Question

A large proportion of the open ocean is, in effect, a marine desert. Why?

Short answer

Marine deserts lack sufficient nutrients for diverse biological activity.

Step-by-step solution

Introduction to Ocean Deserts

Many parts of the open ocean are considered 'marine deserts' because they lack the nutrients necessary to support a diverse range of life.

Understanding Nutrient Distribution

Key nutrients such as nitrogen and phosphorus are often found near coastlines where rivers and runoff introduce them into the ocean. In the open ocean, these nutrients are not as readily available.

Role of Ocean Currents

Ocean currents play a significant role in distributing nutrients. In many open ocean areas, there are fewer currents to bring nutrients from deeper waters to the surface.

Photosynthesis and Plankton

Phytoplankton, which rely on sunlight and nutrients for photosynthesis, are scarce in nutrient-poor marine deserts. This scarcity affects the entire food chain.

Key concepts

Nutrient Distribution

The distribution of nutrients in the ocean is a crucial factor influencing marine life.
Nutrients like nitrogen and phosphorus are essential for the growth of phytoplankton, which form the base of the ocean food web.
Near coastlines, these nutrients are more abundant because rivers, runoff, and even upwelling events deliver them into the waters.
However, in the vast open ocean, these nutrients are less accessible.

• Coastal areas receive a continuous supply of nutrients from rivers and terrestrial sources.
• Rivers carry organic materials and minerals into the oceans, enriching the waters with essential nutrients.
• Runoff from land contributes additional nutrients, especially in regions of heavy rainfall.

In contrast, the open ocean, often referred to as a marine desert, lacks these nutrient inputs.
Thus, the limited availability of nitrogen and phosphorus in these regions restricts the growth and reproduction of phytoplankton, leading to less biodiversity.

Ocean Currents

Ocean currents are like the highways of the sea, moving water and nutrients around the globe.
They play a vital role in the distribution of nutrients within the ocean, impacting where marine life can thrive.
In coastal zones, currents often bring nutrient-rich water from the ocean depths to the surface, a process known as upwelling.
However, in open ocean areas, such currents are less frequent, contributing to their 'desert' status.

• Currents can carry cold, nutrient-rich water from the deep ocean upward, benefiting coastal ecosystems.
• Ocean gyres, large systems of circular ocean currents, can isolate water in the central parts of oceans, creating nutrient-poor regions.
• The movement of these currents is influenced by wind patterns, the Earth's rotation, and water temperature differences.

Without strong currents to transport nutrients from the depths, the open ocean remains nutrient-poor.
This limits the growth of phytoplankton and affects the wider marine food web.

Phytoplankton

Phytoplankton are microscopic marine organisms that are vital to the ocean ecosystem.
Often referred to as the "grass of the sea," these small plants use photosynthesis to grow, requiring sunlight and nutrients like nitrogen and phosphorus.
In nutrient-rich areas, phytoplankton thrive, serving as the primary food source for a wide range of oceanic life forms, from tiny zooplankton to large whales.

• Phytoplankton perform photosynthesis, producing oxygen and forming the base of the marine food web.
• Lacking in nutrients, phytoplankton populations decline, which impacts the entire food chain.
• They also play a role in carbon dioxide absorption, helping to regulate the Earth's climate.

In open ocean "deserts," where nutrients are scarce, phytoplankton cannot grow abundantly.
This shortage creates a cascading effect, limiting the availability of food for higher trophic levels, such as fish and marine mammals.
Thus, the ecological productivity of these ocean areas remains low.