An Overview of Ocean Bottom Topography

OCEAN BOTTOM TOPOGRAPHY

Through the GLOMAR expedition, ocean bottom studies and relief features were objectively known. The several relief features are: 1. Sea Mountains

• Knolls: These are small, pointy submarine mountains.
• Island: These are sea mountains which extend above the sea surface.
• Guyot: These are flat-topped mountains.

2. Trench Trenches are formed at zones of convergence where the oceanic crust goes under subduction. 3. Mid-Oceanic Ridge Mid-oceanic ridges are formed at zones of divergence. The zone where trenches are formed is known as active margins. The abyssal plains near active margins are rough and coarse, whereas passive margin abyssal plains are smooth. Similarly, the continental rise is formed at passive margins due to active deposition.

Ocean Currents

The ocean surface is not stationary. There are several movements on the ocean surface, kind of like rivers in the ocean. Currents originate due to various forces and are of two types – warm and cold.

Factors Generating Ocean Currents

1. Rotation of the Earth: Earth rotates from west to east. Based on Newton’s 1st and 2nd laws of motion, ocean currents start to flow from east to west.
2. Coriolis Force: The Earth’s rotation deflects water due to the Coriolis force. It deflects to the right in the northern hemisphere and to the left in the southern hemisphere. This forms circular movements called gyres. The center of the gyre is nearly stationary, promoting the growth of algae such as sargassum, forming regions like the Sargasso Sea.
3. Planetary Winds: Permanent winds are a major factor driving ocean currents. For example, equatorial currents are influenced by trade winds, and the North Atlantic Drift is influenced by westerlies.
4. Coastline Configuration: The shape of coastlines directly impacts current direction and movement, e.g., the Antilles Current.
5. Influence of Solar Insolation: Maximum solar energy is received near the tropics, causing thermal expansion of water. This raises equatorial water by 8–10 cm compared to mid-latitudes, creating a gentle slope that drives ocean currents from the equator.

Major Ocean Currents

• North Equatorial Current: Significant in the Pacific and Atlantic, flowing 5°–15° north from east to west due to Earth’s rotation, trade winds, and thermal expansion.
• South Equatorial Current: Significant in the Atlantic, Indian, and Pacific Oceans, flowing 5°–15° south.
• West Wind Drift (Antarctic Circumpolar Current): Flows west to east under the influence of westerlies and absence of landmass.

Ocean currents move in circular patterns called gyres. One of the most notable gyres is in the North Atlantic Ocean. Each gyre has four ocean currents:

• Equatorial Current
• Western Boundary Current
• Polar Current
• Eastern Boundary Current

Fishing Grounds and Population Distribution

The regions where cold and warm currents meet are excellent fishing grounds. Examples include:

• Newfoundland, Canada (Labrador + Gulf Stream)
• South Africa
• Hokkaido, Japan (Oyashio + Kuroshio)

Population distribution is also influenced by ocean currents. For example, Hokkaido has a low population due to the cold Oyashio Current, whereas Anchorage, Alaska, has a higher population because of the warm Alaskan Current (extension of the Kuroshio Current).

Blog by –
Ms. Sarika Gupta
Assistant Professor of Political Science
Biyani Girls College