Hydrosphere | Exam Fusion Prep

💧 Distribution of Water

Water covers 70.8% of the Earth's surface

Category	Distribution
Saline / Salty Water (97.5%)	Oceans hold about 96.5% of total water; saline lakes about 0.006%. Total saline water is ~97.5%.
Fresh Water (2.5%)	Ice/glaciers: ~1.74% of total water (~68.7% of freshwater); fresh groundwater: ~0.76% total (~30.1% freshwater); freshwater lakes: ~0.007% total (~0.26% freshwater).

🔄 Water Cycle

Conversion of water into vapour and vapour again into water
Key Processes: Evaporation, Transpiration, Condensation
Evaporation: Water → Water vapour (Liquid → Gas)
Condensation: Water vapour → Water

⚡ Quick Recall

Of freshwater, ice/glaciers ~68.7% and fresh groundwater ~30.1%. These are reservoir shares, not a statement that all that water is readily usable.

🌐 Oceans of the World

Decreasing size order Pacific > Atlantic > Indian > Antarctic > Arctic

Ocean	Key Features
Pacific Ocean (Semicircular)	Largest/deepest ocean; Challenger Deep ~10,935 m in the Mariana Trench
Atlantic Ocean ('S' shape)	Sargasso Sea (coastless sea) • 'S' shaped
Indian Ocean (Triangular)	Deepest trench – Java/Sunda Trench (7,290 m) • Largest sea in northern Indian Ocean is the Arabian Sea
Antarctic Ocean	Surrounds the Antarctic continent → also called the Southern Ocean
Arctic Ocean	Widest continental shelf

⚡ Quick Recall

The Pacific Ocean holds the deepest point on Earth (Challenger Deep, Mariana Trench); the Indian Ocean's deepest point (Java/Sunda Trench) is much shallower in comparison.

🌉 Major Straits of the World

Strait	Seas Connected	Geographical Location
Malacca	Andaman Sea and South China Sea	Indonesia – Malaysia
Palk	Bay of Bengal / Palk Bay side and Gulf of Mannar side	India – Sri Lanka
Bering	Bering Sea (Pacific) and Chukchi Sea (Arctic)	Alaska – Russia
Davis	Baffin Bay and Atlantic Ocean	Greenland – Canada
Dover	English Channel and North Sea	England – France
Gibraltar	Mediterranean Sea and Atlantic Ocean	Spain – Morocco
Florida	Gulf of Mexico and Atlantic Ocean	USA – Cuba
Bass	Tasman Sea and Southern Ocean	Australia
Sunda	Java Sea and Indian Ocean	Indonesia
Hormuz	Persian Gulf and Gulf of Oman	Oman – Iran
Torres	Arafura Sea and Coral Sea	Papua New Guinea – Australia
Bosphorus	Black Sea and Sea of Marmara	Turkey
Makassar	Java Sea and Celebes Sea	Indonesia
Bab-el-Mandeb	Red Sea and Gulf of Aden; between Yemen and Djibouti	Yemen – Djibouti

📌 Grand Channel (6° Channel) Strait between Great Nicobar Island and Sumatra Island (Indonesia)

⚠ Exam Trap

Palk Strait (India-Sri Lanka) and Bab-el-Mandeb (Yemen-Djibouti) are both narrow but strategically important straits — often tested for the exact countries/seas they connect.

🌊 Ocean Floor and Their Reliefs

Measurement of ocean depth: Fathometer
Depth/height shown by: Hypsographic curve

Ocean Floor Feature	Key Details
(1) Continental Shelf	Region of mineral oil and natural gas • Dogger Bank (Western Europe), Grand Bank and Georges Bank (North America) – prominent fishing zones
(2) Continental Slope	Sediments occur; gravity flows can move material downslope toward the continental rise/deep sea.
(3) Deep Sea Plains / Abyssal Plains	Very low-gradient, sediment-covered regions of deep-ocean basins; not a fixed 75–90% of ocean area.

📌 Other Ocean Landforms Bay & Gulf, Spit, Submarine Canyon, Seamount, Guyot, etc.

🕳️ Important Trenches of the World

Trench	Location	Depth (metres)
Mariana	Western Pacific Ocean	~10,935
Tonga	Central South Pacific Ocean	~10,800–10,860 (survey-dependent)
Puerto Rico	Atlantic Ocean (near West Indies)	~8,376
Diamantina Fracture Zone	Southeastern Indian Ocean	Old >8 km claim unreliable; Indian Ocean depth record lies in Java/Sunda Trench
Sunda (Java Trench)	Eastern Indian Ocean	7,290

⚡ Quick Recall

Challenger Deep, Mariana Trench, Pacific: about 10,935 m in the measured estimate used by OP.

🌡️ Temperature of Ocean Water

Average temperature (near equator) – Approx 27°C (decreases towards the poles)
Highest temperature found between Tropic of Cancer and Tropic of Capricorn

Term	Meaning
Pycnocline	Represents density gradient in water body
Halocline	Represents salinity gradient in water body
Thermocline	Represents variation in temperature with depth

🧂 Salinity of Ocean Water (Average – 35‰)

Amount of salt present per thousand grams of water (‰)
Average ocean salinity – 35 grams per thousand grams (35‰)
Salinity may increase or decrease with depth, depending on water masses and region.
Highest salinity band – Between 20°–40° North and 10°–30° South latitudes

🏔️ Highly Saline Lakes — Values Vary

Water Body	Salinity / Details
Dead Sea — Jordan and Israel/West Bank	Roughly 340‰; not an uncontested worldwide maximum
Van Lake (Turkey)	~22‰ (roughly 21–23 g/kg)
Great Salt Lake (USA)	Highly variable: historically roughly 60‰ to >270‰, depending on arm/water level

📌 Fast Facts – Salinity

Northern Indian Ocean contrast: Arabian Sea generally >35; Bay of Bengal often <34.
Instrument to measure salinity: Salinometer
Normal salinity at Equator despite high evaporation (due to heavy rainfall balancing it)
Chilika, Odisha: Asia’s largest brackish-water lagoon
Southern Ocean surrounds the Antarctic continent

🧪 Traditional Salt-Equivalent Composition — Salts Dissociate into Ions

Type of Salt	Salinity (‰)	Quantity (%)
Sodium Chloride (NaCl)	27.213	77.8
Magnesium Chloride	3.807	10.9
Magnesium Sulphate	1.658	4.7
Calcium Sulphate	1.260	3.6
Potassium Sulphate	0.863	2.5
Calcium Carbonate	0.123	0.3
Magnesium Bromide	0.076	0.2
Total	35	100

⚠ Exam Trap

Dead Sea ~340‰; Lake Van ~22‰; Great Salt Lake varies greatly by arm and lake level. Avoid an unqualified permanent world-highest ranking.

🪸 Coral Reefs

Coral = Coral Polyps – formed by marine organisms
Symbiotic relationship with zooxanthellae algae
Lime-dominant structures – formed from Calcium Carbonate (CaCO₃)
Live in colonies in warm, shallow, clear saltwater

✅ Conditions Required for Coral Growth

Many reef-building corals grow best around 23–29°C.
Ocean depth till sunlight can penetrate
Sediment-free water
Normal marine salinity
Presence of Submarine platforms (relatively flat, shallow area in ocean)

📂 Types of Coral Reefs

Type	Key Details
1. Fringing Coral Reef	South Florida, Islands of Malaysia and Solomon Islands, Gulf of Mannar, etc.
2. Barrier Reef	World's largest – Great Barrier Reef – Pacific Ocean (Australia)
3. Coral Atoll / Ring	World-famous Funafuti Atoll, Atolls of Lakshadweep Island, etc.

🥀 Coral Bleaching

Effect of global warming
Density of zooxanthellae algae declines
Concentration of photosynthesis pigments within the zooxanthellae falls

⚡ Quick Recall

Great Barrier Reef (Australia) = World's largest Barrier Reef · Funafuti Atoll = World-famous Coral Atoll — two different reef types, two different records.

🌊 HYDROSPHERE World Geography · Ch 20