Oceans and life, oceans under stress, and the High Seas Treaty

Detail

1. Oceans and life

• Oceans send rain to the continents.
• The sun heats ocean water, and the water evaporates.
• Winds carry this water vapour over the land.

• The vapour condenses and falls as rain. Without oceans, Earth would be a desert.

• "The planet's lungs": marine plants make more than half of the world's oxygen. These plants include:

• phytoplankton (tiny floating plants that drift near the sunlit surface)

• algae and seaweeds

• Oceans and people:

• Oceans gave people migration routes, trade, food, wars and coastal cultures.

• The Indian Navy's motto is Sam no Varunah ("May Varuna be good to us"). It calls on Varuna, the Vedic god of the waters.

• World Oceans Day is held by the UN on 8 June every year.

• NCERT names two threats to the oceans:
• plastic: millions of tonnes are dumped into the sea every year
• overfishing: fish are caught faster than they can breed and replace themselves

2. Oceans under stress: an overview

Stress	Main cause	Key figure	Main victims
Ocean acidification	The sea absorbs CO₂	Surface pH fell from ~8.2 to ~8.1 after industrialisation (~30% more acidic)	Corals, pteropods, oysters
Ocean deoxygenation	Warming and fertiliser runoff	~2% of ocean oxygen lost since 1960	Fish; life in oxygen minimum zones
Marine heatwave	Global warming	SST above the 90th percentile for ≥5 days	Corals (bleaching), fish
Microplastics	Broken plastic waste, fibres, cosmetics	Pieces smaller than 5 mm	Whole food chain
AMOC slowdown	Greenland meltwater makes the North Atlantic fresher	Very likely to weaken by 2100 (IPCC AR6)	Climate of Europe and the monsoon

3. Ocean acidification

• Ocean acidification means the ocean slowly becomes more acidic because it takes CO₂ out of the air.
• How it happens:
• We burn fossil fuels, so more CO₂ goes into the air.
• The ocean absorbs part of this CO₂. The gas reacts with water to form carbonic acid.
• The water's pH (a 0–14 scale; lower means more acidic) falls. At the surface it has dropped from about 8.2 to about 8.1 since industrialisation.

• The pH scale is logarithmic (each step means ten times more acidity), so this small drop means about 30% more acidity.

• Who is harmed: animals that build shells or skeletons from calcium carbonate. Acidic water makes this harder.

• corals
• pteropods ("sea butterflies": tiny swimming snails)

• oysters and other shellfish

• The planetary boundary has been crossed. A planetary boundary is a safe limit for an Earth system. Going past it risks harmful changes that may not reverse.

• The revised boundary is a 10% fall in the chemistry that shell-builders need, compared with pre-industrial times. Ocean conditions passed it around 2000 [7].
• By 2020, more than 40% of the surface ocean and up to 60% of the subsurface ocean (down to 200 m) had crossed the boundary (study published 2025) [7].
• Habitat suitable for these animals has shrunk:
  • tropical and subtropical coral reefs: down 43% [7]
  • polar pteropods: down by up to 61% [7]
  • coastal bivalves (two-shelled animals such as oysters and mussels): down 13% [7]

4. Ocean deoxygenation

• Ocean deoxygenation means the ocean is slowly losing its dissolved oxygen.
• Cause 1: warming. Warm water holds less oxygen than cold water. Warm surface water also mixes less with the deeper layers, so less oxygen reaches the deep sea.
• Cause 2: nutrient runoff.
• Fertiliser and sewage wash from farms and cities into the sea.
• These nutrients feed algal blooms (sudden, huge growths of algae).

• The algae die, and bacteria break them down. The bacteria use up the oxygen, which creates "dead zones".

• The ocean has lost about 2% of its oxygen since 1960.

• Oxygen minimum zones (OMZs) are layers of mid-depth water with very little oxygen. They are expanding.

• The Arabian Sea OMZ is one of the largest in the world, and it is spreading.

• Future and framing:

• Human-caused warming is very likely to cut ocean oxygen further, and the loss is expected to last for thousands of years [9].
• IOC-UNESCO has given a platform to a proposal to treat aquatic deoxygenation as a new planetary boundary [8].

5. Marine heatwaves

• Marine heatwave: a period when SST (sea surface temperature) stays above the 90th percentile for at least five days. In other words, the water is warmer than 90% of past readings for that place and season. This definition comes from Hobday et al. (2016).
• Effects:
• Coral bleaching: under heat stress, corals push out the colourful algae that live in them and feed them. The corals turn white and may die.
• Fish kills

• Stronger cyclones, because warm water gives storms more energy

• Trend: marine heatwaves became more frequent during the 20th century. They are expected to increase around the globe during the 21st century (IPCC AR6) [9].

• Indian angle: the tropical Indian Ocean is warming fastest among the tropical oceans. This adds to coral bleaching in the Gulf of Mannar, Lakshadweep and the Andaman and Nicobar Islands, and to stronger cyclones over the Arabian Sea and the Bay of Bengal.

6. Microplastics and the Great Pacific Garbage Patch

• Microplastics: plastic pieces smaller than 5 mm. They come from:
• large plastic waste that breaks into smaller bits
• synthetic fibres shed when clothes are washed

• microbeads in cosmetics

• They are found everywhere, from the Mariana Trench (western Pacific, the deepest place in the ocean, about 11 km) to Arctic sea ice.

• They enter food chains: plankton eat them, fish eat the plankton, and people eat the fish.
• Great Pacific Garbage Patch:
• Where: a large area of floating plastic in the North Pacific, between Hawaii and California.

• Why it forms: the North Pacific Gyre gathers it. A gyre is a huge ring of ocean currents that turns clockwise in the Northern Hemisphere. Its still centre traps floating waste.

• Global plastics treaty: talks have stalled.

• The second part of the fifth session of talks (INC-5.2) met in Geneva. More than 1,400 delegates from 183 countries took part [10].
• The talks ended on 15 August 2025 without agreement on a treaty text [10].
• On 7 February 2026, at INC-5.3, Ambassador Julio Cordano of Chile was elected the next chair of the negotiating committee [11].

7. Atlantic Meridional Overturning Circulation (AMOC)

• AMOC: the Atlantic part of the thermohaline circulation. The thermohaline circulation is the global "conveyor belt" of ocean water, driven by differences in temperature (thermo) and salinity (haline).
• How it works:
• Warm surface water flows north through the Gulf Stream and the North Atlantic Drift.
• In the far North Atlantic, near Greenland and Norway, this water cools and becomes salty and dense. It sinks.
• The cold deep water flows back south.

• The heat carried north keeps north-west Europe mild, warmer than other places at the same latitude.

• Why it may be slowing:

• Meltwater from Greenland makes the North Atlantic fresher (less salty).
• Fresher water is lighter, so it sinks less.

• The conveyor weakens.

• Outlook:

• IPCC AR6: the AMOC will very likely weaken this century, but an abrupt collapse before 2100 is unlikely (medium confidence).

• Some recent studies warn that a collapse could come sooner.

• If it collapses:

• Europe would cool sharply.
• Tropical rain belts (the ITCZ, Inter Tropical Convergence Zone: the low-pressure belt near the equator where the trade winds meet) would shift south.
• This could disturb the Indian monsoon.

8. Governance: the BBNJ Agreement ("High Seas Treaty")

• Full name: the Agreement under UNCLOS (UN Convention on the Law of the Sea) on the Conservation and Sustainable Use of Marine Biological Diversity of Areas Beyond National Jurisdiction.
• High seas: ocean areas outside every country's EEZ (Exclusive Economic Zone: the belt up to 200 nautical miles from the coast where a country controls resources).
• Timeline:
• Adopted: June 2023, after nearly two decades of talks [2].
• Ratifications: Morocco and Sierra Leone became the 60th and 61st parties in September 2025. This passed the 60-ratification mark the treaty needed [2].

• In force: 17 January 2026, when 81 countries had ratified it [3].

• Coverage: over two-thirds of the ocean's surface, which is over 90% of Earth's habitat by volume [3].

• Who has ratified: major economies such as China, Japan, France and Brazil have ratified. The USA signed in 2023 but has not ratified [2].

Pillar	What it does
Marine protected areas (MPAs)	Lets countries create protected areas on the high seas. These are needed for the 30x30 target: protecting 30% of land and sea by 2030, under the Kunming-Montreal Global Biodiversity Framework.
Environmental impact assessments (EIAs)	Activities on the high seas must be checked for harm before they start.
Marine genetic resources (MGRs)	Benefits from genes of deep-sea organisms (used, for example, in medicines) must be shared fairly.
Capacity-building and technology transfer	Helps poorer countries take part in ocean science and governance.

• The first Conference of the Parties (COP) must meet within one year of entry into force, that is, by January 2027 [3].
• India signed in 2024. Its ratification still depends on domestic legislation and had not been completed when the treaty came into force [3].

9. Related efforts

• International Seabed Authority (ISA): this UNCLOS body, based in Kingston, Jamaica, is still debating the mining code. The mining code is the set of rules for commercial deep-sea mining (for example, of polymetallic nodules).
• UN Decade of Ocean Science for Sustainable Development: 2021–2030.
• SDG 14, "Life Below Water": to conserve and sustainably use the oceans, seas and marine resources.
• India's Deep Ocean Mission (2021):
• Run by the Ministry of Earth Sciences (MoES).

• It supports India's Blue Economy by exploring deep-ocean resources [6].

• Samudrayaan and Matsya-6000:

• Samudrayaan is India's first crewed deep-ocean mission. It will carry three people to 6,000 m depth in Matsya-6000 [4][5].
• The vehicle: a fourth-generation, 25-tonne submersible. The crew sits in a titanium sphere 2.1 m across [4].
• Builders: NIOT (National Institute of Ocean Technology, Chennai) with VSSC/ISRO [4].
• Wet trials: held at L&T Shipyard, Kattupalli Port, Chennai, January–February 2025 [4].
• Launch: expected by the end of 2026 [5].
• India will become the sixth nation to build its own deep-ocean crewed submersible [4].

Prelims Hooks

• World Oceans Day: 8 June. NCERT's two named threats are plastic and overfishing.
• The Indian Navy's motto Sam no Varunah calls on Varuna, the Vedic god of the waters.
• Marine phytoplankton, algae and seaweeds make more than half of Earth's oxygen, so the oceans are called "the planet's lungs".
• Marine heatwave: SST above the 90th percentile for ≥5 days (Hobday et al., 2016). Trap: it is not "above 30 °C" and not "for a month".
• Microplastics are plastic pieces smaller than 5 mm.
• Great Pacific Garbage Patch: between Hawaii and California, gathered by the North Pacific Gyre. Trap: it is not in the South Pacific and not caused by the Kuroshio alone.
• Arabian Sea: has one of the world's largest oxygen minimum zones.
• BBNJ timeline: adopted June 2023, then the 60-ratification mark was crossed in September 2025, then it came into force on 17 January 2026. It falls under UNCLOS and covers over two-thirds of the ocean surface [2][3].
• Matsya-6000: 3 crew, 6,000 m, titanium sphere 2.1 m wide, built by NIOT with VSSC, under the Deep Ocean Mission (2021), MoES [4].
• AMOC parts: Gulf Stream and North Atlantic Drift (warm water going north); cold deep return flow (going south). IPCC AR6 says it will very likely weaken, and collapse before 2100 is unlikely.

Mains Points

• Several stresses at once, the "deadly trio" (GS-III, Environment): heat (marine heatwaves), acidification and deoxygenation act together. Each makes the others worse, and together they push coral reefs and fisheries towards collapse. More than 40% of the surface ocean had already crossed the acidification boundary by 2020 [7]. The Indian stakes are high: Gulf of Mannar and Lakshadweep reefs, the spreading Arabian Sea OMZ, and fishing livelihoods.
• The high seas need global governance: over two-thirds of the ocean belongs to no country. Before BBNJ, this led to a "tragedy of the commons" (no one owns it, so everyone overuses it). BBNJ's MPAs, EIAs and benefit-sharing on marine genetic resources [3] are key to 30x30. India must ratify the treaty, and it must also balance BBNJ protection against its deep-sea mining interests (ISA mining code, Deep Ocean Mission).
• AMOC as a tipping point: Greenland melt freshens the North Atlantic, which weakens sinking, which slows the AMOC. The effects reach beyond Europe: a southward shift of the ITCZ could weaken the Indian monsoon, which threatens food and water security.
• Plastic governance gap: microplastics are found from the Mariana Trench to the Arctic. Yet global treaty talks broke down at INC-5.2 (August 2025) [10]. India relies on domestic tools: the single-use plastic ban (2022), Extended Producer Responsibility (making companies responsible for the plastic waste they produce) and coastal clean-ups.