People often use the terms “sea” and “ocean” interchangeably, but to geographers, they are distinct. A sea is defined as a division of the ocean that is enclosed or partly enclosed by land. Because of this connection to the ocean, all seas are saline, or salty. You might be surprised to learn that there are over 50 seas on Earth, each with unique characteristics. Some are even called bays, like the Bay of Bengal, while others, like the Caspian Sea, are actually lakes. So, How Many Seas Are There and what are the different types? Let’s dive into the fascinating world of seas to understand their classifications and examples.
There are three primary classifications of seas based on their geographical characteristics: nearly enclosed seas, partly enclosed seas, and hypersaline lakes. Each type presents distinct features in terms of their connection to the open ocean, water properties, and marine life.
Nearly Enclosed Seas: Almost Landlocked
Nearly enclosed seas are characterized by their deep penetration into continents and limited connection to the vast ocean through narrow waterways known as straits. The Mediterranean Sea and the Baltic Sea are prime examples of this category. Due to their almost landlocked nature, these seas typically exhibit a minimal range of tides, and some may even lack tides entirely. The restricted water exchange between nearly enclosed seas and the open ocean leads to significant differences in their physical, chemical, and biological attributes.
An aerial view showcasing the vast expanse of the Mediterranean Sea, a classic example of a nearly enclosed sea.
Consider the Red Sea as a compelling illustration. It is considerably saltier than the Indian Ocean, to which it connects via the narrow Bab-el-Mandeb strait. The marine organisms, including vibrant coral reefs, inhabiting the Red Sea have evolved to thrive in highly saline conditions. Remarkably, approximately 10 percent of the fish species found in the Red Sea are unique to this habitat and are not found in any other marine environment, including the adjacent Indian Ocean. This endemism highlights the isolated evolution within nearly enclosed seas.
Partly Enclosed Seas: Open Ocean Connections
Partly enclosed seas present a stronger resemblance to the open ocean, particularly in terms of water circulation patterns. The Weddell Sea in Antarctica serves as an example of a partly enclosed sea with a wide opening to the ocean. Consequently, the tides and marine life in the Weddell Sea closely mirror those of the Atlantic Ocean. The extensive connection allows for a greater exchange of water and marine species.
Icebergs float in the Weddell Sea, illustrating the open connection of partly enclosed seas to the broader ocean.
In contrast, other partly enclosed seas, such as the South China Sea, connect to the ocean through passages amidst islands. These islands, scattered across the South China Sea, are under the jurisdiction of countries like China, Malaysia, the Philippines, and Vietnam. The marine organisms inhabiting the South China Sea share similarities with those found throughout the South Pacific Ocean, indicating a biological link. While the tidal range is slightly reduced compared to the open ocean, the influence of oceanic tides is still evident in partly enclosed seas.
Hypersaline Lakes: Landlocked Seas with High Salt Content
Intriguingly, some saltwater bodies referred to as seas are actually lakes. These bodies of water were once part of ancient oceans or seas. Tectonic shifts, massive movements in the Earth’s crust, severed their connection to larger water bodies, resulting in their complete enclosure by land. These landlocked seas are often termed hypersaline lakes due to the exceptionally high concentration of salt in their waters.
The vast Caspian Sea, a hypersaline lake, bordered by multiple countries and showing its landlocked nature.
Among these landlocked seas is the Caspian Sea, situated between Europe and Asia. The Volga River flows into the northern part of the Caspian Sea. This freshwater input makes the northern region, within Russia and Kazakhstan, nearly a freshwater lake. However, the southern portion, located in Iran and Turkmenistan, exhibits significantly higher salinity levels. This salinity variation within a single hypersaline lake is a unique characteristic.
Another prominent example is the Dead Sea. The Jordan River flows into the Dead Sea, but notably, no rivers flow out. Water management practices for agriculture and industry have diverted Jordan River water. Due to canals and dams for irrigation and power generation, diminished water volumes reach the Dead Sea. Consequently, the Dead Sea is shrinking at an alarming rate of approximately one meter (3.3 feet) annually. Despite this rapid shrinkage, the Dead Sea is unlikely to completely disappear due to complex evaporation dynamics.
Tourists float effortlessly in the Dead Sea, famous for its high salinity and therapeutic properties.
The Dead Sea’s unique properties make it a popular tourist destination, renowned for its spas and historical sites. To address the shrinking water levels and boost regional economies, the governments of Israel, Jordan, and the Palestinian Authority are contemplating the Two Seas Canal project. This ambitious project proposes diverting water from the Red Sea to the Dead Sea, aiming to replenish water and create hydroelectric power dams across the Arabah desert.
However, the Two Seas Canal project has faced criticism due to potential environmental consequences. Concerns include the potential destruction of the delicate coral reef ecosystem in the Gulf of Aqaba by power plants, disruption of the Arabah aquifer impacting freshwater availability, and alteration of the Dead Sea’s unique saline ecosystem by introducing foreign species and different water quality. These environmental considerations are crucial in evaluating the feasibility of such large-scale water management projects.
In conclusion, while the exact number can fluctuate slightly depending on definitions and classifications, there are generally recognized to be more than 50 seas on our planet. These seas are categorized into nearly enclosed, partly enclosed, and hypersaline lakes, each exhibiting distinct characteristics and playing a vital role in Earth’s diverse aquatic ecosystems. Understanding the different types of seas helps us appreciate the complexity and interconnectedness of our oceans and their divisions.
