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Oceanic deserts

Oceanic deserts is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Oceanic deserts rather than just read about it. In short: Oceanic deserts are regions of the oceans characterized by low annual precipitation, comparable to that of continental deserts. These areas typically overlap with subtropical gyres - large systems of circular ocean currents formed by the global wind patterns.

Oceanic deserts — main illustration
Oceanic deserts — illustration

Key takeaways

  • Oceanic deserts belongs to earth science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Oceanic deserts to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Oceanic deserts from memory before moving on to harder problems.

Reference excerpt

Oceanic deserts are regions of the oceans characterized by low annual precipitation, comparable to that of continental deserts. These areas typically overlap with subtropical gyres - large systems of circular ocean currents formed by the global wind patterns. These gyres are characterized by semi-permanent high-pressure systems, which inhibit the formation of deep precipitating clouds. Unlike continental deserts, oceanic deserts maintain a relatively high cloud fraction throughout the year. Despite the pronounced cloud cover, the low level shallow clouds over these areas produce very little precipitation, distinguishing these areas as oceanic deserts. The term "desert" in this context not only refers to the low precipitation but also to the low biodiversity found in these regions. The oceanic circulation in these regions significantly impacts marine life, leading to lower productivity and biodiversity compared to other parts of the ocean.

Geographic distribution Oceanic deserts are primarily found in the eastern subtropical oceans. The corresponding subtropical gyres are the North Atlantic Gyre extends from the eastern coast of North America to the western coast of Europe and Africa. The South Atlantic Gyre is located off the coast of South America, stretching towards Africa. The North Pacific Gyre spans from the western coast of North America to the eastern coast of Asia. The South Pacific Gyre is found off the coast of South America, extending to the western Pacific. The Indian Ocean Gyre is positioned between the eastern coast of Southern Africa and the western coast of Australia.

Climatic and atmospheric conditions

Oceanic deserts are influenced by several key atmospheric and climatic factors. Persistent high-pressure systems, known as subtropical highs, dominate these regions, leading to stable atmospheric conditions. The stable high-pressure zones prevent the development of deep convective clouds, which are necessary for rainfall. As a result, annual precipitation in oceanic deserts is minimal, comparable to the aridity observed in terrestrial deserts. Despite the low precipitation, oceanic deserts maintain a relatively high cloud fraction throughout the year (see figure 2). Coastal regions typically see stratus clouds, while offshore areas are characterized by stratocumulus clouds. Over the relatively warm ocean to the west, trade-wind cumuli are common. The cloud cover in these regions is largely non-precipitating, contributing to the persistent dry conditions. This is in contrast to continental deserts, which generally have clear skies with occasional, but often intense, rainfall events. A key feature of the atmospheric profile in oceanic deserts is the presence of the trade wind inversion. The vertical profiles of meteorological parameters such as temperature, humidity, and wind speed in oceanic deserts reveal sharp gradients at the inversion layer. This inversion layer, found at an altitude of about 1 to 2 kilometers, acts as a cap that limits vertical mixing and the development of deep convective clouds and thus contributes to the suppression of precipitation.

Oceanographic features

Oceanic deserts are depicted in dark blue on maps produced by NASA (see figures 1 and 3), indicating areas with low precipitation and low chlorophyll concentrations, highlighting their status as nutrient-starved oceanic regions. However, the coastal zones in these oceanic deserts have a relatively high productivity and biodiversity due to deposition of nutrient rich continental sediment by surface runoff as well as upwelling of cold ocean waters induced by prevailing winds and rising sea floors brings iron and other essential nutrients to the surface. This includes the equator zone. The physical characteristics of oceanic deserts significantly influence their ecological dynamics. Strong stratification in these regions prevents the mixing of nutrient-rich deep waters with surface waters, maintaining nutrient-poor conditions at the surface. This stable stratification is a result of the warm, saline surface waters overlaying cooler and denser deep waters, which inhibits vertical mixing. Nutrient depletion in subtropical gyres is primarily due to strong downwelling and particle sinking. In contrast, regions with the highest chlorophyll concentrations are found in cold waters, where nutrient-rich upwelling occurs, allowing phytoplankton to thrive.

References

Illustrations

Oceanic deserts: Ocean gyres and currents from Atlas of World Maps. (Army Service Forces Manual M-101, 1943)
Ocean gyres and currents from Atlas of World Maps. (Army Service Forces Manual M-101, 1943)
Oceanic deserts: Figure 1: Global average annual precipitation. Dark blue areas indicating regions with low precipitation amount. The eastern basin of subtropical oceans are distinguished with low precipitation. (NASA SVS, 2023)
Figure 1: Global average annual precipitation. Dark blue areas indicating regions with low precipitation amount. The eastern basin of subtropical oceans are distinguished with low precipitation. (NASA SVS, 2023)
Oceanic deserts: Figure 2: Average of all of the satellite’s cloud observations between July 2002 and April 2015. Colors range from dark blue (no clouds) to light blue (some clouds) to white (frequent clouds). (Earth Observatory NASA, 2015)
Figure 2: Average of all of the satellite’s cloud observations between July 2002 and April 2015. Colors range from dark blue (no clouds) to light blue (some clouds) to white (frequent clouds). (Earth Observatory NASA, 2015)
Oceanic deserts: Figure 3: This composite image gives an indication of the magnitude and distribution of global primary production, both oceanic (mg/m3 chlorophyll a) and terrestrial (normalized difference land vegetation index). (Visible Earth NASA, 2009)
Figure 3: This composite image gives an indication of the magnitude and distribution of global primary production, both oceanic (mg/m3 chlorophyll a) and terrestrial (normalized difference land vegetation index). (Visible Earth NASA, 2009)

Worked examples

Example 1 — a first encounter with Oceanic deserts

Start with the simplest possible case. Write down what Oceanic deserts claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Oceanic deserts before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Oceanic deserts ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Oceanic deserts

In research
Oceanic deserts appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Oceanic deserts in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Oceanic deserts is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ecosystems, Oceans, so understanding it makes those chapters shorter.
In everyday life
Look for Oceanic deserts outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Oceanic deserts in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Oceanic deserts means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Oceanic deserts out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Oceanic deserts in simple terms?

Oceanic deserts are regions of the oceans characterized by low annual precipitation, comparable to that of continental deserts. These areas typically overlap with subtropical gyres - large systems of circular ocean currents formed by the global wind patterns.

Why does Oceanic deserts matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Oceanic deserts?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Oceanic deserts.

Tags

  • Ecosystems
  • Oceans

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