Question

Why is much of the open ocean, in effect, a 'marine desert'?

Short answer

The open ocean is a 'marine desert' due to limited nutrients, insufficient upwelling, and reduced sunlight in deep water areas, leading to low biological productivity.

Step-by-step solution

Understanding 'marine desert'

A 'marine desert' refers to areas in the ocean that have low biological productivity. These regions have sparse marine life due to limited nutrients required to support a thriving ecosystem.

Analyzing Nutrient Distribution

Deep ocean waters and certain surface areas lack mixing, which means nutrients found in deeper waters don't reach the surface. This stratification prevents nutrient-rich waters from saturating the photic zone where photosynthesis occurs.

Exploring Ocean Currents and Winds

Ocean currents and wind patterns affect the distribution of nutrients. Areas where currents do not bring up nutrient-rich deep waters (upwelling) typically remain low in productivity.

Examining Light Availability

Light availability is crucial for photosynthesis, yet in open ocean areas, the photic zone can be too deep or limited, reducing the potential for photosynthetic organisms like phytoplankton to thrive.

Evaluating Food Webs

The lack of phytoplankton limits the entire food webs in these regions. As primary producers are scarce, there is less food for other organisms, resulting in a 'desert-like' environment in terms of biodiversity.

Key concepts

Biological Productivity

Marine deserts are vast ocean areas with low biological productivity. This means these regions do not support much marine life due to limited resources. Biological productivity in oceans refers to the rate at which marine plants, like phytoplankton, produce organic matter through photosynthesis. Highly productive areas are teeming with sea life because they provide food at the base of the food web. However, in marine deserts, the scarcity of essential nutrients hinders the growth of these producers.
Biological productivity is essential for maintaining diverse marine ecosystems. Without it, there’s less food available to support fish, marine mammals, and other organisms. Because of this, marine deserts have significantly lower biodiversity compared to other oceanic zones.

Nutrient Distribution

Nutrient distribution in the ocean is critical for supporting marine life. Nutrients like nitrogen, phosphorous, and iron are necessary for phytoplankton growth, yet not all ocean regions receive an equal share. In marine deserts, nutrient distribution is uneven, and necessary nutrients are often locked in deeper waters.
Due to ocean stratification, nutrients remain trapped beneath the surface layers of water. The lack of vertical mixing prevents these nutrients from reaching the photic zone, the surface layer where sunlight enables photosynthesis. This overall lack of nutrients results in low biological productivity in marine deserts.

Ocean Currents

Ocean currents play a pivotal role in nutrient distribution across the ocean. They can determine which areas are rich or poor in nutrients. In some regions, currents bring nutrient-rich waters to the surface through a process known as upwelling. Upwelling regions are typically very productive, supporting vibrant ecosystems.
However, marine deserts are characterized by a lack of upwelling. Currents in these regions do not bring sufficient nutrients to the surface, thus limiting biological productivity. As such, the open ocean's wide expanses with minimal current activity often remain marine deserts.

Photosynthesis

Photosynthesis is the foundation of life in ocean ecosystems. This process involves converting sunlight into chemical energy, creating organic matter that sustains marine life. For effective photosynthesis, sunlight must penetrate the surface waters where phytoplankton reside.
In marine deserts, the photic zone—the area where sunlight can support photosynthesis—may be deeper or limited in extension. This makes it challenging for phytoplankton to perform photosynthesis efficiently. Without enough phytoplankton, the entire food web suffers, leading to low biological productivity.

Food Webs

Food webs in the ocean start with primary producers like phytoplankton, which convert sunlight into energy through photosynthesis. These producers are crucial for sustaining marine life, serving as the base of the food web. In marine deserts, the limited population of phytoplankton means there’s less energy available to fuel other organisms.
As a result, the food webs in these regions are unbalanced. With fewer primary producers, there is also less food for herbivores and, consequently, fewer predators. This leads to a 'desert-like' environment with sparse marine life, highlighting the importance of nutrient-rich waters and productive food webs for a thriving ocean ecosystem.