The Earth is an oblate, heterogeneous spheroid that revolves on its axis and is susceptible to gravitational influences from other planets and the sun. These elements, as well as geographic changes in continents and submerged terrains, climatic systems, water volume, tectonics, and others, influence the ocean’s surface and therefore sea level.
As a result, sea level can be defined in different ways, depending on the context and the reference frame used for measurement. Some of the key definitions of sea level are as follows:
Local Sea Level: The height of seawater with a fixed place on land used as a continuous reference Meteorological conditions, tidal range, ocean currents, and subsidence and uplift rates all have an impact. Also known as “Relative Sea level.”
Mean Sea Level (MSL): The average height of seawater in relation to a given datum, determined by a statistical average of water heights across time. This is the most practical definition of sea level because it aids in determining the height of all sites on Earth (topographic and bathymetric elevation).
Global Mean Sea Level (GMSL): The average height of the Earth’s oceans combined (relative to the Earth’s centre). It is mostly influenced by elements such as seawater volume, ocean basin size, and so on. Also known as “Eustatic Sea Level.”
How Do We Determine the Depth of The Sea Level?
Sea level elevation is defined as 0 feet, which serves as the universal reference point for measuring elevations on Earth’s surface. Locations above sea level are assigned positive elevations, while locations below sea level are attributed negative elevations.
Determining sea level involves a multi-faceted approach using a combination of techniques and measurements from various sources. Satellite altimetry, which measures the time taken for microwave signals to bounce back from the ocean surface, provides a global perspective on sea level changes.
Tide gauges installed at coastal locations record local tidal fluctuations. GPS surveying calculates the elevation of fixed points on land, allowing scientists to derive local sea levels.
Satellite gravity measurements indirectly offer insights into ocean mass and density variations. Oceanographic measurements provide direct data on sea level, currents, and water properties.
Computational models combine and interpret these datasets, aiding in understanding complex interactions and long-term sea level trends. This comprehensive methodology enables accurate monitoring and analysis of sea level changes, yielding vital information about climate patterns and potential impacts on coastal regions.
Sea Vs Ocean: What’s The Depth Difference?
The terms “sea” and “ocean” are often used interchangeably, but they can have different connotations depending on the context. In a general sense, seas are smaller bodies of saltwater that are partially enclosed by land, while oceans are much larger and cover vast expanses of the Earth’s surface.
Depth Difference
When it comes to depth, there is no strict rule differentiating seas from oceans. Some seas can be deeper than certain oceans, and vice versa. Here are approximate average depths for some notable seas:
Mediterranean Sea:
- Average depth: About 1,500 meters (4,921 feet)
- Maximum depth: Calypso Deep – Approximately 5,267 meters (17,280 feet)
Caribbean Sea:
- Average depth: About 2,575 meters (8,448 feet)
- Maximum depth: Cayman Trough – Approximately 7,686 meters (25,220 feet)
Arabian Sea:
- Average depth: About 2,850 meters (9,350 feet)
- Maximum depth: Unknown (estimated around 6,000 meters or 19,685 feet)
North Sea:
- Average depth: About 95 meters (312 feet)
- Maximum depth: Norwegian Trench – Approximately 700 meters (2,297 feet)
South China Sea:
- Average depth: About 1,460 meters (4,790 feet)
- Maximum depth: Unknown (estimated around 5,000 meters or 16,404 feet)
Black Sea:
- Average depth: About 1,253 meters (4,111 feet)
- Maximum depth: Crimean Abyssal – Approximately 2,212 meters (7,257 feet)
Red Sea:
- Average depth: About 490 meters (1,610 feet)
- Maximum depth: Central Trough – Approximately 3,040 meters (9,970 feet)
Baltic Sea:
- Average depth: About 55 meters (180 feet)
- Maximum depth: Landsort Deep – Approximately 459 meters (1,506 feet)
Meanwhile, some oceans have areas with relatively shallow depths. For example, the North Sea and the Persian Gulf, both considered seas by some definitions, are shallower in comparison to other parts of the global oceans. Here are approximate values for some of the major oceans:
Pacific Ocean:
- Average depth: About 3,970 meters (13,025 feet)
- Deepest point: Mariana Trench (Challenger Deep) – Approximately 10,928 meters (35,856 feet)
Atlantic Ocean:
- Average depth: About 3,646 meters (11,962 feet)
- Deepest point: Puerto Rico Trench – Approximately 8,376 meters (27,480 feet)
Indian Ocean:
- Average depth: About 3,741 meters (12,274 feet)
- Deepest point: Java Trench (Sunda Trench) – Approximately 7,725 meters (25,344 feet)
Southern Ocean (Antarctic Ocean):
- Average depth: About 4,000 meters (13,123 feet)
- Deepest point: South Sandwich Trench – Approximately 7,235 meters (23,737 feet)
Arctic Ocean:
- Average depth: About 1,205 meters (3,953 feet)
- Deepest point: Eurasian Basin (Molloy Deep) – Approximately 5,550 meters (18,208 feet)
What Is The Deepest Sea Level Ever Reached By Humans
The deepest sea level ever reached by humans was in the Challenger Deep, which is located in the Mariana Trench in the western Pacific Ocean. The depth reached was approximately 10,928 meters (35,856 feet) below sea level.
This historic dive took place on January 23, 1960, when Jacques Piccard, a Swiss oceanographer, and Don Walsh, a U.S. Navy lieutenant, descended into the Challenger Deep aboard the bathyscaphe Trieste. They spent about 20 minutes on the ocean floor before returning to the surface.
The Mariana Trench expedition last year achieved two historic milestones. Firstly, it marked the deepest crewed dive in history, descending an incredible 10,927 meters into the Challenger Deep. Secondly, the expedition was significant for another reason: astronaut Kathy Sullivan became the first woman ever to venture into the depths of the Challenger Deep. Her presence on the dive added an extraordinary and groundbreaking dimension to the mission.