Temperate vs. Tropical Cyclones

1. Formation and Origin

Tropical Cyclones

• Form over warm tropical oceans between roughly 5° and 30° latitude (both hemispheres)
• Require sea surface temperatures (SST) above 26-27°C
• Need high atmospheric humidity, low vertical wind shear, and the Coriolis force to initiate rotation
• Energy source: latent heat released during condensation of moist, warm air rising from the ocean surface (warm-core thermal convection)
• Formation mechanism: convective instability - warm, humid air rises and releases heat, intensifying the low pressure below

Temperate (Extratropical) Cyclones

• Form in mid-latitudes (30°-65°), often along ocean-land boundaries or over land
• Energy source: baroclinic instability - the temperature contrast (and associated potential energy) between warm tropical and cold polar air masses
• Formation begins along the polar front, where cold polar air and warm tropical air meet
• The jet stream plays a key role in their development and steering
• Life cycle stages: initial wave → cyclogenesis → mature stage → occlusion → dissipation

2. Structure

3. Wind Speed and Location of Maximum Winds

• Tropical cyclones: Extremely high winds (120-250+ km/h), strongest in the lower troposphere near the boundary layer (just above the surface), decreasing with altitude
• Temperate cyclones: Moderate winds (typically 30-150 km/h), strongest winds found at the top of the troposphere in the core of the jet stream, increasing with height

4. Weather and Rainfall

5. Movement and Seasonality

• Tropical cyclones: Move westward initially (steered by trade winds), then curve poleward; slower movement; occur mainly in summer and early autumn when SSTs are highest
• Temperate cyclones: Move generally west to east (driven by the westerlies and jet stream); occur throughout the year but are most intense in winter when pole-to-equator temperature contrasts are greatest; in winter they take a more southerly track (e.g., across the Mediterranean), while in summer they move poleward

6. Decay

• Tropical cyclones weaken rapidly when they move over land (cut off from ocean heat) or cool water
• Temperate cyclones weaken through occlusion - the faster-moving cold front catches up to the warm front, lifting the warm air completely off the surface and cutting off the temperature contrast that drives the system; they can also transition into tropical cyclones under certain conditions (tropical transition)

7. Key Differences at a Glance

8. Regional Significance (Example: India)

• Tropical cyclones affect India's east coast (Bay of Bengal) and west coast (Arabian Sea) mainly in May-June and October-November. Examples: Cyclone Amphan (2020), Cyclone Biparjoy (2023)
• Temperate cyclones affect northern India as "Western Disturbances" in winter, bringing vital rain and snow to the Himalayas and northern plains - critical for rabi crops (wheat, mustard)

Temperature and Salinity of the Oceans

PART 1 - OCEAN TEMPERATURE

A. Heat Sources and Surface Temperature

B. Vertical Temperature Structure - Three Layers

1. Surface/Mixed Layer (0-200 m)

• Warmed directly by solar radiation
• Kept well-mixed by wind, waves, and surface currents
• Temperature is relatively uniform throughout this layer (hence "mixed layer")
• Depth varies: shallower in summer/tropics, deeper in winter/high latitudes

2. Thermocline (200-1,000 m)

• A zone of rapid temperature decrease with increasing depth
• Acts as a barrier between warm surface water and cold deep water
• Permanent thermocline: exists year-round in tropical and subtropical regions
• Seasonal thermocline: develops in spring/summer in mid-latitudes above the permanent thermocline, then breaks down in autumn/winter as storms mix the water
• Polar regions have NO thermocline - water is uniformly cold from surface to floor

3. Deep Ocean / Abyss (below ~1,000 m)

• Cold, dark, uniform temperatures of 0-3°C throughout most of the world's oceans
• Deep ocean water originates from cold, dense polar surface water that sinks (thermohaline circulation)
• Very little seasonal variation at these depths
• Makes up ~75% of the total ocean volume

C. Latitudinal Temperature Profiles (Summary)

• Tropical profile: Warm surface layer → sharp thermocline → cold deep water
• Mid-latitude profile: Moderately warm surface → seasonal thermocline above permanent thermocline → cold deep water
• Polar profile: Cold from surface to floor; no thermocline

D. Factors Affecting Ocean Temperature

1. Solar radiation (latitude and season)
2. Ocean currents - warm currents (e.g., Gulf Stream, Kuroshio) transport heat poleward; cold currents (e.g., Labrador, Benguela) cool coastal regions
3. Upwelling - brings cold deep water to the surface (e.g., off Peru, west Africa)
4. Depth - temperature drops rapidly below the mixed layer
5. Wind mixing - deepens the mixed layer
6. Land vs. ocean - continentality affects coastal sea temperatures

PART 2 - OCEAN SALINITY

A. What Is Salinity?

B. Factors That Increase Salinity

• Evaporation - removes fresh water, concentrates salts
• Sea ice formation - ice excludes salt when it freezes, increasing salinity of surrounding water ("brine rejection")
• Low precipitation

C. Factors That Decrease Salinity

• Precipitation (rain/snow) - adds fresh water
• River runoff - dilutes coastal waters
• Ice/glacier melting - adds fresh water
• High humidity / low evaporation

D. Latitudinal Variation of Salinity

E. Ocean Basin Differences

• Atlantic Ocean: saltiest of all major ocean basins (~35.5-37 ppt) due to high evaporation and export of atmospheric moisture to the Pacific
• North Pacific: freshest major ocean (~33-34 ppt) due to higher precipitation
• Mediterranean Sea: very high salinity (~38-39 ppt) due to extreme evaporation in an enclosed basin
• Red Sea/Persian Gulf: highest salinities (~40-42 ppt) - hot, arid, enclosed, minimal freshwater input
• Baltic Sea: very low salinity (~7-8 ppt) - semi-enclosed, massive river input, low evaporation

F. Vertical Salinity Structure - The Halocline

• Surface layer: variable, controlled by E-P balance, rivers, and ice
• Halocline: a zone of rapid salinity change with depth (analogous to the thermocline)
  • In tropical/subtropical regions: salinity generally decreases slightly with depth
  • At mid-depth (~1,000-2,000 m): outflows from the Mediterranean and Red Seas create a salinity maximum in the North Atlantic and Indian Ocean respectively
  • There is also a salinity minimum at intermediate depths (~1,000 m) in subtropical/tropical regions caused by relatively fresh subpolar water flowing in
• Deep ocean: fairly uniform salinity of ~34.5-35 ppt

PART 3 - TEMPERATURE, SALINITY, AND DENSITY (T-S Diagrams)

• Cold, salty water is densest and sinks to the ocean floor
• Oceanographers use T-S (Temperature-Salinity) diagrams to identify distinct water masses and trace their origins and mixing pathways
• The densest water masses form at high latitudes: Antarctic Bottom Water (AABW) is the coldest and densest, filling most of the deep global ocean; North Atlantic Deep Water (NADW) is cold and relatively salty

PART 4 - ROLE IN OCEAN CIRCULATION

1. In the North Atlantic, warm surface water releases heat to the atmosphere and becomes denser (colder + saltier from evaporation)
2. It sinks to form NADW and flows southward as deep water
3. Antarctic waters produce AABW (the densest ocean water), spreading along the ocean floor globally
4. This deep water slowly upwells in other ocean basins, returning to the surface
5. Surface currents complete the loop

Quick Reference Summary

Marine Resources and Their Utilization

CATEGORY 1 - LIVING (BIOTIC) MARINE RESOURCES

1. Fisheries

• Pelagic fisheries - open-water fish like tuna, sardines, anchovies, herring, mackerel
• Demersal fisheries - bottom-dwelling species like cod, haddock, flatfish
• Coastal/inshore fisheries - near-shore species, artisanal fishing communities

• Direct human consumption (fresh, frozen, canned, dried, salted)
• Fish meal and fish oil - used in animal feed, aquaculture, poultry and livestock industries
• Pharmaceutical and nutraceutical products (omega-3 fatty acids, fish liver oils)
• Industrial uses (glue, leather, fertilizer)

2. Aquaculture (Mariculture)

• Finfish: Salmon, sea bass, sea bream, tilapia, milkfish
• Shellfish: Oysters, mussels, clams, scallops, shrimp/prawns, lobster, crab
• Seaweed/algae: Kelp, nori, agar-producing species

• Human food supply (accounts for over 50% of global seafood consumption now)
• Agar and carrageenan (food additives, gelling agents, pharmaceutical capsules)
• Biofuel feedstock (microalgae)
• Bioremediation of coastal waters

3. Marine Plants and Algae

• Red algae (Rhodophyta): Source of agar (used in food, microbiology media) and carrageenan (food thickener)
• Brown algae (Phaeophyta): Source of alginates (used in food, pharmaceuticals, textiles, paper), kelp harvested for food and fertilizer
• Green algae (Chlorophyta): Used as food in many Asian countries

• Spirulina and Chlorella: High-protein health supplements
• Dunaliella: Source of beta-carotene
• Nannochloropsis: Omega-3 fatty acid production
• Potential for large-scale biofuel production

4. Marine Mammals

• Eco-tourism (whale watching - a multi-billion dollar industry)
• Scientific research
• Limited subsistence hunting by indigenous communities

5. Marine Biotechnology and Pharmaceutical Resources

6. Coral Reefs

• Fisheries support - reefs are nurseries for 25% of all marine fish species
• Coastal protection - act as natural breakwaters, protecting shorelines from waves and storm surges
• Tourism - reef-based tourism generates billions of dollars annually (e.g., Great Barrier Reef)
• Bioprospecting - source of bioactive compounds
• Building materials - coral limestone historically used in construction (now largely banned)

CATEGORY 2 - NON-LIVING (ABIOTIC) MARINE RESOURCES

1. Offshore Oil and Gas

• Energy production (electricity, heating, transport fuels)
• Petrochemicals (plastics, fertilizers, medicines)
• Major offshore fields: North Sea, Gulf of Mexico, Persian Gulf, offshore Brazil (pre-salt), West Africa

2. Deep-Sea Mineral Resources

a) Polymetallic (Manganese) Nodules

• Potato-sized concretions on the abyssal seafloor, most abundant in the Clarion-Clipperton Zone (CCZ) in the Pacific
• Contain: manganese, nickel, cobalt, copper, molybdenum, and rare earth elements
• Critical for electric vehicle batteries and renewable energy technology
• Tonnages in the CCZ alone exceed known terrestrial reserves of many metals
• Deep-sea mining not yet commercial; active exploration underway

b) Cobalt-rich Ferromanganese Crusts

• Layered encrustations on flanks of underwater volcanoes (seamounts)
• Rich in cobalt, nickel, platinum, rare earth elements
• ~7.5 billion dry tons estimated in the Pacific Ocean Prime Crust Zone

c) Polymetallic (Seafloor Massive) Sulfide Deposits

• Form at hydrothermal vents (black smokers) along mid-ocean ridges
• Contain: copper, zinc, iron, gold, silver
• Located along plate boundaries in all ocean basins

3. Beach and Nearshore Minerals (Placer Deposits)

4. Seawater as a Resource

• Desalination: Produces fresh water for drinking and irrigation (major industry in Middle East, North Africa, water-scarce regions). Global desalination capacity exceeds 100 million m³/day
• Salt extraction: Sea salt harvested from evaporation pans worldwide
• Magnesium: Commercially extracted from seawater (seawater contains ~1.3 g/L magnesium)
• Bromine: ~70% of world's bromine extracted from seawater
• Potassium, uranium: Theoretically present in large quantities; extraction not yet economic at scale

CATEGORY 3 - MARINE ENERGY RESOURCES

1. Offshore Wind Energy

• Fastest-growing renewable energy source globally
• Offshore wind turbines generate electricity with higher and more consistent wind speeds than onshore
• Major installations: North Sea (UK, Germany, Denmark, Netherlands), offshore China
• Global installed offshore wind capacity exceeded 70 GW as of 2024, projected to grow massively

2. Tidal Energy

• Harnesses kinetic energy of tidal currents or potential energy of tidal rise and fall
• Tidal barrages: Dam-like structures across estuaries (La Rance, France - operating since 1966; Sihwa, South Korea)
• Tidal stream turbines: Underwater turbines in fast tidal channels (Pentland Firth, Scotland)
• Predictable, reliable, but geographically limited to areas with high tidal range or fast currents

3. Wave Energy

• Vast resource - global wave power estimated at ~2,000 TWh/year
• Various converter technologies: oscillating water columns, point absorbers, attenuators
• Still largely at pre-commercial/demonstration stage

4. Ocean Thermal Energy Conversion (OTEC)

• Exploits the temperature difference between warm surface water (~25°C) and cold deep water (~4°C) in tropical regions
• Used to drive a heat engine and generate electricity
• Also produces fresh water as a by-product
• Most viable in tropical areas (Hawaii, Pacific Islands, Caribbean)
• Still experimental/small-scale

5. Salinity Gradient Energy (Osmotic Power)

• Harnesses energy released when fresh water and salt water mix
• Pilot plants tested in Norway and the Netherlands
• Theoretically very large resource at river mouths; technology still developing

CATEGORY 4 - OTHER MARINE RESOURCES

1. Marine Transportation and Trade

• Over 90% of world trade by volume travels by sea
• Ports, shipping lanes, and the sea itself are strategic and economic resources
• Submarine telecommunications cables carry ~95% of global internet traffic

2. Tourism and Recreation

• Coastal and marine tourism is one of the largest sectors of the blue economy
• Includes beach tourism, scuba diving, snorkeling, sport fishing, whale watching, cruises
• Generates hundreds of billions of dollars annually worldwide

3. Marine Genetic Resources

• Unique organisms at hydrothermal vents, cold seeps, and the deep sea contain genes and enzymes of immense biotechnological value
• Thermostable enzymes from hydrothermal vent bacteria (e.g., Taq polymerase from hot springs) are fundamental to PCR technology

Summary Table

Legal Framework

• Territorial Sea: 0-12 nm - full national sovereignty
• Exclusive Economic Zone (EEZ): 0-200 nm - exclusive rights to exploit natural resources
• Continental Shelf: Up to 350 nm for seabed resources
• High Seas / "The Area": Beyond 200 nm - governed by ISA (minerals) and international treaties (fisheries, biodiversity)

Bottom Topography of the Atlantic, Indian, and Pacific Oceans

PART 1 - UNIVERSAL FEATURES OF OCEAN FLOOR TOPOGRAPHY

A. Continental Shelf

• The submerged, gently sloping extension of the continent
• Depth: 0 to ~200 m
• Width: varies from a few km (tectonically active margins) to >500 km (passive margins)
• Covered by terrigenous sediments (sand, silt, mud) from rivers and coastal erosion
• Economically the most important zone (fisheries, oil/gas, sand/gravel)

B. Continental Slope

• Begins at the shelf break (~200 m) and descends steeply to the ocean floor
• Gradient: 3°-6° (much steeper than the shelf)
• Depth: 200 m to ~3,000-4,000 m
• Cut by submarine canyons (formed by turbidity currents)

C. Continental Rise

• A gently sloping apron of sediment at the base of the continental slope
• Formed by accumulation of turbidite sediments carried down by turbidity currents
• Depth: ~3,000 to 5,000 m
• Well-developed on passive margins (e.g., eastern North America, West Africa)

D. Abyssal Plains

• Flat, sediment-covered ocean floor at depths of 4,000-6,000 m
• Among the flattest surfaces on Earth
• Formed as turbidites and pelagic sediments bury underlying rough basaltic crust
• Cover ~40% of the ocean floor globally

E. Mid-Ocean Ridges

• Continuous underwater mountain chains marking divergent plate boundaries
• Sites of seafloor spreading and new oceanic crust formation
• Total length: ~65,000 km worldwide (longest mountain range on Earth)
• Rise 2,000-3,000 m above the surrounding ocean floor
• Have a central rift valley (slow-spreading ridges) or rounded crest (fast-spreading)

F. Ocean Trenches

• Long, narrow, steep-walled depressions marking subduction zones (convergent plate boundaries)
• Deepest features on Earth (up to 11,000 m)
• Found at the edges of ocean basins, typically parallel to island arcs or mountain ranges

G. Seamounts and Guyots

• Seamounts: Isolated volcanic peaks rising >1,000 m from the ocean floor, but not reaching the surface
• Guyots: Flat-topped seamounts whose peaks have been eroded by wave action when they were at or above sea level, then subsided
• Thousands exist across all ocean basins

H. Submarine Ridges, Plateaus, and Fracture Zones

• Aseismic ridges: chains of volcanic islands/seamounts tracing hotspot paths (e.g., Hawaiian-Emperor chain)
• Oceanic plateaus: large elevated areas of thickened ocean crust
• Fracture zones: long linear scar-like features offsetting mid-ocean ridges

PART 2 - ATLANTIC OCEAN TOPOGRAPHY

A. Mid-Atlantic Ridge (MAR)

• Runs ~16,000 km from the Arctic Ocean (where it joins the Gakkel Ridge) south to near the tip of Africa (Bouvet Triple Junction)
• Divides the Atlantic into eastern and western basins
• Width: ~1,600 km; rises 2,000-3,000 m above surrounding floor
• A slow-spreading ridge (~2.5 cm/year) with a prominent central rift valley 50-75 km wide
• The Atlantic basin is widening at this rate - it was once a narrow seaway (Tethys-related) and continues to open
• Where it rises above sea level: Iceland (world's best surface exposure of a mid-ocean ridge), Azores, Ascension Island, St. Helena, Tristan da Cunha
• Near the equator, the MAR is cut by the Romanche Fracture Zone, a deep transform fault (~7,758 m)

B. Western Atlantic Basins (West of MAR)

C. Eastern Atlantic Basins (East of MAR)

D. Trenches of the Atlantic

• Puerto Rico Trench - deepest point in the Atlantic at 8,376 m (Milwaukee Deep); located at a transform fault zone between the North American and Caribbean plates; just north of Puerto Rico
• South Sandwich Trench - in the far South Atlantic, near the South Sandwich Islands; ~8,428 m deep (some measurements make it deeper than Puerto Rico)
• Romanche Trench - an equatorial fracture zone; ~7,758 m

E. Notable Atlantic Features

• Walvis Ridge: Aseismic ridge extending from the MAR to SW Africa; hotspot trail of Tristan da Cunha
• Rio Grande Rise: Submerged plateau in the South Atlantic; conjugate to the Walvis Ridge
• Bermuda Rise: Large hotspot swell in the North Atlantic, topped by Bermuda seamount/atoll
• New England Seamounts: Chain of extinct volcanoes off the eastern US coast
• Reykjanes Ridge: SW extension of the MAR from Iceland; lacks a rift valley (warmer, more active)
• Celtic Shelf, North Sea: Extensive, shallow (< 200 m) continental shelf areas

PART 3 - INDIAN OCEAN TOPOGRAPHY

A. The Ridge System

B. Major Basins and Abyssal Plains

C. The 90° East Ridge (Ninetyeast Ridge)

• One of the most remarkable features of the Indian Ocean
• A nearly straight aseismic ridge running along ~90°E longitude for ~5,000 km
• Formed by the Kerguelen hotspot as the Indian plate moved northward
• Separates the eastern and central basins
• Now mostly submerged; peaks rise to ~1,000-2,000 m above the abyssal plain

D. Trenches of the Indian Ocean

E. Notable Indian Ocean Features

• Mascarene Plateau and Seychelles Bank: Shallow submerged plateaus, remnants of continental microplates from the India-Madagascar breakup
• Kerguelen Plateau: A massive oceanic plateau in the southern Indian Ocean; among the world's largest; formed by the Kerguelen hotspot; ~200 m to 500 m deep at shallowest points
• Broken Ridge: Aseismic ridge south of Australia; conjugate to the Kerguelen Plateau
• Chagos-Laccadive Ridge: Aseismic hotspot trail of the Réunion hotspot (same that erupted the Deccan Traps); runs N-S connecting the Maldives and Lakshadweep Islands to Réunion
• Madagascar Ridge: Submarine continuation of Madagascar southward

PART 4 - PACIFIC OCEAN TOPOGRAPHY

A. East Pacific Rise (EPR)

• The Pacific's main mid-ocean ridge
• A fast-spreading ridge (up to 16-18 cm/year in some sections - the fastest on Earth)
• Because of its fast spreading, it is broader and smoother than the MAR, with a low profile and no prominent central rift valley (lava flows fill in any depression quickly)
• Runs from near the Gulf of California southward to the Pacific-Antarctic Ridge
• Connects to the Juan de Fuca Ridge in the NE Pacific (off Oregon/Washington) and the Galapagos Spreading Center
• The East Pacific Rise is closer to the eastern (Americas) side, making the western Pacific much larger and older

B. Major Pacific Basins and Abyssal Plains

C. Trenches - The Pacific Dominates

D. Volcanic Island Chains and Aseismic Ridges

• Hawaiian-Emperor Chain: The classic hotspot trail - Emperor Seamounts (now submerged, trending NNW) and Hawaiian Islands (trending NW-SE); the chain is ~5,800 km long. Mauna Kea, measured from its base on the ocean floor, is the tallest mountain on Earth (~10,200 m)
• Line Islands: Aseismic ridge chain running N-S in the central Pacific
• Tuamotu Archipelago: Volcanic island and atoll chain in the South Pacific (hotspot trail)
• Marshall Islands, Caroline Islands: Atolls and guyots in the W. Pacific
• Mid-Pacific Mountains: Submerged seamount range in the central North Pacific; many flat-topped guyots
• Shatsky Rise, Hess Rise, Ontong Java Plateau: Large oceanic plateaus in the NW and SW Pacific; Ontong Java Plateau is the largest oceanic plateau on Earth (~5 million km²)

E. Western Pacific Features

• Ryukyu Trench and Arc: SW of Japan
• Mariana Arc: Island arc parallel to the Mariana Trench
• Philippine Sea Plate: Entirely oceanic plate; bounded by trenches
• Coral Sea and Tasman Sea: Contain the Lord Howe Rise, part of the drowned microcontinent of Zealandia (mostly submerged continent that includes New Zealand)

Comparison Summary

Ocean Deposits (Marine Sediments)

PART 1 - CLASSIFICATION OF OCEAN DEPOSITS

1. By origin (genetic classification) - most scientifically meaningful
2. By location (neritic vs. pelagic) - based on where they accumulate

PART 2 - CLASSIFICATION BY ORIGIN (GENETIC)

A. Terrigenous (Lithogenous) Sediments

• Rivers (the largest contributor - carry silt, sand, clay)
• Wind (aeolian transport - especially important for fine clay and dust over open ocean)
• Glaciers (ice-rafted debris - boulders, gravels, unsorted material dropped by melting icebergs)
• Coastal erosion by waves
• Volcanic eruptions (volcanogenic sediments - ash falls, tephra layers)

• Quartz, feldspars, clay minerals (illite, kaolinite, chlorite, smectite)
• Rock fragments, heavy minerals
• Volcanic ash and glass

• Most abundant near continental margins (shelves, slopes, and rises)
• Thicker deposits near major rivers (e.g., Amazon Fan, Bengal Fan - one of the world's largest sediment fans, fed by the Ganges-Brahmaputra rivers, extending ~3,000 km into the Indian Ocean)
• At high latitudes: glacial-marine sediments (ice-rafted debris - IRD) are dominant
• Fine-grained wind-blown particles (aeolian dust) can reach far into the open ocean (e.g., Saharan dust deposited in the North Atlantic and Caribbean)

B. Biogenous (Biogenic) Sediments

i. Calcareous (Carbonate) Sediments

• CaCO₃ dissolves as pressure increases and temperature decreases with depth
• Below ~4,000-5,000 m, the rate of dissolution exceeds supply - no carbonate accumulates
• This critical depth is the CCD (Carbonate Compensation Depth)
• Above the CCD: calcareous ooze accumulates
• Below the CCD: carbonate-free sediments (siliceous ooze or red clay)
• The CCD varies by ocean: shallower in the Pacific (~3,500-4,500 m), deeper in the Atlantic (~5,000 m)
• The lysocline is the depth at which dissolution begins to increase significantly (above the CCD)

ii. Siliceous Sediments

• Diatom ooze: Found beneath high-productivity polar/subpolar zones, especially around Antarctica (Southern Ocean) and the North Pacific
• Radiolarian ooze: Found in the equatorial Pacific and Indian Ocean
• Siliceous ooze accumulates below the CCD where calcareous material has dissolved
• Silica also dissolves in seawater but less predictably than CaCO₃

C. Hydrogenous (Authigenic) Sediments

D. Cosmogenous Sediments

• Cosmic spherules: Tiny rounded particles of iron-nickel or silicate, formed from micrometeorites melting as they pass through the atmosphere
• Tektites: Glassy particles from large meteorite impacts melting crustal rocks; found in specific stratigraphic layers
• Iridium anomaly: The famous global layer of iridium-rich dust at the Cretaceous-Paleogene (K-Pg) boundary (~66 million years ago), marking the asteroid impact that caused the mass extinction - found worldwide in ocean sediment cores

PART 3 - CLASSIFICATION BY LOCATION

A. Neritic (Shallow-Water) Deposits

1. Littoral Deposits (Shoreline Zone)

• Sand and gravel on beaches and the immediate surf zone
• Constantly reworked by waves and longshore currents
• Composition reflects local geology and river input

2. Shelf Deposits

• Terrigenous muds and silts near river mouths and estuaries
• Relict sediments: coarser sands and gravels on outer shelves, actually deposited during lower sea levels during ice ages and not in equilibrium with present conditions
• Carbonate sediments: dominant on tropical shelves with little terrigenous input (e.g., Great Barrier Reef, Persian Gulf, Bahamas Banks - made of skeletal debris, oolites, coral fragments)
• Organic-rich muds: beneath upwelling zones (e.g., off Peru, Namibia); low oxygen preserves organic matter

3. Estuarine and Deltaic Deposits

• Fine-grained muds, silts, and organic matter at river mouths
• Major deltas (Mississippi, Nile, Niger, Ganges-Brahmaputra, Amazon) deposit enormous volumes of sediment

B. Pelagic (Deep-Sea) Deposits

• It accumulates incredibly slowly (~1 mm per 1,000 years)
• It is the default sediment where everything else dissolves or gets diluted
• Rich in authigenic minerals (manganese micronodules, cosmic spherules, fish teeth)
• Covers vast areas of the central Pacific, away from ridges and productivity zones

PART 4 - TURBIDITES AND SUBMARINE FANS

• Carve submarine canyons into the continental slope
• Deposit graded beds (turbidites) on the continental rise and abyssal plains
• Build enormous submarine fans at the base of continental slopes

• Bengal Fan (Indian Ocean): Largest sediment body on Earth; fed by Ganges-Brahmaputra; ~3,000 km long and up to 22 km thick
• Indus Fan: Second largest; fed by Indus River
• Amazon Fan: Atlantic Ocean
• Mississippi Fan: Gulf of Mexico
• Astoria Fan: North Pacific, off Oregon/Washington

PART 5 - DISTRIBUTION ACROSS THE OCEAN FLOOR

• Shallow water (< 200 m): Terrigenous sands/muds, carbonates, organic muds
• Mid-depth (200-4,000 m): Calcareous ooze (above CCD)
• Deep (4,000-5,000 m and below, CCD): Siliceous ooze or red clay (carbonate dissolved)
• Ridges and rises: Calcareous ooze (elevated above CCD)
• Trenches: Turbidites, terrigenous and pelagic mix

PART 6 - SIGNIFICANCE OF OCEAN DEPOSITS

Summary

Ocean Currents and Tides

PART 1 - OCEAN CURRENTS

A. Types of Ocean Currents

1. Surface Currents (Wind-Driven)

• Driven primarily by global wind patterns (trade winds, westerlies, polar easterlies)
• Affect the upper 100-200 m of the ocean (the mixed layer)
• Make up about 10% of all ocean water
• Direction is modified by the Coriolis effect, continental boundaries, and ocean basin geometry

2. Deep-Water Currents (Thermohaline)

• Driven by differences in water density caused by temperature and salinity variations
• Affect the remaining ~90% of ocean water
• Move much more slowly than surface currents (mm/sec vs. cm/sec to m/sec)
• Form the global ocean conveyor belt (thermohaline circulation)

B. Forces Driving Ocean Currents

1. Wind (Primary Driver of Surface Currents)

• Global winds drag on the ocean surface, pushing water in the direction of wind flow
• Trade winds (blow westward near the equator) drive equatorial currents westward
• Westerlies (blow eastward in mid-latitudes) drive mid-latitude currents eastward
• Polar easterlies drive currents westward at high latitudes

2. Coriolis Effect

• Due to Earth's rotation, moving objects (including water) are deflected:
  • Right in the Northern Hemisphere
  • Left in the Southern Hemisphere
• This deflection creates circular gyres rather than straight currents
• The Coriolis effect is zero at the equator and maximum at the poles
• It also creates the Ekman spiral: each successive layer of water below the surface is deflected slightly more, creating a spiral pattern down to ~100 m; net water transport (Ekman transport) is 90° to the right (NH) or left (SH) of the wind

3. Density Differences (Temperature and Salinity)

• Cold, salty water is denser and sinks; warm, fresh water is lighter and rises
• These density-driven vertical movements drive thermohaline (deep) circulation
• Temperature and salinity together determine density: thermohaline = thermo (heat) + haline (salt)

4. Gravity and Pressure Gradients

• Water piles up in areas of persistent wind convergence (e.g., center of subtropical gyres)
• This creates a pressure gradient that drives water away from the pile - balanced by Coriolis to create geostrophic flow

5. Continental Boundaries

• Land masses deflect, channel, and redirect currents
• Form the western and eastern boundary currents of ocean gyres

C. Ocean Gyres

• Northern Hemisphere gyres: rotate clockwise
• Southern Hemisphere gyres: rotate counterclockwise

• North/South equatorial current (westward, driven by trade winds)
• Western boundary current (fast, narrow, warm, poleward)
• West wind drift / eastward current (driven by westerlies)
• Eastern boundary current (slow, broad, cool, equatorward)

D. Western Boundary Currents (Warm, Fast, Narrow)

E. Eastern Boundary Currents (Cold, Slow, Broad)

F. Major Equatorial Currents

G. Notable Named Currents

H. Thermohaline Circulation (Deep Ocean Conveyor Belt)

1. Warm, salty surface water flows poleward (e.g., via Gulf Stream/North Atlantic Drift)
2. In the North Atlantic (near Iceland, Greenland, Labrador Sea) the water cools and becomes denser
3. Dense water sinks to form North Atlantic Deep Water (NADW) and flows southward as a deep current
4. In Antarctica, extreme cooling and brine rejection during sea ice formation creates the densest ocean water - Antarctic Bottom Water (AABW) - which sinks and spreads along the ocean floor globally
5. These deep waters slowly upwell in the Indian and Pacific Oceans (especially near Antarctica)
6. Upwelled water returns to the surface, warms, and continues the cycle
7. The complete circuit takes approximately 1,000 years

• Transports enormous amounts of heat globally (Gulf Stream carries ~1.3 petawatts of heat northward)
• Regulates Northern Hemisphere climate (without it, NW Europe would be ~5-8°C colder)
• Distributes oxygen and nutrients to the deep ocean
• Plays a major role in the global carbon cycle
• Climate change concern: freshwater from melting ice sheets could weaken the AMOC (Atlantic Meridional Overturning Circulation), potentially disrupting global climate patterns

I. Upwelling and Downwelling

• Occurs along eastern ocean boundaries where Ekman transport pushes surface water offshore (e.g., Peru, California, Benguela, Canary)
• Also occurs in the Southern Ocean around Antarctica
• Brings nutrients to the sunlit surface zone → highly productive fisheries
• Brings CO₂-rich water to surface → important in carbon cycle

• Occurs where surface water converges (e.g., center of gyres, polar regions)
• Transports dissolved oxygen to the deep ocean

J. Effects of Ocean Currents

PART 2 - OCEAN TIDES

A. Causes of Tides

1. Lunar Gravitation (Primary Cause)

• The Moon's gravity pulls ocean water toward it, creating a tidal bulge on the side of Earth facing the Moon
• On the opposite side, a second bulge forms due to inertia (the centrifugal effect of Earth-Moon system orbiting a common center of mass) - the Moon's gravity is slightly weaker there, so water "bulges out"
• These two bulges are the high tides; the areas between them experience low tides
• As Earth rotates under these bulges, most places experience two high tides and two low tides per day
• The Moon's gravitational force on oceans is about 2.2 times stronger than the Sun's

2. Solar Gravitation (Secondary Cause)

• The Sun also exerts a tidal force, about 46% as strong as the Moon's
• Its effect combines with or counteracts the Moon's depending on alignment

3. Earth's Rotation

• Earth rotates beneath the tidal bulges, creating the daily tidal cycle
• A lunar day is ~24 hours 50 minutes (slightly longer than solar day because Moon moves in its orbit), so tides advance ~50 minutes later each day

B. Types of Tides

1. Based on Frequency (Tidal Cycle Types)

2. Based on Sun-Moon Alignment (Tidal Range)

Spring Tides

• Occur during new moon and full moon (Moon-Earth-Sun or Sun-Earth-Moon alignment = syzygy)
• Moon and Sun tidal forces combine (act in the same direction)
• Result: highest high tides and lowest low tides - greatest tidal range
• Occur approximately every 2 weeks
• Not named after the season - from Old English "springan" meaning "to leap or surge"

Neap Tides

• Occur during first quarter and third quarter moon (Moon-Earth-Sun form a right angle = quadrature)
• Moon and Sun tidal forces partially cancel each other
• Result: lower high tides and higher low tides - smallest tidal range
• Tidal range is typically 10-30% less than average
• Occur approximately every 2 weeks, between spring tides

3. Other Tidal Variations

Perigean Tides

• When the Moon is at perigee (closest to Earth in its elliptical orbit), tidal forces are stronger
• Combined with spring tide = "King Tide" or Perigean Spring Tide - exceptionally high tides

Apogean Tides

• Moon at apogee (farthest from Earth) - weaker tidal forces, smaller tidal range

Equinoctial Tides

• Near the spring and autumn equinoxes, when the Sun is directly over the equator - slightly larger tidal ranges due to Sun-Earth alignment geometry

C. Tidal Range

D. Tidal Currents

• Flood current: flows toward shore as tide rises
• Ebb current: flows away from shore as tide falls
• Slack water: the brief period of little to no current between flood and ebb
• In narrow channels and estuaries, tidal currents can be extremely powerful (e.g., tidal races in the English Channel, Pentland Firth)
• Tidal bores: in some rivers (Severn in UK, Qiantang in China, Amazon in Brazil), the incoming flood tide forms a wave that travels upstream as a wall of water

E. Importance and Applications of Tides

Summary Comparison

Ekman Transport and Its Significance

1. Historical Background

2. The Mechanism - Step by Step

Step 1: Wind Stress on the Ocean Surface

Step 2: The Coriolis Deflection

• In the Northern Hemisphere: deflects moving water to the right of its direction of motion
• In the Southern Hemisphere: deflects it to the left

Step 3: The Ekman Spiral

• Moves more slowly (friction diminishes with depth)
• Is deflected further to the right (or left) by the Coriolis force

Wind direction →
Surface layer:       deflected ~45° to the right
10 m depth:          deflected further right, slower
20 m depth:          even more to the right, even slower
...
~100 m depth:        moving in almost the OPPOSITE direction to the wind, at very slow speed

Step 4: Net Ekman Transport - The 90° Result

• Northern Hemisphere: net transport is 90° to the right of the wind
• Southern Hemisphere: net transport is 90° to the left of the wind

3. Mathematical Expression

M = τ / f

• τ (tau) = wind stress (force per unit area, in N/m²)
• f = Coriolis parameter = 2Ω sin(φ), where Ω = Earth's angular velocity and φ = latitude
• M = volume transport per unit width (m²/s)

• Ekman transport increases with stronger wind stress
• Ekman transport is infinite at the equator (Coriolis parameter f = 0 there, making the concept inapplicable at the equator)
• It is stronger at lower latitudes (where f is smaller, transport per unit wind stress is larger)

4. Ekman Pumping

Downwelling (Ekman Convergence)

• In the center of subtropical gyres, winds rotate clockwise (NH) / counterclockwise (SH)
• Ekman transport pushes water toward the center from all sides
• Water piles up and is pushed downward - Ekman downwelling
• Creates a warm water lens (thermocline domes downward) in gyre centers
• These regions are nutrient-poor, low-productivity "ocean deserts"

Upwelling (Ekman Divergence)

• Where winds cause Ekman transport to move water away from a region, deeper water must rise to replace it
• This is Ekman upwelling or Ekman-driven upwelling
• Brings cold, nutrient-rich water to the surface
• Creates highly productive marine ecosystems

5. Coastal Ekman Upwelling - Key Examples

West Coast of Continents (Eastern Boundary Currents)

• Prevailing winds blow southward (equatorward) along the coast
• Ekman transport pushes surface water 90° to the right = offshore (westward)
• Surface water moves away from the coast → replaced by cold, deep water rising from below
• Result: coastal upwelling → cold California Current → rich fisheries

• Trade winds blow northward (equatorward) along the coast
• Ekman transport pushes surface water 90° to the left = offshore (westward)
• Same result: coastal upwelling → Humboldt Current → historically world's most productive fishery (anchovy, sardine)

• South Atlantic trade winds drive Ekman transport offshore
• Upwelling supports enormous fisheries and the Namib Desert (cold current prevents rainfall onshore)

• Northeast trade winds drive Ekman transport offshore
• Major upwelling system supporting North African fisheries

Eastern Boundary vs. Western Boundary Coasts

• Eastern ocean boundaries (west coasts of continents): winds blow equatorward → Ekman transport pushes water offshore → upwelling → cold, productive
• Western ocean boundaries (east coasts of continents): winds blow poleward → Ekman transport pushes water onshore → downwelling → warm western boundary currents (Gulf Stream, Kuroshio)

6. Equatorial Upwelling

• Trade winds blow westward
• In the NH, Ekman transport is to the right (northward)
• In the SH, Ekman transport is to the left (also northward, meaning away from equator = southward)
• Net result: Ekman transport diverges away from the equator on both sides
• Deep water rises along the equator = equatorial upwelling
• This is why the equatorial Pacific has a visible cold tongue of productive water despite being in the tropics

7. Role in El Niño (ENSO)

• Normal (La Niña-like) conditions: Strong trade winds → strong westward Ekman transport → upwelling along Peru coast and equatorial E. Pacific → cold SSTs
• El Niño onset: Trade winds weaken or reverse → Ekman transport weakens → upwelling ceases → warm water spreads eastward → dramatic warming of E. Pacific
• This disrupts fisheries (Peruvian anchovy collapse), alters global rainfall patterns, and affects hurricane activity

8. Significance of Ekman Transport - Summary

9. Summary Diagram (Conceptual)

WIND BLOWS NORTHWARD (Northern Hemisphere)
          ↑ Wind
          |
Surface layer: deflected 45° RIGHT (to east)
10 m layer:    deflected more to right, slower
20 m layer:    even more to right, slower still
...
~100 m:        moving southward (opposite wind), very slow
          
NET EKMAN TRANSPORT = 90° to RIGHT of wind = EASTWARD
          →→→→→ (bulk water moves east)

If coast is to the EAST:
  Water piles up against coast → DOWNWELLING (sinks)

If coast is to the WEST:
  Water moves AWAY from coast → UPWELLING (cold deep water rises)