line soundings to autonomous robots, satellite remote sensing, and genomic sampling. Modern tools reveal the ocean at unprecedented resolution.
- Autonomous Systems
- Argo floats (4,000+): profile temperature and salinity to 2,000m every 10 days. Gliders traverse basins for months. AUVs map seafloor and sample biology at depth.
- Satellites
- Altimetry measures sea level to mm precision. Sea surface temperature from infrared sensors. Ocean color reveals chlorophyll and productivity. Gravity satellites detect deep ocean mass changes.
- Submersibles & ROVs
- Alvin (4,500m): the workhorse since 1964. ROV Jason: remotely operated to 6,500m. Full-ocean-depth vehicles: Limiting Factor, Fendouzhe (11,000m class).
- Genomics
- Environmental DNA (eDNA): detect species from water samples. Metagenomics revealed millions of unknown ocean genes. Tara Oceans expedition sequenced global marine microbiome.
- Modeling
- Ocean general circulation models (OGCMs) simulate global ocean at 10 km resolution. Coupled to atmospheric models for climate projections. Ecosystem models predict fisheries.
- Acoustic Methods
- Multibeam sonar maps seafloor topography. SOFAR channel: sound travels thousands of km (used for float tracking). Acoustic tomography measures ocean temperature changes.
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### Slide 30: Marine Policy & Law of the Sea

- The ocean is governed by a complex framework of international law, most importantly the UN Convention on the Law of the Sea (UNCLOS, 1982), which defines maritime zones and responsibilities.
- Maritime Zones
- Territorial Sea: 0-12 nautical miles (full sovereignty)
- Contiguous Zone: 12-24 nm (customs, immigration enforcement)
- Exclusive Economic Zone: 0-200 nm (resource rights)
- Continental Shelf: Up to 350 nm (seabed resources)
- High Seas: Beyond EEZ -- common heritage of mankind
- Key Agreements
- UNCLOS (1982): "Constitution for the oceans" -- ratified by 168 countries
- BBNJ Treaty (2023): Biodiversity beyond national jurisdiction -- new MPAs on high seas
- Global Ocean Treaty goal: 30% of ocean protected by 2030 ("30x30")
- MARPOL: Prevention of pollution from ships
- IWC: International Whaling Commission moratorium (1986)
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### Slide 31: Future of the Ocean

- The ocean faces unprecedented pressures but also unprecedented attention. The UN Decade of Ocean Science for Sustainable Development (2021-2030) represents growing recognition that ocean health is inseparable from human wellbeing.
- Challenges
- Warming: +1.5 to 4C surface temperature by 2100 depending on emissions
- Deoxygenation: ocean has lost 2% of O2 since 1960; expanding dead zones
- Deep-sea mining: threatens unique ecosystems for polymetallic nodules
- Overfishing continues despite scientific advice
- Cumulative stressors: warming + acidification + pollution interact
- Opportunities
- Marine protected areas work: rapid ecosystem recovery when enforced
- Offshore renewable energy: wind, tidal, wave, OTEC
- Blue carbon: mangroves, seagrass, kelp store 5x more carbon than forests per area
- Sustainable aquaculture can reduce pressure on wild stocks
- Ocean-based carbon dioxide removal research expanding
- "We know more about the surface of Mars than we do about the deep sea floor. The ocean is our planet's last great frontier of discovery." -- Sylvia Earle
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### Slide 32: Further Reading

- Textbooks
- Essentials of Oceanography -- Trujillo & Thurman (accessible introduction)
- Introduction to Physical Oceanography -- Knauss (circulation and dynamics)
- Biological Oceanography -- Miller & Wheeler
- Marine Chemistry -- Millero (chemical oceanography)
- Ocean Circulation and Climate -- Siedler et al. (advanced)
- Popular & Current
- The World Is Blue -- Sylvia Earle (exploration and conservation)
- The Brilliant Abyss -- Helen Scales (deep-sea wonders)
- The Underworld -- Susan Casey (deep ocean exploration)
- Oceans -- BBC/David Attenborough documentary series
- The Ocean Portal -- Smithsonian (free online resource)
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