Bathymetric method

Introduction

The bathymetric method involves measuring the depths of oceans, seas, and other water bodies to map the underwater topography. These measurements help us understand the physical features of the ocean floor, such as ridges, trenches, continental shelves, and slopes. This field is crucial for various applications, including navigation, oceanography, resource exploration, and environmental monitoring.

Bathymetric Technique & Hypsographic Curve

Challenger Expeditions

What was it?

The H.M.S. Challenger Expedition (1872-1876), led by Wyville Thomson, was the first comprehensive scientific exploration of the world’s oceans. It played a pivotal role in advancing our knowledge of oceanography.

How was it conducted?

The expedition had a broad mandate to study the ocean’s properties, such as:

• Salinity
• Temperature
• Density
• Precipitates on the ocean floor

It also mapped the ocean floor using a line-sounding technique, a method that was first used by scientist John Murray during this expedition.

The Glomar Challenger Expedition (US, 1968)

Objective

The Glomar Challenger Expedition focused on:

• Studying the ocean crust rocks
• Mapping the ocean floor
• Analyzing ocean water properties

Subproject: Deep Sea Drilling Project (DSDP)

The DSDP was a significant subproject that provided insights into:

• Determining the age of the ocean floor
• Understanding the composition of oceanic rocks and basalt
• Mapping the Atlantic Mid-Ocean Ridge (MOR) and discovering deep trenches

These findings laid the foundation for the Sea Floor Spreading Hypothesis proposed by Harry Hess, which explained how tectonic plates move.

Joint Oceanographic Institutions for Deep Earth Sampling (JOIDES)

What is JOIDES?

JOIDES represents a collaborative effort of universities dedicated to exploring the geology beneath the ocean floor.

How does it work?

The organization continues the drilling projects started in earlier expeditions, aiming to discover new resources and further understand the deep-sea environment.

Hypsographic Curve

What is it?

The Hypsographic Curve (or Bathymetric Curve) depicts the proportion of land above and below sea level at different elevations and depths. It visually represents the Earth’s surface features, showing how much of the Earth’s surface is at specific elevations or depths.

How is it structured?

• Continents: Cover around 30% of the Earth’s surface.
• Ocean Floor: Accounts for approximately 70%.
• Shelf and Slope: Make up about 8-10% of the total surface area.
• Deep Ocean Floor: Constitutes about 50% of the Earth’s total surface.
• Trenches and Mid-Ocean Ridges (MOR): Less than 1% of the Earth’s surface.
• The average height above sea level is about 840 meters.
• The average depth below sea level is around 3,800 meters.

This curve helps in visualizing Earth’s elevation patterns, from the highest mountain peaks to the deepest ocean trenches.

Bathymetric Techniques

1. Line Sounding Technique

Who developed it?

This technique was popularized by John Murray during the Challenger Expedition.

What is it?

Line sounding is one of the earliest methods used to measure ocean depth, involving a weighted line that is lowered into the water until it touches the ocean floor.

How does it work?

• A weighted rope (sounding line) is dropped from a ship.
• When the weight hits the sea floor, the line goes slack.
• The length of the line is then measured to determine the ocean’s depth at that point.

Limitations:

• It was a crude and time-consuming method.
• It often resulted in errors due to factors such as waves, currents, and the stretching of the rope.

2. Echosounder (SONAR)

What is it?

The Echosounder technique, also known as SONAR (Sound Navigation and Ranging), revolutionized bathymetric mapping by using sound waves to measure ocean depths.

How does it work?

• A pulse of sound waves is released from the ship toward the ocean floor.
• These sound waves travel through the water, hit the ocean floor, and bounce back to the surface.
• The time it takes for the echo to return is measured and used to calculate the depth.

This technique is more accurate than line sounding and is widely used in modern oceanographic studies. However, radio waves cannot be used in this technique since water efficiently absorbs them, hence the reliance on sound waves.

3. Satellite Technique

What is it?

The Satellite Technique is a modern, remote sensing method used to measure bathymetry more accurately from space.

How does it work?

• Satellites equipped with advanced sensors scan the ocean’s surface.
• They detect even slight fluctuations in sea level, which reflect the topography of the ocean floor beneath.

Advantages:

• More accurate and comprehensive than other methods.
• Can cover vast areas of the ocean quickly and efficiently.

Conclusion

The development of bathymetric techniques, from the traditional line sounding to the advanced satellite techniques, has significantly enhanced our understanding of the ocean floor. These methods provide valuable data that help in various fields such as oceanography, geology, navigation, and resource exploration.

1. How did advancements in bathymetric techniques, such as the shift from line sounding to satellite technology, revolutionize our understanding of the ocean floor’s topography? (250 words)
2. Discuss the significance of the hypsographic curve in understanding Earth’s elevation and depth distribution. How does it contribute to geological and oceanographic studies? (250 words)
3. Explain the importance of bathymetric studies conducted by the Challenger and Glomar Expeditions in shaping modern oceanographic theories, particularly the concept of sea floor spreading. (250 words)