Major Physical and Biological Differences Between Seas and Oceans
Sea and ocean are both water bodies yet they share many differences and similarities among them. We may think that both just contain water in them and what might be the possible difference, but still, there are major differences, facts, and points about both that separate them from each other.
What is an Ocean?
Oceans are water bodies that incorporate more than 70% of the earth’s surface. There are five oceans in the world. Namely the Pacific Ocean, Indian Ocean, Arctic Ocean, Atlantic Ocean, and the Southern Ocean. Oceanography or oceanology is the study of physical and biological characteristics and features of the ocean and its organisms. The ocean water is alkaline and makes them unfit for drinking. The rivers have carried the minerals, rocks, and soil from the land and brought them to the ocean, which makes the ocean salty. The minerals are mostly sodium and chloride which make up the common salt.
It can be seen that oceans are not bordered or separated by any landmarks. Hence, all the oceans combine to make a single large water body on the earth’s surface. To our convenience, we have grouped the ocean based on its location. The Arctic ocean is named after the arctic region likewise the Indian ocean is named after India which is approximate to the ocean.
It is observed that the oceans that approximate the north and the south poles are less saline in nature than the oceans which are situated more towards the equator. This is because the tropical region receives more sunlight than the poles. So the water in those regions evaporates faster and concentrates on the water.
The color of the ocean is mostly blue as perceived. It would be fascinating as we have learned that water does not have any color yet we perceive oceans and seas in blue color. This is because the sunlight that is emitted on the water bodies has different wavelengths of light. The red part of the sunlight is absorbed resulting in the blue color of the light being reflected back to the atmosphere.
Tides
Tides are the rising and falling of water in the ocean and other water bodies. It is mainly seen in large water bodies like oceans and seas. The tides are caused due to the exertion of the moon’s gravity on earth. Since the moon revolves around the earth, it exerts a gravitational pull towards the earth’s surface. Since the earth rotates around its axis, the side facing the moon experiences a high tide which is a bulge in the ocean. Which keeps changing as the earth keeps rotating. On the day of a full moon and new moon, the earth and sun and moon align with one another causing a maximum bulge in the ocean. These are called High Tides. And the area opposite to the earth’s surface will experience low tides. Hence, oceans keep experiencing high tides and low tides frequently throughout the time of rotation and revolution.
Waves
Waves are the motion of water in oceans caused by the wind. The wind shifts some of the energy to the water molecules when it moves over the surface of the ocean. This causes water to move in oceans and seas. It may seem that waves are moving in a horizontal direction, but they just move vertically.
What is a Sea?
Seas are the water bodies that are smaller than the ocean, and partially landlocked on either of the sides. There are few seas that are fully landlocked saltwater lakes like the Caspian Sea or the Dead Sea which is technically a lake but still called Sea. There are also seas that contain freshwater, one example is the Sea of Galilee.
The seas also have similar features as that of the oceans. It also consists of waves, tides, and water currents. Sea currents are the flow of the water within the sea which travel in different directions based on geography, temperature, wind, and ocean currents. The salinity of the sea is measured with the unit of parts per thousand (%), the normal seawater is very alkaline. It normally ranges about 35%, but the seas like the Mediterranean Sea are about 38%. In landlocked saltwater lakes, the density of the salt in water is too high ranging about 300% given an example of the dead sea.
A water cycle is the main event that takes place in almost all the water bodies. The water from the seas, oceans, lakes and other water bodies evaporates into the sky forming clouds. The clouds become denser and start cooling down eventually, causing the water to come back to the earth in the form of rain. This event is very important as rainwater plays a major role in plant growth, agriculture, and many other events.
Coasts
Coasts are an important feature of seas. It is the point where the land meets the water body. The coastline is the total length of the area that surrounds the land, particularly when we look into the geography of a land. Beaches are areas covered with sand and rocks near the sea where people may come to relax for a vacation.
Creatures of the Sea
Marine life are extremely important for the survival of the biosphere, as the carbon cycle is regulated by the creatures of the sea and ocean. The range of creatures living in the sea is abundant. It can start from small phytoplankton to large whales. Here marine life is divided into coastal habitats and open water habitats. The coastal habitats range from the coastline of seawater and may go up to the continental shelf whereas the open water inhabitants live in the center of the sea or ocean.
Phytoplanktons produce almost half of the world’s oxygen and are the primary producers of the marine ecosystem.
Difference Between Ocean and Sea
Human uses of the Ocean Bodies
Ocean waters are one of the greatest resources known to mankind. It offers a very large supply of energy by means of the ocean waves, tides, salinity differences, and ocean temperature differences which have been in the recent decades actively harnessed to meet the growing energy needs. Offshore wind power is captured by wind turbines placed out on the ocean to generate electricity. It has the added advantage because wind speeds are higher in the oceans than on land, even though the cost of such offshore constructions can be very high in these wind farms. The ocean floors also have a huge deposit of conventional fuels like petroleum, crude oil, and natural gas, in rocky ocean floors.
Throughout history, these water bodies have served a wide variety of purposes, including navigation and exploration, naval warfare, travel, shipping and trade, food production (fishing, seaweed farming, and aquaculture), leisure (sailing, scuba diving, etc.), power generation and many more.
Threats to Marine Biodiversity
The greatest threat to marine life forms is from humans and unchecked human exploitation of marine resources. The constant buildup of unwanted foreign matter such as marine debris and microplastics, along with overfishing, ocean acidification, etc., have had adverse effects of climate change on oceans.
Marine Pollution
Marine pollution refers to the type of pollution in which substances used or discarded by humans, such as industrial, agricultural, and residential waste, particles, noise, excess carbon dioxide or invasive organisms enter the ocean waters by intentional dumping or accidental release and cause harmful effects there.
FAQs on Sea vs Ocean: What’s the Difference in Biology?
1. What is the main difference between a sea and an ocean?
The primary difference is size and enclosure. An ocean is a vast, continuous body of saltwater that covers about 70% of the Earth. A sea is a smaller body of saltwater that is often partially enclosed by land. For example, the Mediterranean Sea is enclosed by Europe, Africa, and Asia, while the Atlantic is a massive ocean connecting continents.
2. Which is generally deeper, a sea or an ocean?
Oceans are significantly deeper than seas. Seas are shallower because they are often located over continental shelves. The deepest part of any ocean, the Mariana Trench in the Pacific Ocean, is far deeper than any point in a typical sea.
3. Can a sea be part of an ocean? Please provide an example.
Yes, most seas are considered part of a larger ocean. These are called marginal seas. They are connected to the open ocean but are distinct due to their partial enclosure by land. A good example is the Arabian Sea, which is the northwestern part of the Indian Ocean.
4. What are some key points of comparison between seas and oceans?
The key differences can be understood through these points:
- Size: Oceans are vast and interconnected global water bodies; seas are smaller.
- Depth: Oceans have a much greater average depth compared to the shallower seas.
- Marine Life: While both host diverse life, the types of species can differ. Seas often have unique ecosystems due to their proximity to land, while oceans contain deep-sea creatures adapted to extreme pressure and darkness.
- Boundaries: Oceans are bounded by continents, while seas are often bounded by smaller landmasses or islands.
5. Why is the phrase 'the Seven Seas' used when there are only five oceans?
The term 'the Seven Seas' is an ancient and figurative expression used by sailors and in literature to refer to all the world's oceans. It doesn't represent a scientific count. Geographically, the Earth has five major oceans: the Pacific, Atlantic, Indian, Southern (Antarctic), and Arctic oceans.
6. How do oceans and seas support life on Earth?
They play a vital role by hosting a vast range of biodiversity, from microscopic phytoplankton to the largest animal, the blue whale. Phytoplankton are crucial as they produce a large portion of the Earth's oxygen through photosynthesis. These water bodies are also a primary source of food and resources for humans.
7. How do these large bodies of water influence the world's climate?
Oceans act as massive heat reservoirs, absorbing solar energy and distributing it around the globe through currents. This process helps regulate global temperatures and weather patterns. They are also a critical part of the water cycle and act as a major carbon sink, absorbing significant amounts of carbon dioxide from the atmosphere.
8. Why might the water from two different oceans appear not to mix?
This visual effect, often seen where oceans meet, is due to differences in water density, temperature, and salinity (salt content). This creates a boundary called a halocline. Although the waters appear separate, they do slowly mix over time, but the distinct properties make the separation visible at the surface.
