Seamounts and Guyots
The ocean floor also features isolated volcanic structures. Seamounts are underwater volcanic mountains that rise from the seafloor but do not reach the surface. Over millennia, some of these mountains may have their summits eroded by wave action; when they become flat-topped and are subsequently submerged, they are known as guyots.
Fig. 1.2. Submarine relief
Ocean Water Movement: Waves, Tides, and Currents
Ocean water is in constant motion, driven by various physical forces. These movements are not just physical phenomena; they influence climate, aid travel, and support fishing activities.
Waves
Waves are the rhythmic rising and falling of the ocean surface, primarily caused by winds blowing across the water. They carry energy across vast distances and act as "coastal architects," shaping shorelines through erosion and the creation of features like sea caves, arches, and stacks.
Tides
Tides are the daily rise and fall of sea levels caused by the gravitational pull of the Sun and the Moon.
- Spring Tides: Occur when the Sun, Earth, and Moon align in a straight line (during full and new moons), resulting in exceptionally high high tides and low low tides.
- Neap Tides: Occur when the Moon is in its first- or third-quarter phases, causing the gravitational pulls to act in different directions, which reduces the difference between high and low tide.
Tides are crucial for navigation—allowing ships to enter harbors safely—and for generating tidal energy.
Currents
Ocean currents are continuous streams of water flowing in definite directions. They are driven by winds, the Earth's rotation (the Coriolis force), and differences in temperature and salinity. Currents are classified as warm currents (flowing from warmer regions) or cold currents (flowing from colder regions). Where warm and cold currents meet, nutrient-rich waters are created, forming highly productive fishing grounds.
Maritime Zones and the Law of the Sea
To manage the vast resources of the ocean and prevent conflict, international laws define specific areas of control known as maritime zones. These rules are primarily governed by the United Nations Convention on the Law of the Sea (UNCLOS).
- Territorial Waters: The area closest to a country's coast, where the nation has near-complete control, though foreign ships enjoy the right of innocent passage.
- Contiguous Zone: Extends up to 24 nautical miles from the baseline, allowing limited control over customs and immigration.
- Exclusive Economic Zone (EEZ): Extending up to 200 nautical miles, a country has special rights to exploit resources like fish, oil, and gas within this zone.
- High Seas: Beyond the EEZs lie the international waters, which belong to no single nation and are considered the "global commons".
Exam Tip: The Nautical Mile
Remember that a nautical mile is a unit of measurement used in maritime navigation, defined as exactly 1,852 metres.
The Blue Economy and Marine Resources
As humanity relies more on the sea, the concept of the Blue Economy has become central to sustainable development. The World Bank defines it as the sustainable use of ocean resources to promote economic growth and jobs while preserving the health of the marine ecosystem.
Marine resources are categorized into:
- Living Resources: Such as fish, seafood, and marine organisms.
- Non-living Resources: Including oil, natural gas, minerals, and renewable "blue energy" from tides and waves.
Protecting Coastal Life: Early Warning Systems
The ocean can also present significant hazards, such as cyclones (large rotating storms) and tsunamis (giant waves caused by underwater earthquakes). To mitigate these risks, early warning systems are essential.
Modern systems utilize a sophisticated network:
- Detection: Seismic stations detect undersea earthquakes in real time.
- Tracking: Coastal tide gauges and radars monitor sea-level changes.
- Confirmation: Ocean Bottom Pressure Recorders (OBPRs) on the seafloor confirm the passage of tsunami waves.
- Dissemination: Alerts are sent via satellites to government agencies and directly to the public through SMS and other channels.
In India, technologies like the GEMINI device provide fishermen with real-time satellite information regarding waves, winds, and tsunami warnings in their local languages, significantly enhancing maritime safety.
